xact.c

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/*-------------------------------------------------------------------------
 *
 * xact.c
 *    top level transaction system support routines
 *
 * See src/backend/access/transam/README for more information.
 *
 * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/access/transam/xact.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include <time.h>
#include <unistd.h>

#include "access/multixact.h"
#include "access/subtrans.h"
#include "access/transam.h"
#include "access/twophase.h"
#include "access/xact.h"
#include "access/xlogutils.h"
#include "catalog/catalog.h"
#include "catalog/namespace.h"
#include "catalog/storage.h"
#include "commands/async.h"
#include "commands/tablecmds.h"
#include "commands/trigger.h"
#include "executor/spi.h"
#include "libpq/be-fsstubs.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "replication/walsender.h"
#include "replication/syncrep.h"
#include "storage/fd.h"
#include "storage/lmgr.h"
#include "storage/predicate.h"
#include "storage/proc.h"
#include "storage/procarray.h"
#include "storage/sinvaladt.h"
#include "storage/smgr.h"
#include "utils/catcache.h"
#include "utils/combocid.h"
#include "utils/guc.h"
#include "utils/inval.h"
#include "utils/memutils.h"
#include "utils/relmapper.h"
#include "utils/snapmgr.h"
#include "utils/timestamp.h"
#include "pg_trace.h"


/*
 *  User-tweakable parameters
 */
int         DefaultXactIsoLevel = XACT_READ_COMMITTED;
int         XactIsoLevel;

bool        DefaultXactReadOnly = false;
bool        XactReadOnly;

bool        DefaultXactDeferrable = false;
bool        XactDeferrable;

int         synchronous_commit = SYNCHRONOUS_COMMIT_ON;

/*
 * MyXactAccessedTempRel is set when a temporary relation is accessed.
 * We don't allow PREPARE TRANSACTION in that case.  (This is global
 * so that it can be set from heapam.c.)
 */
bool        MyXactAccessedTempRel = false;


/*
 *  transaction states - transaction state from server perspective
 */
typedef enum TransState
{
    TRANS_DEFAULT,              /* idle */
    TRANS_START,                /* transaction starting */
    TRANS_INPROGRESS,           /* inside a valid transaction */
    TRANS_COMMIT,               /* commit in progress */
    TRANS_ABORT,                /* abort in progress */
    TRANS_PREPARE               /* prepare in progress */
} TransState;

/*
 *  transaction block states - transaction state of client queries
 *
 * Note: the subtransaction states are used only for non-topmost
 * transactions; the others appear only in the topmost transaction.
 */
typedef enum TBlockState
{
    /* not-in-transaction-block states */
    TBLOCK_DEFAULT,             /* idle */
    TBLOCK_STARTED,             /* running single-query transaction */

    /* transaction block states */
    TBLOCK_BEGIN,               /* starting transaction block */
    TBLOCK_INPROGRESS,          /* live transaction */
    TBLOCK_END,                 /* COMMIT received */
    TBLOCK_ABORT,               /* failed xact, awaiting ROLLBACK */
    TBLOCK_ABORT_END,           /* failed xact, ROLLBACK received */
    TBLOCK_ABORT_PENDING,       /* live xact, ROLLBACK received */
    TBLOCK_PREPARE,             /* live xact, PREPARE received */

    /* subtransaction states */
    TBLOCK_SUBBEGIN,            /* starting a subtransaction */
    TBLOCK_SUBINPROGRESS,       /* live subtransaction */
    TBLOCK_SUBRELEASE,          /* RELEASE received */
    TBLOCK_SUBCOMMIT,           /* COMMIT received while TBLOCK_SUBINPROGRESS */
    TBLOCK_SUBABORT,            /* failed subxact, awaiting ROLLBACK */
    TBLOCK_SUBABORT_END,        /* failed subxact, ROLLBACK received */
    TBLOCK_SUBABORT_PENDING,    /* live subxact, ROLLBACK received */
    TBLOCK_SUBRESTART,          /* live subxact, ROLLBACK TO received */
    TBLOCK_SUBABORT_RESTART     /* failed subxact, ROLLBACK TO received */
} TBlockState;

/*
 *  transaction state structure
 */
typedef struct TransactionStateData
{
    TransactionId transactionId;    /* my XID, or Invalid if none */
    SubTransactionId subTransactionId;  /* my subxact ID */
    char       *name;           /* savepoint name, if any */
    int         savepointLevel; /* savepoint level */
    TransState  state;          /* low-level state */
    TBlockState blockState;     /* high-level state */
    int         nestingLevel;   /* transaction nesting depth */
    int         gucNestLevel;   /* GUC context nesting depth */
    MemoryContext curTransactionContext;        /* my xact-lifetime context */
    ResourceOwner curTransactionOwner;  /* my query resources */
    TransactionId *childXids;   /* subcommitted child XIDs, in XID order */
    int         nChildXids;     /* # of subcommitted child XIDs */
    int         maxChildXids;   /* allocated size of childXids[] */
    Oid         prevUser;       /* previous CurrentUserId setting */
    int         prevSecContext; /* previous SecurityRestrictionContext */
    bool        prevXactReadOnly;       /* entry-time xact r/o state */
    bool        startedInRecovery;      /* did we start in recovery? */
    struct TransactionStateData *parent;        /* back link to parent */
} TransactionStateData;

typedef TransactionStateData *TransactionState;

/*
 * CurrentTransactionState always points to the current transaction state
 * block.  It will point to TopTransactionStateData when not in a
 * transaction at all, or when in a top-level transaction.
 */
static TransactionStateData TopTransactionStateData = {
    0,                          /* transaction id */
    0,                          /* subtransaction id */
    NULL,                       /* savepoint name */
    0,                          /* savepoint level */
    TRANS_DEFAULT,              /* transaction state */
    TBLOCK_DEFAULT,             /* transaction block state from the client
                                 * perspective */
    0,                          /* transaction nesting depth */
    0,                          /* GUC context nesting depth */
    NULL,                       /* cur transaction context */
    NULL,                       /* cur transaction resource owner */
    NULL,                       /* subcommitted child Xids */
    0,                          /* # of subcommitted child Xids */
    0,                          /* allocated size of childXids[] */
    InvalidOid,                 /* previous CurrentUserId setting */
    0,                          /* previous SecurityRestrictionContext */
    false,                      /* entry-time xact r/o state */
    false,                      /* startedInRecovery */
    NULL                        /* link to parent state block */
};

/*
 * unreportedXids holds XIDs of all subtransactions that have not yet been
 * reported in a XLOG_XACT_ASSIGNMENT record.
 */
static int  nUnreportedXids;
static TransactionId unreportedXids[PGPROC_MAX_CACHED_SUBXIDS];

static TransactionState CurrentTransactionState = &TopTransactionStateData;

/*
 * The subtransaction ID and command ID assignment counters are global
 * to a whole transaction, so we do not keep them in the state stack.
 */
static SubTransactionId currentSubTransactionId;
static CommandId currentCommandId;
static bool currentCommandIdUsed;

/*
 * xactStartTimestamp is the value of transaction_timestamp().
 * stmtStartTimestamp is the value of statement_timestamp().
 * xactStopTimestamp is the time at which we log a commit or abort WAL record.
 * These do not change as we enter and exit subtransactions, so we don't
 * keep them inside the TransactionState stack.
 */
static TimestampTz xactStartTimestamp;
static TimestampTz stmtStartTimestamp;
static TimestampTz xactStopTimestamp;

/*
 * GID to be used for preparing the current transaction.  This is also
 * global to a whole transaction, so we don't keep it in the state stack.
 */
static char *prepareGID;

/*
 * Some commands want to force synchronous commit.
 */
static bool forceSyncCommit = false;

/*
 * Private context for transaction-abort work --- we reserve space for this
 * at startup to ensure that AbortTransaction and AbortSubTransaction can work
 * when we've run out of memory.
 */
static MemoryContext TransactionAbortContext = NULL;

/*
 * List of add-on start- and end-of-xact callbacks
 */
typedef struct XactCallbackItem
{
    struct XactCallbackItem *next;
    XactCallback callback;
    void       *arg;
} XactCallbackItem;

static XactCallbackItem *Xact_callbacks = NULL;

/*
 * List of add-on start- and end-of-subxact callbacks
 */
typedef struct SubXactCallbackItem
{
    struct SubXactCallbackItem *next;
    SubXactCallback callback;
    void       *arg;
} SubXactCallbackItem;

static SubXactCallbackItem *SubXact_callbacks = NULL;


/* local function prototypes */
static void AssignTransactionId(TransactionState s);
static void AbortTransaction(void);
static void AtAbort_Memory(void);
static void AtCleanup_Memory(void);
static void AtAbort_ResourceOwner(void);
static void AtCCI_LocalCache(void);
static void AtCommit_Memory(void);
static void AtStart_Cache(void);
static void AtStart_Memory(void);
static void AtStart_ResourceOwner(void);
static void CallXactCallbacks(XactEvent event);
static void CallSubXactCallbacks(SubXactEvent event,
                     SubTransactionId mySubid,
                     SubTransactionId parentSubid);
static void CleanupTransaction(void);
static void CommitTransaction(void);
static TransactionId RecordTransactionAbort(bool isSubXact);
static void StartTransaction(void);

static void StartSubTransaction(void);
static void CommitSubTransaction(void);
static void AbortSubTransaction(void);
static void CleanupSubTransaction(void);
static void PushTransaction(void);
static void PopTransaction(void);

static void AtSubAbort_Memory(void);
static void AtSubCleanup_Memory(void);
static void AtSubAbort_ResourceOwner(void);
static void AtSubCommit_Memory(void);
static void AtSubStart_Memory(void);
static void AtSubStart_ResourceOwner(void);

static void ShowTransactionState(const char *str);
static void ShowTransactionStateRec(TransactionState state);
static const char *BlockStateAsString(TBlockState blockState);
static const char *TransStateAsString(TransState state);


/* ----------------------------------------------------------------
 *  transaction state accessors
 * ----------------------------------------------------------------
 */

/*
 *  IsTransactionState
 *
 *  This returns true if we are inside a valid transaction; that is,
 *  it is safe to initiate database access, take heavyweight locks, etc.
 */
bool
IsTransactionState(void)
{
    TransactionState s = CurrentTransactionState;

    /*
     * TRANS_DEFAULT and TRANS_ABORT are obviously unsafe states.  However, we
     * also reject the startup/shutdown states TRANS_START, TRANS_COMMIT,
     * TRANS_PREPARE since it might be too soon or too late within those
     * transition states to do anything interesting.  Hence, the only "valid"
     * state is TRANS_INPROGRESS.
     */
    return (s->state == TRANS_INPROGRESS);
}

/*
 *  IsAbortedTransactionBlockState
 *
 *  This returns true if we are within an aborted transaction block.
 */
bool
IsAbortedTransactionBlockState(void)
{
    TransactionState s = CurrentTransactionState;

    if (s->blockState == TBLOCK_ABORT ||
        s->blockState == TBLOCK_SUBABORT)
        return true;

    return false;
}


/*
 *  GetTopTransactionId
 *
 * This will return the XID of the main transaction, assigning one if
 * it's not yet set.  Be careful to call this only inside a valid xact.
 */
TransactionId
GetTopTransactionId(void)
{
    if (!TransactionIdIsValid(TopTransactionStateData.transactionId))
        AssignTransactionId(&TopTransactionStateData);
    return TopTransactionStateData.transactionId;
}

/*
 *  GetTopTransactionIdIfAny
 *
 * This will return the XID of the main transaction, if one is assigned.
 * It will return InvalidTransactionId if we are not currently inside a
 * transaction, or inside a transaction that hasn't yet been assigned an XID.
 */
TransactionId
GetTopTransactionIdIfAny(void)
{
    return TopTransactionStateData.transactionId;
}

/*
 *  GetCurrentTransactionId
 *
 * This will return the XID of the current transaction (main or sub
 * transaction), assigning one if it's not yet set.  Be careful to call this
 * only inside a valid xact.
 */
TransactionId
GetCurrentTransactionId(void)
{
    TransactionState s = CurrentTransactionState;

    if (!TransactionIdIsValid(s->transactionId))
        AssignTransactionId(s);
    return s->transactionId;
}

/*
 *  GetCurrentTransactionIdIfAny
 *
 * This will return the XID of the current sub xact, if one is assigned.
 * It will return InvalidTransactionId if we are not currently inside a
 * transaction, or inside a transaction that hasn't been assigned an XID yet.
 */
TransactionId
GetCurrentTransactionIdIfAny(void)
{
    return CurrentTransactionState->transactionId;
}

/*
 *  GetStableLatestTransactionId
 *
 * Get the transaction's XID if it has one, else read the next-to-be-assigned
 * XID.  Once we have a value, return that same value for the remainder of the
 * current transaction.  This is meant to provide the reference point for the
 * age(xid) function, but might be useful for other maintenance tasks as well.
 */
TransactionId
GetStableLatestTransactionId(void)
{
    static LocalTransactionId lxid = InvalidLocalTransactionId;
    static TransactionId stablexid = InvalidTransactionId;

    if (lxid != MyProc->lxid)
    {
        lxid = MyProc->lxid;
        stablexid = GetTopTransactionIdIfAny();
        if (!TransactionIdIsValid(stablexid))
            stablexid = ReadNewTransactionId();
    }

    Assert(TransactionIdIsValid(stablexid));

    return stablexid;
}

/*
 * AssignTransactionId
 *
 * Assigns a new permanent XID to the given TransactionState.
 * We do not assign XIDs to transactions until/unless this is called.
 * Also, any parent TransactionStates that don't yet have XIDs are assigned
 * one; this maintains the invariant that a child transaction has an XID
 * following its parent's.
 */
static void
AssignTransactionId(TransactionState s)
{
    bool        isSubXact = (s->parent != NULL);
    ResourceOwner currentOwner;

    /* Assert that caller didn't screw up */
    Assert(!TransactionIdIsValid(s->transactionId));
    Assert(s->state == TRANS_INPROGRESS);

    /*
     * Ensure parent(s) have XIDs, so that a child always has an XID later
     * than its parent.  Musn't recurse here, or we might get a stack overflow
     * if we're at the bottom of a huge stack of subtransactions none of which
     * have XIDs yet.
     */
    if (isSubXact && !TransactionIdIsValid(s->parent->transactionId))
    {
        TransactionState p = s->parent;
        TransactionState *parents;
        size_t      parentOffset = 0;

        parents = palloc(sizeof(TransactionState) * s->nestingLevel);
        while (p != NULL && !TransactionIdIsValid(p->transactionId))
        {
            parents[parentOffset++] = p;
            p = p->parent;
        }

        /*
         * This is technically a recursive call, but the recursion will never
         * be more than one layer deep.
         */
        while (parentOffset != 0)
            AssignTransactionId(parents[--parentOffset]);

        pfree(parents);
    }

    /*
     * Generate a new Xid and record it in PG_PROC and pg_subtrans.
     *
     * NB: we must make the subtrans entry BEFORE the Xid appears anywhere in
     * shared storage other than PG_PROC; because if there's no room for it in
     * PG_PROC, the subtrans entry is needed to ensure that other backends see
     * the Xid as "running".  See GetNewTransactionId.
     */
    s->transactionId = GetNewTransactionId(isSubXact);

    if (isSubXact)
        SubTransSetParent(s->transactionId, s->parent->transactionId, false);

    /*
     * If it's a top-level transaction, the predicate locking system needs to
     * be told about it too.
     */
    if (!isSubXact)
        RegisterPredicateLockingXid(s->transactionId);

    /*
     * Acquire lock on the transaction XID.  (We assume this cannot block.) We
     * have to ensure that the lock is assigned to the transaction's own
     * ResourceOwner.
     */
    currentOwner = CurrentResourceOwner;
    PG_TRY();
    {
        CurrentResourceOwner = s->curTransactionOwner;
        XactLockTableInsert(s->transactionId);
    }
    PG_CATCH();
    {
        /* Ensure CurrentResourceOwner is restored on error */
        CurrentResourceOwner = currentOwner;
        PG_RE_THROW();
    }
    PG_END_TRY();
    CurrentResourceOwner = currentOwner;

    /*
     * Every PGPROC_MAX_CACHED_SUBXIDS assigned transaction ids within each
     * top-level transaction we issue a WAL record for the assignment. We
     * include the top-level xid and all the subxids that have not yet been
     * reported using XLOG_XACT_ASSIGNMENT records.
     *
     * This is required to limit the amount of shared memory required in a hot
     * standby server to keep track of in-progress XIDs. See notes for
     * RecordKnownAssignedTransactionIds().
     *
     * We don't keep track of the immediate parent of each subxid, only the
     * top-level transaction that each subxact belongs to. This is correct in
     * recovery only because aborted subtransactions are separately WAL
     * logged.
     */
    if (isSubXact && XLogStandbyInfoActive())
    {
        unreportedXids[nUnreportedXids] = s->transactionId;
        nUnreportedXids++;

        /*
         * ensure this test matches similar one in
         * RecoverPreparedTransactions()
         */
        if (nUnreportedXids >= PGPROC_MAX_CACHED_SUBXIDS)
        {
            XLogRecData rdata[2];
            xl_xact_assignment xlrec;

            /*
             * xtop is always set by now because we recurse up transaction
             * stack to the highest unassigned xid and then come back down
             */
            xlrec.xtop = GetTopTransactionId();
            Assert(TransactionIdIsValid(xlrec.xtop));
            xlrec.nsubxacts = nUnreportedXids;

            rdata[0].data = (char *) &xlrec;
            rdata[0].len = MinSizeOfXactAssignment;
            rdata[0].buffer = InvalidBuffer;
            rdata[0].next = &rdata[1];

            rdata[1].data = (char *) unreportedXids;
            rdata[1].len = PGPROC_MAX_CACHED_SUBXIDS * sizeof(TransactionId);
            rdata[1].buffer = InvalidBuffer;
            rdata[1].next = NULL;

            (void) XLogInsert(RM_XACT_ID, XLOG_XACT_ASSIGNMENT, rdata);

            nUnreportedXids = 0;
        }
    }
}

/*
 *  GetCurrentSubTransactionId
 */
SubTransactionId
GetCurrentSubTransactionId(void)
{
    TransactionState s = CurrentTransactionState;

    return s->subTransactionId;
}

/*
 *  SubTransactionIsActive
 *
 * Test if the specified subxact ID is still active.  Note caller is
 * responsible for checking whether this ID is relevant to the current xact.
 */
bool
SubTransactionIsActive(SubTransactionId subxid)
{
    TransactionState s;

    for (s = CurrentTransactionState; s != NULL; s = s->parent)
    {
        if (s->state == TRANS_ABORT)
            continue;
        if (s->subTransactionId == subxid)
            return true;
    }
    return false;
}


/*
 *  GetCurrentCommandId
 *
 * "used" must be TRUE if the caller intends to use the command ID to mark
 * inserted/updated/deleted tuples.  FALSE means the ID is being fetched
 * for read-only purposes (ie, as a snapshot validity cutoff).  See
 * CommandCounterIncrement() for discussion.
 */
CommandId
GetCurrentCommandId(bool used)
{
    /* this is global to a transaction, not subtransaction-local */
    if (used)
        currentCommandIdUsed = true;
    return currentCommandId;
}

/*
 *  GetCurrentTransactionStartTimestamp
 */
TimestampTz
GetCurrentTransactionStartTimestamp(void)
{
    return xactStartTimestamp;
}

/*
 *  GetCurrentStatementStartTimestamp
 */
TimestampTz
GetCurrentStatementStartTimestamp(void)
{
    return stmtStartTimestamp;
}

/*
 *  GetCurrentTransactionStopTimestamp
 *
 * We return current time if the transaction stop time hasn't been set
 * (which can happen if we decide we don't need to log an XLOG record).
 */
TimestampTz
GetCurrentTransactionStopTimestamp(void)
{
    if (xactStopTimestamp != 0)
        return xactStopTimestamp;
    return GetCurrentTimestamp();
}

/*
 *  SetCurrentStatementStartTimestamp
 */
void
SetCurrentStatementStartTimestamp(void)
{
    stmtStartTimestamp = GetCurrentTimestamp();
}

/*
 *  SetCurrentTransactionStopTimestamp
 */
static inline void
SetCurrentTransactionStopTimestamp(void)
{
    xactStopTimestamp = GetCurrentTimestamp();
}

/*
 *  GetCurrentTransactionNestLevel
 *
 * Note: this will return zero when not inside any transaction, one when
 * inside a top-level transaction, etc.
 */
int
GetCurrentTransactionNestLevel(void)
{
    TransactionState s = CurrentTransactionState;

    return s->nestingLevel;
}


/*
 *  TransactionIdIsCurrentTransactionId
 */
bool
TransactionIdIsCurrentTransactionId(TransactionId xid)
{
    TransactionState s;

    /*
     * We always say that BootstrapTransactionId is "not my transaction ID"
     * even when it is (ie, during bootstrap).  Along with the fact that
     * transam.c always treats BootstrapTransactionId as already committed,
     * this causes the tqual.c routines to see all tuples as committed, which
     * is what we need during bootstrap.  (Bootstrap mode only inserts tuples,
     * it never updates or deletes them, so all tuples can be presumed good
     * immediately.)
     *
     * Likewise, InvalidTransactionId and FrozenTransactionId are certainly
     * not my transaction ID, so we can just return "false" immediately for
     * any non-normal XID.
     */
    if (!TransactionIdIsNormal(xid))
        return false;

    /*
     * We will return true for the Xid of the current subtransaction, any of
     * its subcommitted children, any of its parents, or any of their
     * previously subcommitted children.  However, a transaction being aborted
     * is no longer "current", even though it may still have an entry on the
     * state stack.
     */
    for (s = CurrentTransactionState; s != NULL; s = s->parent)
    {
        int         low,
                    high;

        if (s->state == TRANS_ABORT)
            continue;
        if (!TransactionIdIsValid(s->transactionId))
            continue;           /* it can't have any child XIDs either */
        if (TransactionIdEquals(xid, s->transactionId))
            return true;
        /* As the childXids array is ordered, we can use binary search */
        low = 0;
        high = s->nChildXids - 1;
        while (low <= high)
        {
            int         middle;
            TransactionId probe;

            middle = low + (high - low) / 2;
            probe = s->childXids[middle];
            if (TransactionIdEquals(probe, xid))
                return true;
            else if (TransactionIdPrecedes(probe, xid))
                low = middle + 1;
            else
                high = middle - 1;
        }
    }

    return false;
}

/*
 *  TransactionStartedDuringRecovery
 *
 * Returns true if the current transaction started while recovery was still
 * in progress. Recovery might have ended since so RecoveryInProgress() might
 * return false already.
 */
bool
TransactionStartedDuringRecovery(void)
{
    return CurrentTransactionState->startedInRecovery;
}

/*
 *  CommandCounterIncrement
 */
void
CommandCounterIncrement(void)
{
    /*
     * If the current value of the command counter hasn't been "used" to mark
     * tuples, we need not increment it, since there's no need to distinguish
     * a read-only command from others.  This helps postpone command counter
     * overflow, and keeps no-op CommandCounterIncrement operations cheap.
     */
    if (currentCommandIdUsed)
    {
        currentCommandId += 1;
        if (currentCommandId == FirstCommandId) /* check for overflow */
        {
            currentCommandId -= 1;
            ereport(ERROR,
                    (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                     errmsg("cannot have more than 2^32-1 commands in a transaction")));
        }
        currentCommandIdUsed = false;

        /* Propagate new command ID into static snapshots */
        SnapshotSetCommandId(currentCommandId);

        /*
         * Make any catalog changes done by the just-completed command visible
         * in the local syscache.  We obviously don't need to do this after a
         * read-only command.  (But see hacks in inval.c to make real sure we
         * don't think a command that queued inval messages was read-only.)
         */
        AtCCI_LocalCache();
    }
}

/*
 * ForceSyncCommit
 *
 * Interface routine to allow commands to force a synchronous commit of the
 * current top-level transaction
 */
void
ForceSyncCommit(void)
{
    forceSyncCommit = true;
}


/* ----------------------------------------------------------------
 *                      StartTransaction stuff
 * ----------------------------------------------------------------
 */

/*
 *  AtStart_Cache
 */
static void
AtStart_Cache(void)
{
    AcceptInvalidationMessages();
}

/*
 *  AtStart_Memory
 */
static void
AtStart_Memory(void)
{
    TransactionState s = CurrentTransactionState;

    /*
     * If this is the first time through, create a private context for
     * AbortTransaction to work in.  By reserving some space now, we can
     * insulate AbortTransaction from out-of-memory scenarios.  Like
     * ErrorContext, we set it up with slow growth rate and a nonzero minimum
     * size, so that space will be reserved immediately.
     */
    if (TransactionAbortContext == NULL)
        TransactionAbortContext =
            AllocSetContextCreate(TopMemoryContext,
                                  "TransactionAbortContext",
                                  32 * 1024,
                                  32 * 1024,
                                  32 * 1024);

    /*
     * We shouldn't have a transaction context already.
     */
    Assert(TopTransactionContext == NULL);

    /*
     * Create a toplevel context for the transaction.
     */
    TopTransactionContext =
        AllocSetContextCreate(TopMemoryContext,
                              "TopTransactionContext",
                              ALLOCSET_DEFAULT_MINSIZE,
                              ALLOCSET_DEFAULT_INITSIZE,
                              ALLOCSET_DEFAULT_MAXSIZE);

    /*
     * In a top-level transaction, CurTransactionContext is the same as
     * TopTransactionContext.
     */
    CurTransactionContext = TopTransactionContext;
    s->curTransactionContext = CurTransactionContext;

    /* Make the CurTransactionContext active. */
    MemoryContextSwitchTo(CurTransactionContext);
}

/*
 *  AtStart_ResourceOwner
 */
static void
AtStart_ResourceOwner(void)
{
    TransactionState s = CurrentTransactionState;

    /*
     * We shouldn't have a transaction resource owner already.
     */
    Assert(TopTransactionResourceOwner == NULL);

    /*
     * Create a toplevel resource owner for the transaction.
     */
    s->curTransactionOwner = ResourceOwnerCreate(NULL, "TopTransaction");

    TopTransactionResourceOwner = s->curTransactionOwner;
    CurTransactionResourceOwner = s->curTransactionOwner;
    CurrentResourceOwner = s->curTransactionOwner;
}

/* ----------------------------------------------------------------
 *                      StartSubTransaction stuff
 * ----------------------------------------------------------------
 */

/*
 * AtSubStart_Memory
 */
static void
AtSubStart_Memory(void)
{
    TransactionState s = CurrentTransactionState;

    Assert(CurTransactionContext != NULL);

    /*
     * Create a CurTransactionContext, which will be used to hold data that
     * survives subtransaction commit but disappears on subtransaction abort.
     * We make it a child of the immediate parent's CurTransactionContext.
     */
    CurTransactionContext = AllocSetContextCreate(CurTransactionContext,
                                                  "CurTransactionContext",
                                                  ALLOCSET_DEFAULT_MINSIZE,
                                                  ALLOCSET_DEFAULT_INITSIZE,
                                                  ALLOCSET_DEFAULT_MAXSIZE);
    s->curTransactionContext = CurTransactionContext;

    /* Make the CurTransactionContext active. */
    MemoryContextSwitchTo(CurTransactionContext);
}

/*
 * AtSubStart_ResourceOwner
 */
static void
AtSubStart_ResourceOwner(void)
{
    TransactionState s = CurrentTransactionState;

    Assert(s->parent != NULL);

    /*
     * Create a resource owner for the subtransaction.  We make it a child of
     * the immediate parent's resource owner.
     */
    s->curTransactionOwner =
        ResourceOwnerCreate(s->parent->curTransactionOwner,
                            "SubTransaction");

    CurTransactionResourceOwner = s->curTransactionOwner;
    CurrentResourceOwner = s->curTransactionOwner;
}

/* ----------------------------------------------------------------
 *                      CommitTransaction stuff
 * ----------------------------------------------------------------
 */

/*
 *  RecordTransactionCommit
 *
 * Returns latest XID among xact and its children, or InvalidTransactionId
 * if the xact has no XID.  (We compute that here just because it's easier.)
 */
static TransactionId
RecordTransactionCommit(void)
{
    TransactionId xid = GetTopTransactionIdIfAny();
    bool        markXidCommitted = TransactionIdIsValid(xid);
    TransactionId latestXid = InvalidTransactionId;
    int         nrels;
    RelFileNode *rels;
    int         nchildren;
    TransactionId *children;
    int         nmsgs = 0;
    SharedInvalidationMessage *invalMessages = NULL;
    bool        RelcacheInitFileInval = false;
    bool        wrote_xlog;

    /* Get data needed for commit record */
    nrels = smgrGetPendingDeletes(true, &rels);
    nchildren = xactGetCommittedChildren(&children);
    if (XLogStandbyInfoActive())
        nmsgs = xactGetCommittedInvalidationMessages(&invalMessages,
                                                     &RelcacheInitFileInval);
    wrote_xlog = (XactLastRecEnd != 0);

    /*
     * If we haven't been assigned an XID yet, we neither can, nor do we want
     * to write a COMMIT record.
     */
    if (!markXidCommitted)
    {
        /*
         * We expect that every smgrscheduleunlink is followed by a catalog
         * update, and hence XID assignment, so we shouldn't get here with any
         * pending deletes.  Use a real test not just an Assert to check this,
         * since it's a bit fragile.
         */
        if (nrels != 0)
            elog(ERROR, "cannot commit a transaction that deleted files but has no xid");

        /* Can't have child XIDs either; AssignTransactionId enforces this */
        Assert(nchildren == 0);

        /*
         * If we didn't create XLOG entries, we're done here; otherwise we
         * should flush those entries the same as a commit record.  (An
         * example of a possible record that wouldn't cause an XID to be
         * assigned is a sequence advance record due to nextval() --- we want
         * to flush that to disk before reporting commit.)
         */
        if (!wrote_xlog)
            goto cleanup;
    }
    else
    {
        /*
         * Begin commit critical section and insert the commit XLOG record.
         */
        /* Tell bufmgr and smgr to prepare for commit */
        BufmgrCommit();

        /*
         * Mark ourselves as within our "commit critical section".  This
         * forces any concurrent checkpoint to wait until we've updated
         * pg_clog.  Without this, it is possible for the checkpoint to set
         * REDO after the XLOG record but fail to flush the pg_clog update to
         * disk, leading to loss of the transaction commit if the system
         * crashes a little later.
         *
         * Note: we could, but don't bother to, set this flag in
         * RecordTransactionAbort.  That's because loss of a transaction abort
         * is noncritical; the presumption would be that it aborted, anyway.
         *
         * It's safe to change the delayChkpt flag of our own backend without
         * holding the ProcArrayLock, since we're the only one modifying it.
         * This makes checkpoint's determination of which xacts are delayChkpt a
         * bit fuzzy, but it doesn't matter.
         */
        START_CRIT_SECTION();
        MyPgXact->delayChkpt = true;

        SetCurrentTransactionStopTimestamp();

        /*
         * Do we need the long commit record? If not, use the compact format.
         */
        if (nrels > 0 || nmsgs > 0 || RelcacheInitFileInval || forceSyncCommit)
        {
            XLogRecData rdata[4];
            int         lastrdata = 0;
            xl_xact_commit xlrec;

            /*
             * Set flags required for recovery processing of commits.
             */
            xlrec.xinfo = 0;
            if (RelcacheInitFileInval)
                xlrec.xinfo |= XACT_COMPLETION_UPDATE_RELCACHE_FILE;
            if (forceSyncCommit)
                xlrec.xinfo |= XACT_COMPLETION_FORCE_SYNC_COMMIT;

            xlrec.dbId = MyDatabaseId;
            xlrec.tsId = MyDatabaseTableSpace;

            xlrec.xact_time = xactStopTimestamp;
            xlrec.nrels = nrels;
            xlrec.nsubxacts = nchildren;
            xlrec.nmsgs = nmsgs;
            rdata[0].data = (char *) (&xlrec);
            rdata[0].len = MinSizeOfXactCommit;
            rdata[0].buffer = InvalidBuffer;
            /* dump rels to delete */
            if (nrels > 0)
            {
                rdata[0].next = &(rdata[1]);
                rdata[1].data = (char *) rels;
                rdata[1].len = nrels * sizeof(RelFileNode);
                rdata[1].buffer = InvalidBuffer;
                lastrdata = 1;
            }
            /* dump committed child Xids */
            if (nchildren > 0)
            {
                rdata[lastrdata].next = &(rdata[2]);
                rdata[2].data = (char *) children;
                rdata[2].len = nchildren * sizeof(TransactionId);
                rdata[2].buffer = InvalidBuffer;
                lastrdata = 2;
            }
            /* dump shared cache invalidation messages */
            if (nmsgs > 0)
            {
                rdata[lastrdata].next = &(rdata[3]);
                rdata[3].data = (char *) invalMessages;
                rdata[3].len = nmsgs * sizeof(SharedInvalidationMessage);
                rdata[3].buffer = InvalidBuffer;
                lastrdata = 3;
            }
            rdata[lastrdata].next = NULL;

            (void) XLogInsert(RM_XACT_ID, XLOG_XACT_COMMIT, rdata);
        }
        else
        {
            XLogRecData rdata[2];
            int         lastrdata = 0;
            xl_xact_commit_compact xlrec;

            xlrec.xact_time = xactStopTimestamp;
            xlrec.nsubxacts = nchildren;
            rdata[0].data = (char *) (&xlrec);
            rdata[0].len = MinSizeOfXactCommitCompact;
            rdata[0].buffer = InvalidBuffer;
            /* dump committed child Xids */
            if (nchildren > 0)
            {
                rdata[0].next = &(rdata[1]);
                rdata[1].data = (char *) children;
                rdata[1].len = nchildren * sizeof(TransactionId);
                rdata[1].buffer = InvalidBuffer;
                lastrdata = 1;
            }
            rdata[lastrdata].next = NULL;

            (void) XLogInsert(RM_XACT_ID, XLOG_XACT_COMMIT_COMPACT, rdata);
        }
    }

    /*
     * Check if we want to commit asynchronously.  We can allow the XLOG flush
     * to happen asynchronously if synchronous_commit=off, or if the current
     * transaction has not performed any WAL-logged operation.  The latter
     * case can arise if the current transaction wrote only to temporary
     * and/or unlogged tables.  In case of a crash, the loss of such a
     * transaction will be irrelevant since temp tables will be lost anyway,
     * and unlogged tables will be truncated.  (Given the foregoing, you might
     * think that it would be unnecessary to emit the XLOG record at all in
     * this case, but we don't currently try to do that.  It would certainly
     * cause problems at least in Hot Standby mode, where the
     * KnownAssignedXids machinery requires tracking every XID assignment.  It
     * might be OK to skip it only when wal_level < hot_standby, but for now
     * we don't.)
     *
     * However, if we're doing cleanup of any non-temp rels or committing any
     * command that wanted to force sync commit, then we must flush XLOG
     * immediately.  (We must not allow asynchronous commit if there are any
     * non-temp tables to be deleted, because we might delete the files before
     * the COMMIT record is flushed to disk.  We do allow asynchronous commit
     * if all to-be-deleted tables are temporary though, since they are lost
     * anyway if we crash.)
     */
    if ((wrote_xlog && synchronous_commit > SYNCHRONOUS_COMMIT_OFF) ||
        forceSyncCommit || nrels > 0)
    {
        XLogFlush(XactLastRecEnd);

        /*
         * Now we may update the CLOG, if we wrote a COMMIT record above
         */
        if (markXidCommitted)
            TransactionIdCommitTree(xid, nchildren, children);
    }
    else
    {
        /*
         * Asynchronous commit case:
         *
         * This enables possible committed transaction loss in the case of a
         * postmaster crash because WAL buffers are left unwritten. Ideally we
         * could issue the WAL write without the fsync, but some
         * wal_sync_methods do not allow separate write/fsync.
         *
         * Report the latest async commit LSN, so that the WAL writer knows to
         * flush this commit.
         */
        XLogSetAsyncXactLSN(XactLastRecEnd);

        /*
         * We must not immediately update the CLOG, since we didn't flush the
         * XLOG. Instead, we store the LSN up to which the XLOG must be
         * flushed before the CLOG may be updated.
         */
        if (markXidCommitted)
            TransactionIdAsyncCommitTree(xid, nchildren, children, XactLastRecEnd);
    }

    /*
     * If we entered a commit critical section, leave it now, and let
     * checkpoints proceed.
     */
    if (markXidCommitted)
    {
        MyPgXact->delayChkpt = false;
        END_CRIT_SECTION();
    }

    /* Compute latestXid while we have the child XIDs handy */
    latestXid = TransactionIdLatest(xid, nchildren, children);

    /*
     * Wait for synchronous replication, if required.
     *
     * Note that at this stage we have marked clog, but still show as running
     * in the procarray and continue to hold locks.
     */
    if (wrote_xlog)
        SyncRepWaitForLSN(XactLastRecEnd);

    /* Reset XactLastRecEnd until the next transaction writes something */
    XactLastRecEnd = 0;

cleanup:
    /* Clean up local data */
    if (rels)
        pfree(rels);

    return latestXid;
}


/*
 *  AtCCI_LocalCache
 */
static void
AtCCI_LocalCache(void)
{
    /*
     * Make any pending relation map changes visible.  We must do this before
     * processing local sinval messages, so that the map changes will get
     * reflected into the relcache when relcache invals are processed.
     */
    AtCCI_RelationMap();

    /*
     * Make catalog changes visible to me for the next command.
     */
    CommandEndInvalidationMessages();
}

/*
 *  AtCommit_Memory
 */
static void
AtCommit_Memory(void)
{
    /*
     * Now that we're "out" of a transaction, have the system allocate things
     * in the top memory context instead of per-transaction contexts.
     */
    MemoryContextSwitchTo(TopMemoryContext);

    /*
     * Release all transaction-local memory.
     */
    Assert(TopTransactionContext != NULL);
    MemoryContextDelete(TopTransactionContext);
    TopTransactionContext = NULL;
    CurTransactionContext = NULL;
    CurrentTransactionState->curTransactionContext = NULL;
}

/* ----------------------------------------------------------------
 *                      CommitSubTransaction stuff
 * ----------------------------------------------------------------
 */

/*
 * AtSubCommit_Memory
 */
static void
AtSubCommit_Memory(void)
{
    TransactionState s = CurrentTransactionState;

    Assert(s->parent != NULL);

    /* Return to parent transaction level's memory context. */
    CurTransactionContext = s->parent->curTransactionContext;
    MemoryContextSwitchTo(CurTransactionContext);

    /*
     * Ordinarily we cannot throw away the child's CurTransactionContext,
     * since the data it contains will be needed at upper commit.  However, if
     * there isn't actually anything in it, we can throw it away.  This avoids
     * a small memory leak in the common case of "trivial" subxacts.
     */
    if (MemoryContextIsEmpty(s->curTransactionContext))
    {
        MemoryContextDelete(s->curTransactionContext);
        s->curTransactionContext = NULL;
    }
}

/*
 * AtSubCommit_childXids
 *
 * Pass my own XID and my child XIDs up to my parent as committed children.
 */
static void
AtSubCommit_childXids(void)
{
    TransactionState s = CurrentTransactionState;
    int         new_nChildXids;

    Assert(s->parent != NULL);

    /*
     * The parent childXids array will need to hold my XID and all my
     * childXids, in addition to the XIDs already there.
     */
    new_nChildXids = s->parent->nChildXids + s->nChildXids + 1;

    /* Allocate or enlarge the parent array if necessary */
    if (s->parent->maxChildXids < new_nChildXids)
    {
        int         new_maxChildXids;
        TransactionId *new_childXids;

        /*
         * Make it 2x what's needed right now, to avoid having to enlarge it
         * repeatedly. But we can't go above MaxAllocSize.  (The latter limit
         * is what ensures that we don't need to worry about integer overflow
         * here or in the calculation of new_nChildXids.)
         */
        new_maxChildXids = Min(new_nChildXids * 2,
                               (int) (MaxAllocSize / sizeof(TransactionId)));

        if (new_maxChildXids < new_nChildXids)
            ereport(ERROR,
                    (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                     errmsg("maximum number of committed subtransactions (%d) exceeded",
                            (int) (MaxAllocSize / sizeof(TransactionId)))));

        /*
         * We keep the child-XID arrays in TopTransactionContext; this avoids
         * setting up child-transaction contexts for what might be just a few
         * bytes of grandchild XIDs.
         */
        if (s->parent->childXids == NULL)
            new_childXids =
                MemoryContextAlloc(TopTransactionContext,
                                   new_maxChildXids * sizeof(TransactionId));
        else
            new_childXids = repalloc(s->parent->childXids,
                                   new_maxChildXids * sizeof(TransactionId));

        s->parent->childXids = new_childXids;
        s->parent->maxChildXids = new_maxChildXids;
    }

    /*
     * Copy all my XIDs to parent's array.
     *
     * Note: We rely on the fact that the XID of a child always follows that
     * of its parent.  By copying the XID of this subtransaction before the
     * XIDs of its children, we ensure that the array stays ordered. Likewise,
     * all XIDs already in the array belong to subtransactions started and
     * subcommitted before us, so their XIDs must precede ours.
     */
    s->parent->childXids[s->parent->nChildXids] = s->transactionId;

    if (s->nChildXids > 0)
        memcpy(&s->parent->childXids[s->parent->nChildXids + 1],
               s->childXids,
               s->nChildXids * sizeof(TransactionId));

    s->parent->nChildXids = new_nChildXids;

    /* Release child's array to avoid leakage */
    if (s->childXids != NULL)
        pfree(s->childXids);
    /* We must reset these to avoid double-free if fail later in commit */
    s->childXids = NULL;
    s->nChildXids = 0;
    s->maxChildXids = 0;
}

/* ----------------------------------------------------------------
 *                      AbortTransaction stuff
 * ----------------------------------------------------------------
 */

/*
 *  RecordTransactionAbort
 *
 * Returns latest XID among xact and its children, or InvalidTransactionId
 * if the xact has no XID.  (We compute that here just because it's easier.)
 */
static TransactionId
RecordTransactionAbort(bool isSubXact)
{
    TransactionId xid = GetCurrentTransactionIdIfAny();
    TransactionId latestXid;
    int         nrels;
    RelFileNode *rels;
    int         nchildren;
    TransactionId *children;
    XLogRecData rdata[3];
    int         lastrdata = 0;
    xl_xact_abort xlrec;

    /*
     * If we haven't been assigned an XID, nobody will care whether we aborted
     * or not.  Hence, we're done in that case.  It does not matter if we have
     * rels to delete (note that this routine is not responsible for actually
     * deleting 'em).  We cannot have any child XIDs, either.
     */
    if (!TransactionIdIsValid(xid))
    {
        /* Reset XactLastRecEnd until the next transaction writes something */
        if (!isSubXact)
            XactLastRecEnd = 0;
        return InvalidTransactionId;
    }

    /*
     * We have a valid XID, so we should write an ABORT record for it.
     *
     * We do not flush XLOG to disk here, since the default assumption after a
     * crash would be that we aborted, anyway.  For the same reason, we don't
     * need to worry about interlocking against checkpoint start.
     */

    /*
     * Check that we haven't aborted halfway through RecordTransactionCommit.
     */
    if (TransactionIdDidCommit(xid))
        elog(PANIC, "cannot abort transaction %u, it was already committed",
             xid);

    /* Fetch the data we need for the abort record */
    nrels = smgrGetPendingDeletes(false, &rels);
    nchildren = xactGetCommittedChildren(&children);

    /* XXX do we really need a critical section here? */
    START_CRIT_SECTION();

    /* Write the ABORT record */
    if (isSubXact)
        xlrec.xact_time = GetCurrentTimestamp();
    else
    {
        SetCurrentTransactionStopTimestamp();
        xlrec.xact_time = xactStopTimestamp;
    }
    xlrec.nrels = nrels;
    xlrec.nsubxacts = nchildren;
    rdata[0].data = (char *) (&xlrec);
    rdata[0].len = MinSizeOfXactAbort;
    rdata[0].buffer = InvalidBuffer;
    /* dump rels to delete */
    if (nrels > 0)
    {
        rdata[0].next = &(rdata[1]);
        rdata[1].data = (char *) rels;
        rdata[1].len = nrels * sizeof(RelFileNode);
        rdata[1].buffer = InvalidBuffer;
        lastrdata = 1;
    }
    /* dump committed child Xids */
    if (nchildren > 0)
    {
        rdata[lastrdata].next = &(rdata[2]);
        rdata[2].data = (char *) children;
        rdata[2].len = nchildren * sizeof(TransactionId);
        rdata[2].buffer = InvalidBuffer;
        lastrdata = 2;
    }
    rdata[lastrdata].next = NULL;

    (void) XLogInsert(RM_XACT_ID, XLOG_XACT_ABORT, rdata);

    /*
     * Report the latest async abort LSN, so that the WAL writer knows to
     * flush this abort. There's nothing to be gained by delaying this, since
     * WALWriter may as well do this when it can. This is important with
     * streaming replication because if we don't flush WAL regularly we will
     * find that large aborts leave us with a long backlog for when commits
     * occur after the abort, increasing our window of data loss should
     * problems occur at that point.
     */
    if (!isSubXact)
        XLogSetAsyncXactLSN(XactLastRecEnd);

    /*
     * Mark the transaction aborted in clog.  This is not absolutely necessary
     * but we may as well do it while we are here; also, in the subxact case
     * it is helpful because XactLockTableWait makes use of it to avoid
     * waiting for already-aborted subtransactions.  It is OK to do it without
     * having flushed the ABORT record to disk, because in event of a crash
     * we'd be assumed to have aborted anyway.
     */
    TransactionIdAbortTree(xid, nchildren, children);

    END_CRIT_SECTION();

    /* Compute latestXid while we have the child XIDs handy */
    latestXid = TransactionIdLatest(xid, nchildren, children);

    /*
     * If we're aborting a subtransaction, we can immediately remove failed
     * XIDs from PGPROC's cache of running child XIDs.  We do that here for
     * subxacts, because we already have the child XID array at hand.  For
     * main xacts, the equivalent happens just after this function returns.
     */
    if (isSubXact)
        XidCacheRemoveRunningXids(xid, nchildren, children, latestXid);

    /* Reset XactLastRecEnd until the next transaction writes something */
    if (!isSubXact)
        XactLastRecEnd = 0;

    /* And clean up local data */
    if (rels)
        pfree(rels);

    return latestXid;
}

/*
 *  AtAbort_Memory
 */
static void
AtAbort_Memory(void)
{
    /*
     * Switch into TransactionAbortContext, which should have some free space
     * even if nothing else does.  We'll work in this context until we've
     * finished cleaning up.
     *
     * It is barely possible to get here when we've not been able to create
     * TransactionAbortContext yet; if so use TopMemoryContext.
     */
    if (TransactionAbortContext != NULL)
        MemoryContextSwitchTo(TransactionAbortContext);
    else
        MemoryContextSwitchTo(TopMemoryContext);
}

/*
 * AtSubAbort_Memory
 */
static void
AtSubAbort_Memory(void)
{
    Assert(TransactionAbortContext != NULL);

    MemoryContextSwitchTo(TransactionAbortContext);
}


/*
 *  AtAbort_ResourceOwner
 */
static void
AtAbort_ResourceOwner(void)
{
    /*
     * Make sure we have a valid ResourceOwner, if possible (else it will be
     * NULL, which is OK)
     */
    CurrentResourceOwner = TopTransactionResourceOwner;
}

/*
 * AtSubAbort_ResourceOwner
 */
static void
AtSubAbort_ResourceOwner(void)
{
    TransactionState s = CurrentTransactionState;

    /* Make sure we have a valid ResourceOwner */
    CurrentResourceOwner = s->curTransactionOwner;
}


/*
 * AtSubAbort_childXids
 */
static void
AtSubAbort_childXids(void)
{
    TransactionState s = CurrentTransactionState;

    /*
     * We keep the child-XID arrays in TopTransactionContext (see
     * AtSubCommit_childXids).  This means we'd better free the array
     * explicitly at abort to avoid leakage.
     */
    if (s->childXids != NULL)
        pfree(s->childXids);
    s->childXids = NULL;
    s->nChildXids = 0;
    s->maxChildXids = 0;

    /*
     * We could prune the unreportedXids array here. But we don't bother. That
     * would potentially reduce number of XLOG_XACT_ASSIGNMENT records but it
     * would likely introduce more CPU time into the more common paths, so we
     * choose not to do that.
     */
}

/* ----------------------------------------------------------------
 *                      CleanupTransaction stuff
 * ----------------------------------------------------------------
 */

/*
 *  AtCleanup_Memory
 */
static void
AtCleanup_Memory(void)
{
    Assert(CurrentTransactionState->parent == NULL);

    /*
     * Now that we're "out" of a transaction, have the system allocate things
     * in the top memory context instead of per-transaction contexts.
     */
    MemoryContextSwitchTo(TopMemoryContext);

    /*
     * Clear the special abort context for next time.
     */
    if (TransactionAbortContext != NULL)
        MemoryContextResetAndDeleteChildren(TransactionAbortContext);

    /*
     * Release all transaction-local memory.
     */
    if (TopTransactionContext != NULL)
        MemoryContextDelete(TopTransactionContext);
    TopTransactionContext = NULL;
    CurTransactionContext = NULL;
    CurrentTransactionState->curTransactionContext = NULL;
}


/* ----------------------------------------------------------------
 *                      CleanupSubTransaction stuff
 * ----------------------------------------------------------------
 */

/*
 * AtSubCleanup_Memory
 */
static void
AtSubCleanup_Memory(void)
{
    TransactionState s = CurrentTransactionState;

    Assert(s->parent != NULL);

    /* Make sure we're not in an about-to-be-deleted context */
    MemoryContextSwitchTo(s->parent->curTransactionContext);
    CurTransactionContext = s->parent->curTransactionContext;

    /*
     * Clear the special abort context for next time.
     */
    if (TransactionAbortContext != NULL)
        MemoryContextResetAndDeleteChildren(TransactionAbortContext);

    /*
     * Delete the subxact local memory contexts. Its CurTransactionContext can
     * go too (note this also kills CurTransactionContexts from any children
     * of the subxact).
     */
    if (s->curTransactionContext)
        MemoryContextDelete(s->curTransactionContext);
    s->curTransactionContext = NULL;
}

/* ----------------------------------------------------------------
 *                      interface routines
 * ----------------------------------------------------------------
 */

/*
 *  StartTransaction
 */
static void
StartTransaction(void)
{
    TransactionState s;
    VirtualTransactionId vxid;

    /*
     * Let's just make sure the state stack is empty
     */
    s = &TopTransactionStateData;
    CurrentTransactionState = s;

    /*
     * check the current transaction state
     */
    if (s->state != TRANS_DEFAULT)
        elog(WARNING, "StartTransaction while in %s state",
             TransStateAsString(s->state));

    /*
     * set the current transaction state information appropriately during
     * start processing
     */
    s->state = TRANS_START;
    s->transactionId = InvalidTransactionId;    /* until assigned */

    /*
     * Make sure we've reset xact state variables
     *
     * If recovery is still in progress, mark this transaction as read-only.
     * We have lower level defences in XLogInsert and elsewhere to stop us
     * from modifying data during recovery, but this gives the normal
     * indication to the user that the transaction is read-only.
     */
    if (RecoveryInProgress())
    {
        s->startedInRecovery = true;
        XactReadOnly = true;
    }
    else
    {
        s->startedInRecovery = false;
        XactReadOnly = DefaultXactReadOnly;
    }
    XactDeferrable = DefaultXactDeferrable;
    XactIsoLevel = DefaultXactIsoLevel;
    forceSyncCommit = false;
    MyXactAccessedTempRel = false;

    /*
     * reinitialize within-transaction counters
     */
    s->subTransactionId = TopSubTransactionId;
    currentSubTransactionId = TopSubTransactionId;
    currentCommandId = FirstCommandId;
    currentCommandIdUsed = false;

    /*
     * initialize reported xid accounting
     */
    nUnreportedXids = 0;

    /*
     * must initialize resource-management stuff first
     */
    AtStart_Memory();
    AtStart_ResourceOwner();

    /*
     * Assign a new LocalTransactionId, and combine it with the backendId to
     * form a virtual transaction id.
     */
    vxid.backendId = MyBackendId;
    vxid.localTransactionId = GetNextLocalTransactionId();

    /*
     * Lock the virtual transaction id before we announce it in the proc array
     */
    VirtualXactLockTableInsert(vxid);

    /*
     * Advertise it in the proc array.  We assume assignment of
     * LocalTransactionID is atomic, and the backendId should be set already.
     */
    Assert(MyProc->backendId == vxid.backendId);
    MyProc->lxid = vxid.localTransactionId;

    TRACE_POSTGRESQL_TRANSACTION_START(vxid.localTransactionId);

    /*
     * set transaction_timestamp() (a/k/a now()).  We want this to be the same
     * as the first command's statement_timestamp(), so don't do a fresh
     * GetCurrentTimestamp() call (which'd be expensive anyway).  Also, mark
     * xactStopTimestamp as unset.
     */
    xactStartTimestamp = stmtStartTimestamp;
    xactStopTimestamp = 0;
    pgstat_report_xact_timestamp(xactStartTimestamp);

    /*
     * initialize current transaction state fields
     *
     * note: prevXactReadOnly is not used at the outermost level
     */
    s->nestingLevel = 1;
    s->gucNestLevel = 1;
    s->childXids = NULL;
    s->nChildXids = 0;
    s->maxChildXids = 0;
    GetUserIdAndSecContext(&s->prevUser, &s->prevSecContext);
    /* SecurityRestrictionContext should never be set outside a transaction */
    Assert(s->prevSecContext == 0);

    /*
     * initialize other subsystems for new transaction
     */
    AtStart_GUC();
    AtStart_Inval();
    AtStart_Cache();
    AfterTriggerBeginXact();

    /*
     * done with start processing, set current transaction state to "in
     * progress"
     */
    s->state = TRANS_INPROGRESS;

    ShowTransactionState("StartTransaction");
}


/*
 *  CommitTransaction
 *
 * NB: if you change this routine, better look at PrepareTransaction too!
 */
static void
CommitTransaction(void)
{
    TransactionState s = CurrentTransactionState;
    TransactionId latestXid;

    ShowTransactionState("CommitTransaction");

    /*
     * check the current transaction state
     */
    if (s->state != TRANS_INPROGRESS)
        elog(WARNING, "CommitTransaction while in %s state",
             TransStateAsString(s->state));
    Assert(s->parent == NULL);

    /*
     * Do pre-commit processing that involves calling user-defined code, such
     * as triggers.  Since closing cursors could queue trigger actions,
     * triggers could open cursors, etc, we have to keep looping until there's
     * nothing left to do.
     */
    for (;;)
    {
        /*
         * Fire all currently pending deferred triggers.
         */
        AfterTriggerFireDeferred();

        /*
         * Close open portals (converting holdable ones into static portals).
         * If there weren't any, we are done ... otherwise loop back to check
         * if they queued deferred triggers.  Lather, rinse, repeat.
         */
        if (!PreCommit_Portals(false))
            break;
    }

    CallXactCallbacks(XACT_EVENT_PRE_COMMIT);

    /*
     * The remaining actions cannot call any user-defined code, so it's safe
     * to start shutting down within-transaction services.  But note that most
     * of this stuff could still throw an error, which would switch us into
     * the transaction-abort path.
     */

    /* Shut down the deferred-trigger manager */
    AfterTriggerEndXact(true);

    /*
     * Let ON COMMIT management do its thing (must happen after closing
     * cursors, to avoid dangling-reference problems)
     */
    PreCommit_on_commit_actions();

    /* close large objects before lower-level cleanup */
    AtEOXact_LargeObject(true);

    /*
     * Mark serializable transaction as complete for predicate locking
     * purposes.  This should be done as late as we can put it and still allow
     * errors to be raised for failure patterns found at commit.
     */
    PreCommit_CheckForSerializationFailure();

    /*
     * Insert notifications sent by NOTIFY commands into the queue.  This
     * should be late in the pre-commit sequence to minimize time spent
     * holding the notify-insertion lock.
     */
    PreCommit_Notify();

    /* Prevent cancel/die interrupt while cleaning up */
    HOLD_INTERRUPTS();

    /* Commit updates to the relation map --- do this as late as possible */
    AtEOXact_RelationMap(true);

    /*
     * set the current transaction state information appropriately during
     * commit processing
     */
    s->state = TRANS_COMMIT;

    /*
     * Here is where we really truly commit.
     */
    latestXid = RecordTransactionCommit();

    TRACE_POSTGRESQL_TRANSACTION_COMMIT(MyProc->lxid);

    /*
     * Let others know about no transaction in progress by me. Note that this
     * must be done _before_ releasing locks we hold and _after_
     * RecordTransactionCommit.
     */
    ProcArrayEndTransaction(MyProc, latestXid);

    /*
     * This is all post-commit cleanup.  Note that if an error is raised here,
     * it's too late to abort the transaction.  This should be just
     * noncritical resource releasing.
     *
     * The ordering of operations is not entirely random.  The idea is:
     * release resources visible to other backends (eg, files, buffer pins);
     * then release locks; then release backend-local resources. We want to
     * release locks at the point where any backend waiting for us will see
     * our transaction as being fully cleaned up.
     *
     * Resources that can be associated with individual queries are handled by
     * the ResourceOwner mechanism.  The other calls here are for backend-wide
     * state.
     */

    CallXactCallbacks(XACT_EVENT_COMMIT);

    ResourceOwnerRelease(TopTransactionResourceOwner,
                         RESOURCE_RELEASE_BEFORE_LOCKS,
                         true, true);

    /* Check we've released all buffer pins */
    AtEOXact_Buffers(true);

    /* Clean up the relation cache */
    AtEOXact_RelationCache(true);

    /*
     * Make catalog changes visible to all backends.  This has to happen after
     * relcache references are dropped (see comments for
     * AtEOXact_RelationCache), but before locks are released (if anyone is
     * waiting for lock on a relation we've modified, we want them to know
     * about the catalog change before they start using the relation).
     */
    AtEOXact_Inval(true);

    AtEOXact_MultiXact();

    ResourceOwnerRelease(TopTransactionResourceOwner,
                         RESOURCE_RELEASE_LOCKS,
                         true, true);
    ResourceOwnerRelease(TopTransactionResourceOwner,
                         RESOURCE_RELEASE_AFTER_LOCKS,
                         true, true);

    /*
     * Likewise, dropping of files deleted during the transaction is best done
     * after releasing relcache and buffer pins.  (This is not strictly
     * necessary during commit, since such pins should have been released
     * already, but this ordering is definitely critical during abort.)  Since
     * this may take many seconds, also delay until after releasing locks.
     * Other backends will observe the attendant catalog changes and not
     * attempt to access affected files.
     */
    smgrDoPendingDeletes(true);

    /* Check we've released all catcache entries */
    AtEOXact_CatCache(true);

    AtCommit_Notify();
    AtEOXact_GUC(true, 1);
    AtEOXact_SPI(true);
    AtEOXact_on_commit_actions(true);
    AtEOXact_Namespace(true);
    AtEOXact_SMgr();
    AtEOXact_Files();
    AtEOXact_ComboCid();
    AtEOXact_HashTables(true);
    AtEOXact_PgStat(true);
    AtEOXact_Snapshot(true);
    pgstat_report_xact_timestamp(0);

    CurrentResourceOwner = NULL;
    ResourceOwnerDelete(TopTransactionResourceOwner);
    s->curTransactionOwner = NULL;
    CurTransactionResourceOwner = NULL;
    TopTransactionResourceOwner = NULL;

    AtCommit_Memory();

    s->transactionId = InvalidTransactionId;
    s->subTransactionId = InvalidSubTransactionId;
    s->nestingLevel = 0;
    s->gucNestLevel = 0;
    s->childXids = NULL;
    s->nChildXids = 0;
    s->maxChildXids = 0;

    /*
     * done with commit processing, set current transaction state back to
     * default
     */
    s->state = TRANS_DEFAULT;

    RESUME_INTERRUPTS();
}


/*
 *  PrepareTransaction
 *
 * NB: if you change this routine, better look at CommitTransaction too!
 */
static void
PrepareTransaction(void)
{
    TransactionState s = CurrentTransactionState;
    TransactionId xid = GetCurrentTransactionId();
    GlobalTransaction gxact;
    TimestampTz prepared_at;

    ShowTransactionState("PrepareTransaction");

    /*
     * check the current transaction state
     */
    if (s->state != TRANS_INPROGRESS)
        elog(WARNING, "PrepareTransaction while in %s state",
             TransStateAsString(s->state));
    Assert(s->parent == NULL);

    /*
     * Do pre-commit processing that involves calling user-defined code, such
     * as triggers.  Since closing cursors could queue trigger actions,
     * triggers could open cursors, etc, we have to keep looping until there's
     * nothing left to do.
     */
    for (;;)
    {
        /*
         * Fire all currently pending deferred triggers.
         */
        AfterTriggerFireDeferred();

        /*
         * Close open portals (converting holdable ones into static portals).
         * If there weren't any, we are done ... otherwise loop back to check
         * if they queued deferred triggers.  Lather, rinse, repeat.
         */
        if (!PreCommit_Portals(true))
            break;
    }

    CallXactCallbacks(XACT_EVENT_PRE_PREPARE);

    /*
     * The remaining actions cannot call any user-defined code, so it's safe
     * to start shutting down within-transaction services.  But note that most
     * of this stuff could still throw an error, which would switch us into
     * the transaction-abort path.
     */

    /* Shut down the deferred-trigger manager */
    AfterTriggerEndXact(true);

    /*
     * Let ON COMMIT management do its thing (must happen after closing
     * cursors, to avoid dangling-reference problems)
     */
    PreCommit_on_commit_actions();

    /* close large objects before lower-level cleanup */
    AtEOXact_LargeObject(true);

    /*
     * Mark serializable transaction as complete for predicate locking
     * purposes.  This should be done as late as we can put it and still allow
     * errors to be raised for failure patterns found at commit.
     */
    PreCommit_CheckForSerializationFailure();

    /* NOTIFY will be handled below */

    /*
     * Don't allow PREPARE TRANSACTION if we've accessed a temporary table in
     * this transaction.  Having the prepared xact hold locks on another
     * backend's temp table seems a bad idea --- for instance it would prevent
     * the backend from exiting.  There are other problems too, such as how to
     * clean up the source backend's local buffers and ON COMMIT state if the
     * prepared xact includes a DROP of a temp table.
     *
     * We must check this after executing any ON COMMIT actions, because they
     * might still access a temp relation.
     *
     * XXX In principle this could be relaxed to allow some useful special
     * cases, such as a temp table created and dropped all within the
     * transaction.  That seems to require much more bookkeeping though.
     */
    if (MyXactAccessedTempRel)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("cannot PREPARE a transaction that has operated on temporary tables")));

    /*
     * Likewise, don't allow PREPARE after pg_export_snapshot.  This could be
     * supported if we added cleanup logic to twophase.c, but for now it
     * doesn't seem worth the trouble.
     */
    if (XactHasExportedSnapshots())
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
        errmsg("cannot PREPARE a transaction that has exported snapshots")));

    /* Prevent cancel/die interrupt while cleaning up */
    HOLD_INTERRUPTS();

    /*
     * set the current transaction state information appropriately during
     * prepare processing
     */
    s->state = TRANS_PREPARE;

    prepared_at = GetCurrentTimestamp();

    /* Tell bufmgr and smgr to prepare for commit */
    BufmgrCommit();

    /*
     * Reserve the GID for this transaction. This could fail if the requested
     * GID is invalid or already in use.
     */
    gxact = MarkAsPreparing(xid, prepareGID, prepared_at,
                            GetUserId(), MyDatabaseId);
    prepareGID = NULL;

    /*
     * Collect data for the 2PC state file.  Note that in general, no actual
     * state change should happen in the called modules during this step,
     * since it's still possible to fail before commit, and in that case we
     * want transaction abort to be able to clean up.  (In particular, the
     * AtPrepare routines may error out if they find cases they cannot
     * handle.)  State cleanup should happen in the PostPrepare routines
     * below.  However, some modules can go ahead and clear state here because
     * they wouldn't do anything with it during abort anyway.
     *
     * Note: because the 2PC state file records will be replayed in the same
     * order they are made, the order of these calls has to match the order in
     * which we want things to happen during COMMIT PREPARED or ROLLBACK
     * PREPARED; in particular, pay attention to whether things should happen
     * before or after releasing the transaction's locks.
     */
    StartPrepare(gxact);

    AtPrepare_Notify();
    AtPrepare_Locks();
    AtPrepare_PredicateLocks();
    AtPrepare_PgStat();
    AtPrepare_MultiXact();
    AtPrepare_RelationMap();

    /*
     * Here is where we really truly prepare.
     *
     * We have to record transaction prepares even if we didn't make any
     * updates, because the transaction manager might get confused if we lose
     * a global transaction.
     */
    EndPrepare(gxact);

    /*
     * Now we clean up backend-internal state and release internal resources.
     */

    /* Reset XactLastRecEnd until the next transaction writes something */
    XactLastRecEnd = 0;

    /*
     * Let others know about no transaction in progress by me.  This has to be
     * done *after* the prepared transaction has been marked valid, else
     * someone may think it is unlocked and recyclable.
     */
    ProcArrayClearTransaction(MyProc);

    /*
     * This is all post-transaction cleanup.  Note that if an error is raised
     * here, it's too late to abort the transaction.  This should be just
     * noncritical resource releasing.  See notes in CommitTransaction.
     */

    CallXactCallbacks(XACT_EVENT_PREPARE);

    ResourceOwnerRelease(TopTransactionResourceOwner,
                         RESOURCE_RELEASE_BEFORE_LOCKS,
                         true, true);

    /* Check we've released all buffer pins */
    AtEOXact_Buffers(true);

    /* Clean up the relation cache */
    AtEOXact_RelationCache(true);

    /* notify doesn't need a postprepare call */

    PostPrepare_PgStat();

    PostPrepare_Inval();

    PostPrepare_smgr();

    PostPrepare_MultiXact(xid);

    PostPrepare_Locks(xid);
    PostPrepare_PredicateLocks(xid);

    ResourceOwnerRelease(TopTransactionResourceOwner,
                         RESOURCE_RELEASE_LOCKS,
                         true, true);
    ResourceOwnerRelease(TopTransactionResourceOwner,
                         RESOURCE_RELEASE_AFTER_LOCKS,
                         true, true);

    /* Check we've released all catcache entries */
    AtEOXact_CatCache(true);

    /* PREPARE acts the same as COMMIT as far as GUC is concerned */
    AtEOXact_GUC(true, 1);
    AtEOXact_SPI(true);
    AtEOXact_on_commit_actions(true);
    AtEOXact_Namespace(true);
    AtEOXact_SMgr();
    AtEOXact_Files();
    AtEOXact_ComboCid();
    AtEOXact_HashTables(true);
    /* don't call AtEOXact_PgStat here */
    AtEOXact_Snapshot(true);

    CurrentResourceOwner = NULL;
    ResourceOwnerDelete(TopTransactionResourceOwner);
    s->curTransactionOwner = NULL;
    CurTransactionResourceOwner = NULL;
    TopTransactionResourceOwner = NULL;

    AtCommit_Memory();

    s->transactionId = InvalidTransactionId;
    s->subTransactionId = InvalidSubTransactionId;
    s->nestingLevel = 0;
    s->gucNestLevel = 0;
    s->childXids = NULL;
    s->nChildXids = 0;
    s->maxChildXids = 0;

    /*
     * done with 1st phase commit processing, set current transaction state
     * back to default
     */
    s->state = TRANS_DEFAULT;

    RESUME_INTERRUPTS();
}


/*
 *  AbortTransaction
 */
static void
AbortTransaction(void)
{
    TransactionState s = CurrentTransactionState;
    TransactionId latestXid;

    /* Prevent cancel/die interrupt while cleaning up */
    HOLD_INTERRUPTS();

    /* Make sure we have a valid memory context and resource owner */
    AtAbort_Memory();
    AtAbort_ResourceOwner();

    /*
     * Release any LW locks we might be holding as quickly as possible.
     * (Regular locks, however, must be held till we finish aborting.)
     * Releasing LW locks is critical since we might try to grab them again
     * while cleaning up!
     */
    LWLockReleaseAll();

    /* Clean up buffer I/O and buffer context locks, too */
    AbortBufferIO();
    UnlockBuffers();

    /*
     * Also clean up any open wait for lock, since the lock manager will choke
     * if we try to wait for another lock before doing this.
     */
    LockErrorCleanup();

    /*
     * check the current transaction state
     */
    if (s->state != TRANS_INPROGRESS && s->state != TRANS_PREPARE)
        elog(WARNING, "AbortTransaction while in %s state",
             TransStateAsString(s->state));
    Assert(s->parent == NULL);

    /*
     * set the current transaction state information appropriately during the
     * abort processing
     */
    s->state = TRANS_ABORT;

    /*
     * Reset user ID which might have been changed transiently.  We need this
     * to clean up in case control escaped out of a SECURITY DEFINER function
     * or other local change of CurrentUserId; therefore, the prior value of
     * SecurityRestrictionContext also needs to be restored.
     *
     * (Note: it is not necessary to restore session authorization or role
     * settings here because those can only be changed via GUC, and GUC will
     * take care of rolling them back if need be.)
     */
    SetUserIdAndSecContext(s->prevUser, s->prevSecContext);

    /*
     * do abort processing
     */
    AfterTriggerEndXact(false); /* 'false' means it's abort */
    AtAbort_Portals();
    AtEOXact_LargeObject(false);
    AtAbort_Notify();
    AtEOXact_RelationMap(false);

    /*
     * Advertise the fact that we aborted in pg_clog (assuming that we got as
     * far as assigning an XID to advertise).
     */
    latestXid = RecordTransactionAbort(false);

    TRACE_POSTGRESQL_TRANSACTION_ABORT(MyProc->lxid);

    /*
     * Let others know about no transaction in progress by me. Note that this
     * must be done _before_ releasing locks we hold and _after_
     * RecordTransactionAbort.
     */
    ProcArrayEndTransaction(MyProc, latestXid);

    /*
     * Post-abort cleanup.  See notes in CommitTransaction() concerning
     * ordering.  We can skip all of it if the transaction failed before
     * creating a resource owner.
     */
    if (TopTransactionResourceOwner != NULL)
    {
        CallXactCallbacks(XACT_EVENT_ABORT);

        ResourceOwnerRelease(TopTransactionResourceOwner,
                             RESOURCE_RELEASE_BEFORE_LOCKS,
                             false, true);
        AtEOXact_Buffers(false);
        AtEOXact_RelationCache(false);
        AtEOXact_Inval(false);
        AtEOXact_MultiXact();
        ResourceOwnerRelease(TopTransactionResourceOwner,
                             RESOURCE_RELEASE_LOCKS,
                             false, true);
        ResourceOwnerRelease(TopTransactionResourceOwner,
                             RESOURCE_RELEASE_AFTER_LOCKS,
                             false, true);
        smgrDoPendingDeletes(false);
        AtEOXact_CatCache(false);

        AtEOXact_GUC(false, 1);
        AtEOXact_SPI(false);
        AtEOXact_on_commit_actions(false);
        AtEOXact_Namespace(false);
        AtEOXact_SMgr();
        AtEOXact_Files();
        AtEOXact_ComboCid();
        AtEOXact_HashTables(false);
        AtEOXact_PgStat(false);
        pgstat_report_xact_timestamp(0);
    }

    /*
     * State remains TRANS_ABORT until CleanupTransaction().
     */
    RESUME_INTERRUPTS();
}

/*
 *  CleanupTransaction
 */
static void
CleanupTransaction(void)
{
    TransactionState s = CurrentTransactionState;

    /*
     * State should still be TRANS_ABORT from AbortTransaction().
     */
    if (s->state != TRANS_ABORT)
        elog(FATAL, "CleanupTransaction: unexpected state %s",
             TransStateAsString(s->state));

    /*
     * do abort cleanup processing
     */
    AtCleanup_Portals();        /* now safe to release portal memory */
    AtEOXact_Snapshot(false);   /* and release the transaction's snapshots */

    CurrentResourceOwner = NULL;    /* and resource owner */
    if (TopTransactionResourceOwner)
        ResourceOwnerDelete(TopTransactionResourceOwner);
    s->curTransactionOwner = NULL;
    CurTransactionResourceOwner = NULL;
    TopTransactionResourceOwner = NULL;

    AtCleanup_Memory();         /* and transaction memory */

    s->transactionId = InvalidTransactionId;
    s->subTransactionId = InvalidSubTransactionId;
    s->nestingLevel = 0;
    s->gucNestLevel = 0;
    s->childXids = NULL;
    s->nChildXids = 0;
    s->maxChildXids = 0;

    /*
     * done with abort processing, set current transaction state back to
     * default
     */
    s->state = TRANS_DEFAULT;
}

/*
 *  StartTransactionCommand
 */
void
StartTransactionCommand(void)
{
    TransactionState s = CurrentTransactionState;

    switch (s->blockState)
    {
            /*
             * if we aren't in a transaction block, we just do our usual start
             * transaction.
             */
        case TBLOCK_DEFAULT:
            StartTransaction();
            s->blockState = TBLOCK_STARTED;
            break;

            /*
             * We are somewhere in a transaction block or subtransaction and
             * about to start a new command.  For now we do nothing, but
             * someday we may do command-local resource initialization. (Note
             * that any needed CommandCounterIncrement was done by the
             * previous CommitTransactionCommand.)
             */
        case TBLOCK_INPROGRESS:
        case TBLOCK_SUBINPROGRESS:
            break;

            /*
             * Here we are in a failed transaction block (one of the commands
             * caused an abort) so we do nothing but remain in the abort
             * state.  Eventually we will get a ROLLBACK command which will
             * get us out of this state.  (It is up to other code to ensure
             * that no commands other than ROLLBACK will be processed in these
             * states.)
             */
        case TBLOCK_ABORT:
        case TBLOCK_SUBABORT:
            break;

            /* These cases are invalid. */
        case TBLOCK_STARTED:
        case TBLOCK_BEGIN:
        case TBLOCK_SUBBEGIN:
        case TBLOCK_END:
        case TBLOCK_SUBRELEASE:
        case TBLOCK_SUBCOMMIT:
        case TBLOCK_ABORT_END:
        case TBLOCK_SUBABORT_END:
        case TBLOCK_ABORT_PENDING:
        case TBLOCK_SUBABORT_PENDING:
        case TBLOCK_SUBRESTART:
        case TBLOCK_SUBABORT_RESTART:
        case TBLOCK_PREPARE:
            elog(ERROR, "StartTransactionCommand: unexpected state %s",
                 BlockStateAsString(s->blockState));
            break;
    }

    /*
     * We must switch to CurTransactionContext before returning. This is
     * already done if we called StartTransaction, otherwise not.
     */
    Assert(CurTransactionContext != NULL);
    MemoryContextSwitchTo(CurTransactionContext);
}

/*
 *  CommitTransactionCommand
 */
void
CommitTransactionCommand(void)
{
    TransactionState s = CurrentTransactionState;

    switch (s->blockState)
    {
            /*
             * This shouldn't happen, because it means the previous
             * StartTransactionCommand didn't set the STARTED state
             * appropriately.
             */
        case TBLOCK_DEFAULT:
            elog(FATAL, "CommitTransactionCommand: unexpected state %s",
                 BlockStateAsString(s->blockState));
            break;

            /*
             * If we aren't in a transaction block, just do our usual
             * transaction commit, and return to the idle state.
             */
        case TBLOCK_STARTED:
            CommitTransaction();
            s->blockState = TBLOCK_DEFAULT;
            break;

            /*
             * We are completing a "BEGIN TRANSACTION" command, so we change
             * to the "transaction block in progress" state and return.  (We
             * assume the BEGIN did nothing to the database, so we need no
             * CommandCounterIncrement.)
             */
        case TBLOCK_BEGIN:
            s->blockState = TBLOCK_INPROGRESS;
            break;

            /*
             * This is the case when we have finished executing a command
             * someplace within a transaction block.  We increment the command
             * counter and return.
             */
        case TBLOCK_INPROGRESS:
        case TBLOCK_SUBINPROGRESS:
            CommandCounterIncrement();
            break;

            /*
             * We are completing a "COMMIT" command.  Do it and return to the
             * idle state.
             */
        case TBLOCK_END:
            CommitTransaction();
            s->blockState = TBLOCK_DEFAULT;
            break;

            /*
             * Here we are in the middle of a transaction block but one of the
             * commands caused an abort so we do nothing but remain in the
             * abort state.  Eventually we will get a ROLLBACK comand.
             */
        case TBLOCK_ABORT:
        case TBLOCK_SUBABORT:
            break;

            /*
             * Here we were in an aborted transaction block and we just got
             * the ROLLBACK command from the user, so clean up the
             * already-aborted transaction and return to the idle state.
             */
        case TBLOCK_ABORT_END:
            CleanupTransaction();
            s->blockState = TBLOCK_DEFAULT;
            break;

            /*
             * Here we were in a perfectly good transaction block but the user
             * told us to ROLLBACK anyway.  We have to abort the transaction
             * and then clean up.
             */
        case TBLOCK_ABORT_PENDING:
            AbortTransaction();
            CleanupTransaction();
            s->blockState = TBLOCK_DEFAULT;
            break;

            /*
             * We are completing a "PREPARE TRANSACTION" command.  Do it and
             * return to the idle state.
             */
        case TBLOCK_PREPARE:
            PrepareTransaction();
            s->blockState = TBLOCK_DEFAULT;
            break;

            /*
             * We were just issued a SAVEPOINT inside a transaction block.
             * Start a subtransaction.  (DefineSavepoint already did
             * PushTransaction, so as to have someplace to put the SUBBEGIN
             * state.)
             */
        case TBLOCK_SUBBEGIN:
            StartSubTransaction();
            s->blockState = TBLOCK_SUBINPROGRESS;
            break;

            /*
             * We were issued a RELEASE command, so we end the current
             * subtransaction and return to the parent transaction. The parent
             * might be ended too, so repeat till we find an INPROGRESS
             * transaction or subtransaction.
             */
        case TBLOCK_SUBRELEASE:
            do
            {
                CommitSubTransaction();
                s = CurrentTransactionState;    /* changed by pop */
            } while (s->blockState == TBLOCK_SUBRELEASE);

            Assert(s->blockState == TBLOCK_INPROGRESS ||
                   s->blockState == TBLOCK_SUBINPROGRESS);
            break;

            /*
             * We were issued a COMMIT, so we end the current subtransaction
             * hierarchy and perform final commit. We do this by rolling up
             * any subtransactions into their parent, which leads to O(N^2)
             * operations with respect to resource owners - this isn't that
             * bad until we approach a thousands of savepoints but is
             * necessary for correctness should after triggers create new
             * resource owners.
             */
        case TBLOCK_SUBCOMMIT:
            do
            {
                CommitSubTransaction();
                s = CurrentTransactionState;    /* changed by pop */
            } while (s->blockState == TBLOCK_SUBCOMMIT);
            /* If we had a COMMIT command, finish off the main xact too */
            if (s->blockState == TBLOCK_END)
            {
                Assert(s->parent == NULL);
                CommitTransaction();
                s->blockState = TBLOCK_DEFAULT;
            }
            else if (s->blockState == TBLOCK_PREPARE)
            {
                Assert(s->parent == NULL);
                PrepareTransaction();
                s->blockState = TBLOCK_DEFAULT;
            }
            else
                elog(ERROR, "CommitTransactionCommand: unexpected state %s",
                     BlockStateAsString(s->blockState));
            break;

            /*
             * The current already-failed subtransaction is ending due to a
             * ROLLBACK or ROLLBACK TO command, so pop it and recursively
             * examine the parent (which could be in any of several states).
             */
        case TBLOCK_SUBABORT_END:
            CleanupSubTransaction();
            CommitTransactionCommand();
            break;

            /*
             * As above, but it's not dead yet, so abort first.
             */
        case TBLOCK_SUBABORT_PENDING:
            AbortSubTransaction();
            CleanupSubTransaction();
            CommitTransactionCommand();
            break;

            /*
             * The current subtransaction is the target of a ROLLBACK TO
             * command.  Abort and pop it, then start a new subtransaction
             * with the same name.
             */
        case TBLOCK_SUBRESTART:
            {
                char       *name;
                int         savepointLevel;

                /* save name and keep Cleanup from freeing it */
                name = s->name;
                s->name = NULL;
                savepointLevel = s->savepointLevel;

                AbortSubTransaction();
                CleanupSubTransaction();

                DefineSavepoint(NULL);
                s = CurrentTransactionState;    /* changed by push */
                s->name = name;
                s->savepointLevel = savepointLevel;

                /* This is the same as TBLOCK_SUBBEGIN case */
                AssertState(s->blockState == TBLOCK_SUBBEGIN);
                StartSubTransaction();
                s->blockState = TBLOCK_SUBINPROGRESS;
            }
            break;

            /*
             * Same as above, but the subtransaction had already failed, so we
             * don't need AbortSubTransaction.
             */
        case TBLOCK_SUBABORT_RESTART:
            {
                char       *name;
                int         savepointLevel;

                /* save name and keep Cleanup from freeing it */
                name = s->name;
                s->name = NULL;
                savepointLevel = s->savepointLevel;

                CleanupSubTransaction();

                DefineSavepoint(NULL);
                s = CurrentTransactionState;    /* changed by push */
                s->name = name;
                s->savepointLevel = savepointLevel;

                /* This is the same as TBLOCK_SUBBEGIN case */
                AssertState(s->blockState == TBLOCK_SUBBEGIN);
                StartSubTransaction();
                s->blockState = TBLOCK_SUBINPROGRESS;
            }
            break;
    }
}

/*
 *  AbortCurrentTransaction
 */
void
AbortCurrentTransaction(void)
{
    TransactionState s = CurrentTransactionState;

    switch (s->blockState)
    {
        case TBLOCK_DEFAULT:
            if (s->state == TRANS_DEFAULT)
            {
                /* we are idle, so nothing to do */
            }
            else
            {
                /*
                 * We can get here after an error during transaction start
                 * (state will be TRANS_START).  Need to clean up the
                 * incompletely started transaction.  First, adjust the
                 * low-level state to suppress warning message from
                 * AbortTransaction.
                 */
                if (s->state == TRANS_START)
                    s->state = TRANS_INPROGRESS;
                AbortTransaction();
                CleanupTransaction();
            }
            break;

            /*
             * if we aren't in a transaction block, we just do the basic abort
             * & cleanup transaction.
             */
        case TBLOCK_STARTED:
            AbortTransaction();
            CleanupTransaction();
            s->blockState = TBLOCK_DEFAULT;
            break;

            /*
             * If we are in TBLOCK_BEGIN it means something screwed up right
             * after reading "BEGIN TRANSACTION".  We assume that the user
             * will interpret the error as meaning the BEGIN failed to get him
             * into a transaction block, so we should abort and return to idle
             * state.
             */
        case TBLOCK_BEGIN:
            AbortTransaction();
            CleanupTransaction();
            s->blockState = TBLOCK_DEFAULT;
            break;

            /*
             * We are somewhere in a transaction block and we've gotten a
             * failure, so we abort the transaction and set up the persistent
             * ABORT state.  We will stay in ABORT until we get a ROLLBACK.
             */
        case TBLOCK_INPROGRESS:
            AbortTransaction();
            s->blockState = TBLOCK_ABORT;
            /* CleanupTransaction happens when we exit TBLOCK_ABORT_END */
            break;

            /*
             * Here, we failed while trying to COMMIT.  Clean up the
             * transaction and return to idle state (we do not want to stay in
             * the transaction).
             */
        case TBLOCK_END:
            AbortTransaction();
            CleanupTransaction();
            s->blockState = TBLOCK_DEFAULT;
            break;

            /*
             * Here, we are already in an aborted transaction state and are
             * waiting for a ROLLBACK, but for some reason we failed again! So
             * we just remain in the abort state.
             */
        case TBLOCK_ABORT:
        case TBLOCK_SUBABORT:
            break;

            /*
             * We are in a failed transaction and we got the ROLLBACK command.
             * We have already aborted, we just need to cleanup and go to idle
             * state.
             */
        case TBLOCK_ABORT_END:
            CleanupTransaction();
            s->blockState = TBLOCK_DEFAULT;
            break;

            /*
             * We are in a live transaction and we got a ROLLBACK command.
             * Abort, cleanup, go to idle state.
             */
        case TBLOCK_ABORT_PENDING:
            AbortTransaction();
            CleanupTransaction();
            s->blockState = TBLOCK_DEFAULT;
            break;

            /*
             * Here, we failed while trying to PREPARE.  Clean up the
             * transaction and return to idle state (we do not want to stay in
             * the transaction).
             */
        case TBLOCK_PREPARE:
            AbortTransaction();
            CleanupTransaction();
            s->blockState = TBLOCK_DEFAULT;
            break;

            /*
             * We got an error inside a subtransaction.  Abort just the
             * subtransaction, and go to the persistent SUBABORT state until
             * we get ROLLBACK.
             */
        case TBLOCK_SUBINPROGRESS:
            AbortSubTransaction();
            s->blockState = TBLOCK_SUBABORT;
            break;

            /*
             * If we failed while trying to create a subtransaction, clean up
             * the broken subtransaction and abort the parent.  The same
             * applies if we get a failure while ending a subtransaction.
             */
        case TBLOCK_SUBBEGIN:
        case TBLOCK_SUBRELEASE:
        case TBLOCK_SUBCOMMIT:
        case TBLOCK_SUBABORT_PENDING:
        case TBLOCK_SUBRESTART:
            AbortSubTransaction();
            CleanupSubTransaction();
            AbortCurrentTransaction();
            break;

            /*
             * Same as above, except the Abort() was already done.
             */
        case TBLOCK_SUBABORT_END:
        case TBLOCK_SUBABORT_RESTART:
            CleanupSubTransaction();
            AbortCurrentTransaction();
            break;
    }
}

/*
 *  PreventTransactionChain
 *
 *  This routine is to be called by statements that must not run inside
 *  a transaction block, typically because they have non-rollback-able
 *  side effects or do internal commits.
 *
 *  If we have already started a transaction block, issue an error; also issue
 *  an error if we appear to be running inside a user-defined function (which
 *  could issue more commands and possibly cause a failure after the statement
 *  completes).  Subtransactions are verboten too.
 *
 *  isTopLevel: passed down from ProcessUtility to determine whether we are
 *  inside a function or multi-query querystring.  (We will always fail if
 *  this is false, but it's convenient to centralize the check here instead of
 *  making callers do it.)
 *  stmtType: statement type name, for error messages.
 */
void
PreventTransactionChain(bool isTopLevel, const char *stmtType)
{
    /*
     * xact block already started?
     */
    if (IsTransactionBlock())
        ereport(ERROR,
                (errcode(ERRCODE_ACTIVE_SQL_TRANSACTION),
        /* translator: %s represents an SQL statement name */
                 errmsg("%s cannot run inside a transaction block",
                        stmtType)));

    /*
     * subtransaction?
     */
    if (IsSubTransaction())
        ereport(ERROR,
                (errcode(ERRCODE_ACTIVE_SQL_TRANSACTION),
        /* translator: %s represents an SQL statement name */
                 errmsg("%s cannot run inside a subtransaction",
                        stmtType)));

    /*
     * inside a function call?
     */
    if (!isTopLevel)
        ereport(ERROR,
                (errcode(ERRCODE_ACTIVE_SQL_TRANSACTION),
        /* translator: %s represents an SQL statement name */
                 errmsg("%s cannot be executed from a function or multi-command string",
                        stmtType)));

    /* If we got past IsTransactionBlock test, should be in default state */
    if (CurrentTransactionState->blockState != TBLOCK_DEFAULT &&
        CurrentTransactionState->blockState != TBLOCK_STARTED)
        elog(FATAL, "cannot prevent transaction chain");
    /* all okay */
}

/*
 *  RequireTransactionChain
 *
 *  This routine is to be called by statements that must run inside
 *  a transaction block, because they have no effects that persist past
 *  transaction end (and so calling them outside a transaction block
 *  is presumably an error).  DECLARE CURSOR is an example.
 *
 *  If we appear to be running inside a user-defined function, we do not
 *  issue an error, since the function could issue more commands that make
 *  use of the current statement's results.  Likewise subtransactions.
 *  Thus this is an inverse for PreventTransactionChain.
 *
 *  isTopLevel: passed down from ProcessUtility to determine whether we are
 *  inside a function.
 *  stmtType: statement type name, for error messages.
 */
void
RequireTransactionChain(bool isTopLevel, const char *stmtType)
{
    /*
     * xact block already started?
     */
    if (IsTransactionBlock())
        return;

    /*
     * subtransaction?
     */
    if (IsSubTransaction())
        return;

    /*
     * inside a function call?
     */
    if (!isTopLevel)
        return;

    ereport(ERROR,
            (errcode(ERRCODE_NO_ACTIVE_SQL_TRANSACTION),
    /* translator: %s represents an SQL statement name */
             errmsg("%s can only be used in transaction blocks",
                    stmtType)));
}

/*
 *  IsInTransactionChain
 *
 *  This routine is for statements that need to behave differently inside
 *  a transaction block than when running as single commands.  ANALYZE is
 *  currently the only example.
 *
 *  isTopLevel: passed down from ProcessUtility to determine whether we are
 *  inside a function.
 */
bool
IsInTransactionChain(bool isTopLevel)
{
    /*
     * Return true on same conditions that would make PreventTransactionChain
     * error out
     */
    if (IsTransactionBlock())
        return true;

    if (IsSubTransaction())
        return true;

    if (!isTopLevel)
        return true;

    if (CurrentTransactionState->blockState != TBLOCK_DEFAULT &&
        CurrentTransactionState->blockState != TBLOCK_STARTED)
        return true;

    return false;
}


/*
 * Register or deregister callback functions for start- and end-of-xact
 * operations.
 *
 * These functions are intended for use by dynamically loaded modules.
 * For built-in modules we generally just hardwire the appropriate calls
 * (mainly because it's easier to control the order that way, where needed).
 *
 * At transaction end, the callback occurs post-commit or post-abort, so the
 * callback functions can only do noncritical cleanup.
 */
void
RegisterXactCallback(XactCallback callback, void *arg)
{
    XactCallbackItem *item;

    item = (XactCallbackItem *)
        MemoryContextAlloc(TopMemoryContext, sizeof(XactCallbackItem));
    item->callback = callback;
    item->arg = arg;
    item->next = Xact_callbacks;
    Xact_callbacks = item;
}

void
UnregisterXactCallback(XactCallback callback, void *arg)
{
    XactCallbackItem *item;
    XactCallbackItem *prev;

    prev = NULL;
    for (item = Xact_callbacks; item; prev = item, item = item->next)
    {
        if (item->callback == callback && item->arg == arg)
        {
            if (prev)
                prev->next = item->next;
            else
                Xact_callbacks = item->next;
            pfree(item);
            break;
        }
    }
}

static void
CallXactCallbacks(XactEvent event)
{
    XactCallbackItem *item;

    for (item = Xact_callbacks; item; item = item->next)
        (*item->callback) (event, item->arg);
}


/*
 * Register or deregister callback functions for start- and end-of-subxact
 * operations.
 *
 * Pretty much same as above, but for subtransaction events.
 *
 * At subtransaction end, the callback occurs post-subcommit or post-subabort,
 * so the callback functions can only do noncritical cleanup.  At
 * subtransaction start, the callback is called when the subtransaction has
 * finished initializing.
 */
void
RegisterSubXactCallback(SubXactCallback callback, void *arg)
{
    SubXactCallbackItem *item;

    item = (SubXactCallbackItem *)
        MemoryContextAlloc(TopMemoryContext, sizeof(SubXactCallbackItem));
    item->callback = callback;
    item->arg = arg;
    item->next = SubXact_callbacks;
    SubXact_callbacks = item;
}

void
UnregisterSubXactCallback(SubXactCallback callback, void *arg)
{
    SubXactCallbackItem *item;
    SubXactCallbackItem *prev;

    prev = NULL;
    for (item = SubXact_callbacks; item; prev = item, item = item->next)
    {
        if (item->callback == callback && item->arg == arg)
        {
            if (prev)
                prev->next = item->next;
            else
                SubXact_callbacks = item->next;
            pfree(item);
            break;
        }
    }
}

static void
CallSubXactCallbacks(SubXactEvent event,
                     SubTransactionId mySubid,
                     SubTransactionId parentSubid)
{
    SubXactCallbackItem *item;

    for (item = SubXact_callbacks; item; item = item->next)
        (*item->callback) (event, mySubid, parentSubid, item->arg);
}


/* ----------------------------------------------------------------
 *                     transaction block support
 * ----------------------------------------------------------------
 */

/*
 *  BeginTransactionBlock
 *      This executes a BEGIN command.
 */
void
BeginTransactionBlock(void)
{
    TransactionState s = CurrentTransactionState;

    switch (s->blockState)
    {
            /*
             * We are not inside a transaction block, so allow one to begin.
             */
        case TBLOCK_STARTED:
            s->blockState = TBLOCK_BEGIN;
            break;

            /*
             * Already a transaction block in progress.
             */
        case TBLOCK_INPROGRESS:
        case TBLOCK_SUBINPROGRESS:
        case TBLOCK_ABORT:
        case TBLOCK_SUBABORT:
            ereport(WARNING,
                    (errcode(ERRCODE_ACTIVE_SQL_TRANSACTION),
                     errmsg("there is already a transaction in progress")));
            break;

            /* These cases are invalid. */
        case TBLOCK_DEFAULT:
        case TBLOCK_BEGIN:
        case TBLOCK_SUBBEGIN:
        case TBLOCK_END:
        case TBLOCK_SUBRELEASE:
        case TBLOCK_SUBCOMMIT:
        case TBLOCK_ABORT_END:
        case TBLOCK_SUBABORT_END:
        case TBLOCK_ABORT_PENDING:
        case TBLOCK_SUBABORT_PENDING:
        case TBLOCK_SUBRESTART:
        case TBLOCK_SUBABORT_RESTART:
        case TBLOCK_PREPARE:
            elog(FATAL, "BeginTransactionBlock: unexpected state %s",
                 BlockStateAsString(s->blockState));
            break;
    }
}

/*
 *  PrepareTransactionBlock
 *      This executes a PREPARE command.
 *
 * Since PREPARE may actually do a ROLLBACK, the result indicates what
 * happened: TRUE for PREPARE, FALSE for ROLLBACK.
 *
 * Note that we don't actually do anything here except change blockState.
 * The real work will be done in the upcoming PrepareTransaction().
 * We do it this way because it's not convenient to change memory context,
 * resource owner, etc while executing inside a Portal.
 */
bool
PrepareTransactionBlock(char *gid)
{
    TransactionState s;
    bool        result;

    /* Set up to commit the current transaction */
    result = EndTransactionBlock();

    /* If successful, change outer tblock state to PREPARE */
    if (result)
    {
        s = CurrentTransactionState;

        while (s->parent != NULL)
            s = s->parent;

        if (s->blockState == TBLOCK_END)
        {
            /* Save GID where PrepareTransaction can find it again */
            prepareGID = MemoryContextStrdup(TopTransactionContext, gid);

            s->blockState = TBLOCK_PREPARE;
        }
        else
        {
            /*
             * ignore case where we are not in a transaction;
             * EndTransactionBlock already issued a warning.
             */
            Assert(s->blockState == TBLOCK_STARTED);
            /* Don't send back a PREPARE result tag... */
            result = false;
        }
    }

    return result;
}

/*
 *  EndTransactionBlock
 *      This executes a COMMIT command.
 *
 * Since COMMIT may actually do a ROLLBACK, the result indicates what
 * happened: TRUE for COMMIT, FALSE for ROLLBACK.
 *
 * Note that we don't actually do anything here except change blockState.
 * The real work will be done in the upcoming CommitTransactionCommand().
 * We do it this way because it's not convenient to change memory context,
 * resource owner, etc while executing inside a Portal.
 */
bool
EndTransactionBlock(void)
{
    TransactionState s = CurrentTransactionState;
    bool        result = false;

    switch (s->blockState)
    {
            /*
             * We are in a transaction block, so tell CommitTransactionCommand
             * to COMMIT.
             */
        case TBLOCK_INPROGRESS:
            s->blockState = TBLOCK_END;
            result = true;
            break;

            /*
             * We are in a failed transaction block.  Tell
             * CommitTransactionCommand it's time to exit the block.
             */
        case TBLOCK_ABORT:
            s->blockState = TBLOCK_ABORT_END;
            break;

            /*
             * We are in a live subtransaction block.  Set up to subcommit all
             * open subtransactions and then commit the main transaction.
             */
        case TBLOCK_SUBINPROGRESS:
            while (s->parent != NULL)
            {
                if (s->blockState == TBLOCK_SUBINPROGRESS)
                    s->blockState = TBLOCK_SUBCOMMIT;
                else
                    elog(FATAL, "EndTransactionBlock: unexpected state %s",
                         BlockStateAsString(s->blockState));
                s = s->parent;
            }
            if (s->blockState == TBLOCK_INPROGRESS)
                s->blockState = TBLOCK_END;
            else
                elog(FATAL, "EndTransactionBlock: unexpected state %s",
                     BlockStateAsString(s->blockState));
            result = true;
            break;

            /*
             * Here we are inside an aborted subtransaction.  Treat the COMMIT
             * as ROLLBACK: set up to abort everything and exit the main
             * transaction.
             */
        case TBLOCK_SUBABORT:
            while (s->parent != NULL)
            {
                if (s->blockState == TBLOCK_SUBINPROGRESS)
                    s->blockState = TBLOCK_SUBABORT_PENDING;
                else if (s->blockState == TBLOCK_SUBABORT)
                    s->blockState = TBLOCK_SUBABORT_END;
                else
                    elog(FATAL, "EndTransactionBlock: unexpected state %s",
                         BlockStateAsString(s->blockState));
                s = s->parent;
            }
            if (s->blockState == TBLOCK_INPROGRESS)
                s->blockState = TBLOCK_ABORT_PENDING;
            else if (s->blockState == TBLOCK_ABORT)
                s->blockState = TBLOCK_ABORT_END;
            else
                elog(FATAL, "EndTransactionBlock: unexpected state %s",
                     BlockStateAsString(s->blockState));
            break;

            /*
             * The user issued COMMIT when not inside a transaction.  Issue a
             * WARNING, staying in TBLOCK_STARTED state.  The upcoming call to
             * CommitTransactionCommand() will then close the transaction and
             * put us back into the default state.
             */
        case TBLOCK_STARTED:
            ereport(WARNING,
                    (errcode(ERRCODE_NO_ACTIVE_SQL_TRANSACTION),
                     errmsg("there is no transaction in progress")));
            result = true;
            break;

            /* These cases are invalid. */
        case TBLOCK_DEFAULT:
        case TBLOCK_BEGIN:
        case TBLOCK_SUBBEGIN:
        case TBLOCK_END:
        case TBLOCK_SUBRELEASE:
        case TBLOCK_SUBCOMMIT:
        case TBLOCK_ABORT_END:
        case TBLOCK_SUBABORT_END:
        case TBLOCK_ABORT_PENDING:
        case TBLOCK_SUBABORT_PENDING:
        case TBLOCK_SUBRESTART:
        case TBLOCK_SUBABORT_RESTART:
        case TBLOCK_PREPARE:
            elog(FATAL, "EndTransactionBlock: unexpected state %s",
                 BlockStateAsString(s->blockState));
            break;
    }

    return result;
}

/*
 *  UserAbortTransactionBlock
 *      This executes a ROLLBACK command.
 *
 * As above, we don't actually do anything here except change blockState.
 */
void
UserAbortTransactionBlock(void)
{
    TransactionState s = CurrentTransactionState;

    switch (s->blockState)
    {
            /*
             * We are inside a transaction block and we got a ROLLBACK command
             * from the user, so tell CommitTransactionCommand to abort and
             * exit the transaction block.
             */
        case TBLOCK_INPROGRESS:
            s->blockState = TBLOCK_ABORT_PENDING;
            break;

            /*
             * We are inside a failed transaction block and we got a ROLLBACK
             * command from the user.  Abort processing is already done, so
             * CommitTransactionCommand just has to cleanup and go back to
             * idle state.
             */
        case TBLOCK_ABORT:
            s->blockState = TBLOCK_ABORT_END;
            break;

            /*
             * We are inside a subtransaction.  Mark everything up to top
             * level as exitable.
             */
        case TBLOCK_SUBINPROGRESS:
        case TBLOCK_SUBABORT:
            while (s->parent != NULL)
            {
                if (s->blockState == TBLOCK_SUBINPROGRESS)
                    s->blockState = TBLOCK_SUBABORT_PENDING;
                else if (s->blockState == TBLOCK_SUBABORT)
                    s->blockState = TBLOCK_SUBABORT_END;
                else
                    elog(FATAL, "UserAbortTransactionBlock: unexpected state %s",
                         BlockStateAsString(s->blockState));
                s = s->parent;
            }
            if (s->blockState == TBLOCK_INPROGRESS)
                s->blockState = TBLOCK_ABORT_PENDING;
            else if (s->blockState == TBLOCK_ABORT)
                s->blockState = TBLOCK_ABORT_END;
            else
                elog(FATAL, "UserAbortTransactionBlock: unexpected state %s",
                     BlockStateAsString(s->blockState));
            break;

            /*
             * The user issued ABORT when not inside a transaction. Issue a
             * NOTICE and go to abort state.  The upcoming call to
             * CommitTransactionCommand() will then put us back into the
             * default state.
             */
        case TBLOCK_STARTED:
            ereport(NOTICE,
                    (errcode(ERRCODE_NO_ACTIVE_SQL_TRANSACTION),
                     errmsg("there is no transaction in progress")));
            s->blockState = TBLOCK_ABORT_PENDING;
            break;

            /* These cases are invalid. */
        case TBLOCK_DEFAULT:
        case TBLOCK_BEGIN:
        case TBLOCK_SUBBEGIN:
        case TBLOCK_END:
        case TBLOCK_SUBRELEASE:
        case TBLOCK_SUBCOMMIT:
        case TBLOCK_ABORT_END:
        case TBLOCK_SUBABORT_END:
        case TBLOCK_ABORT_PENDING:
        case TBLOCK_SUBABORT_PENDING:
        case TBLOCK_SUBRESTART:
        case TBLOCK_SUBABORT_RESTART:
        case TBLOCK_PREPARE:
            elog(FATAL, "UserAbortTransactionBlock: unexpected state %s",
                 BlockStateAsString(s->blockState));
            break;
    }
}

/*
 * DefineSavepoint
 *      This executes a SAVEPOINT command.
 */
void
DefineSavepoint(char *name)
{
    TransactionState s = CurrentTransactionState;

    switch (s->blockState)
    {
        case TBLOCK_INPROGRESS:
        case TBLOCK_SUBINPROGRESS:
            /* Normal subtransaction start */
            PushTransaction();
            s = CurrentTransactionState;        /* changed by push */

            /*
             * Savepoint names, like the TransactionState block itself, live
             * in TopTransactionContext.
             */
            if (name)
                s->name = MemoryContextStrdup(TopTransactionContext, name);
            break;

            /* These cases are invalid. */
        case TBLOCK_DEFAULT:
        case TBLOCK_STARTED:
        case TBLOCK_BEGIN:
        case TBLOCK_SUBBEGIN:
        case TBLOCK_END:
        case TBLOCK_SUBRELEASE:
        case TBLOCK_SUBCOMMIT:
        case TBLOCK_ABORT:
        case TBLOCK_SUBABORT:
        case TBLOCK_ABORT_END:
        case TBLOCK_SUBABORT_END:
        case TBLOCK_ABORT_PENDING:
        case TBLOCK_SUBABORT_PENDING:
        case TBLOCK_SUBRESTART:
        case TBLOCK_SUBABORT_RESTART:
        case TBLOCK_PREPARE:
            elog(FATAL, "DefineSavepoint: unexpected state %s",
                 BlockStateAsString(s->blockState));
            break;
    }
}

/*
 * ReleaseSavepoint
 *      This executes a RELEASE command.
 *
 * As above, we don't actually do anything here except change blockState.
 */
void
ReleaseSavepoint(List *options)
{
    TransactionState s = CurrentTransactionState;
    TransactionState target,
                xact;
    ListCell   *cell;
    char       *name = NULL;

    switch (s->blockState)
    {
            /*
             * We can't rollback to a savepoint if there is no savepoint
             * defined.
             */
        case TBLOCK_INPROGRESS:
            ereport(ERROR,
                    (errcode(ERRCODE_S_E_INVALID_SPECIFICATION),
                     errmsg("no such savepoint")));
            break;

            /*
             * We are in a non-aborted subtransaction.  This is the only valid
             * case.
             */
        case TBLOCK_SUBINPROGRESS:
            break;

            /* These cases are invalid. */
        case TBLOCK_DEFAULT:
        case TBLOCK_STARTED:
        case TBLOCK_BEGIN:
        case TBLOCK_SUBBEGIN:
        case TBLOCK_END:
        case TBLOCK_SUBRELEASE:
        case TBLOCK_SUBCOMMIT:
        case TBLOCK_ABORT:
        case TBLOCK_SUBABORT:
        case TBLOCK_ABORT_END:
        case TBLOCK_SUBABORT_END:
        case TBLOCK_ABORT_PENDING:
        case TBLOCK_SUBABORT_PENDING:
        case TBLOCK_SUBRESTART:
        case TBLOCK_SUBABORT_RESTART:
        case TBLOCK_PREPARE:
            elog(FATAL, "ReleaseSavepoint: unexpected state %s",
                 BlockStateAsString(s->blockState));
            break;
    }

    foreach(cell, options)
    {
        DefElem    *elem = lfirst(cell);

        if (strcmp(elem->defname, "savepoint_name") == 0)
            name = strVal(elem->arg);
    }

    Assert(PointerIsValid(name));

    for (target = s; PointerIsValid(target); target = target->parent)
    {
        if (PointerIsValid(target->name) && strcmp(target->name, name) == 0)
            break;
    }

    if (!PointerIsValid(target))
        ereport(ERROR,
                (errcode(ERRCODE_S_E_INVALID_SPECIFICATION),
                 errmsg("no such savepoint")));

    /* disallow crossing savepoint level boundaries */
    if (target->savepointLevel != s->savepointLevel)
        ereport(ERROR,
                (errcode(ERRCODE_S_E_INVALID_SPECIFICATION),
                 errmsg("no such savepoint")));

    /*
     * Mark "commit pending" all subtransactions up to the target
     * subtransaction.  The actual commits will happen when control gets to
     * CommitTransactionCommand.
     */
    xact = CurrentTransactionState;
    for (;;)
    {
        Assert(xact->blockState == TBLOCK_SUBINPROGRESS);
        xact->blockState = TBLOCK_SUBRELEASE;
        if (xact == target)
            break;
        xact = xact->parent;
        Assert(PointerIsValid(xact));
    }
}

/*
 * RollbackToSavepoint
 *      This executes a ROLLBACK TO <savepoint> command.
 *
 * As above, we don't actually do anything here except change blockState.
 */
void
RollbackToSavepoint(List *options)
{
    TransactionState s = CurrentTransactionState;
    TransactionState target,
                xact;
    ListCell   *cell;
    char       *name = NULL;

    switch (s->blockState)
    {
            /*
             * We can't rollback to a savepoint if there is no savepoint
             * defined.
             */
        case TBLOCK_INPROGRESS:
        case TBLOCK_ABORT:
            ereport(ERROR,
                    (errcode(ERRCODE_S_E_INVALID_SPECIFICATION),
                     errmsg("no such savepoint")));
            break;

            /*
             * There is at least one savepoint, so proceed.
             */
        case TBLOCK_SUBINPROGRESS:
        case TBLOCK_SUBABORT:
            break;

            /* These cases are invalid. */
        case TBLOCK_DEFAULT:
        case TBLOCK_STARTED:
        case TBLOCK_BEGIN:
        case TBLOCK_SUBBEGIN:
        case TBLOCK_END:
        case TBLOCK_SUBRELEASE:
        case TBLOCK_SUBCOMMIT:
        case TBLOCK_ABORT_END:
        case TBLOCK_SUBABORT_END:
        case TBLOCK_ABORT_PENDING:
        case TBLOCK_SUBABORT_PENDING:
        case TBLOCK_SUBRESTART:
        case TBLOCK_SUBABORT_RESTART:
        case TBLOCK_PREPARE:
            elog(FATAL, "RollbackToSavepoint: unexpected state %s",
                 BlockStateAsString(s->blockState));
            break;
    }

    foreach(cell, options)
    {
        DefElem    *elem = lfirst(cell);

        if (strcmp(elem->defname, "savepoint_name") == 0)
            name = strVal(elem->arg);
    }

    Assert(PointerIsValid(name));

    for (target = s; PointerIsValid(target); target = target->parent)
    {
        if (PointerIsValid(target->name) && strcmp(target->name, name) == 0)
            break;
    }

    if (!PointerIsValid(target))
        ereport(ERROR,
                (errcode(ERRCODE_S_E_INVALID_SPECIFICATION),
                 errmsg("no such savepoint")));

    /* disallow crossing savepoint level boundaries */
    if (target->savepointLevel != s->savepointLevel)
        ereport(ERROR,
                (errcode(ERRCODE_S_E_INVALID_SPECIFICATION),
                 errmsg("no such savepoint")));

    /*
     * Mark "abort pending" all subtransactions up to the target
     * subtransaction.  The actual aborts will happen when control gets to
     * CommitTransactionCommand.
     */
    xact = CurrentTransactionState;
    for (;;)
    {
        if (xact == target)
            break;
        if (xact->blockState == TBLOCK_SUBINPROGRESS)
            xact->blockState = TBLOCK_SUBABORT_PENDING;
        else if (xact->blockState == TBLOCK_SUBABORT)
            xact->blockState = TBLOCK_SUBABORT_END;
        else
            elog(FATAL, "RollbackToSavepoint: unexpected state %s",
                 BlockStateAsString(xact->blockState));
        xact = xact->parent;
        Assert(PointerIsValid(xact));
    }

    /* And mark the target as "restart pending" */
    if (xact->blockState == TBLOCK_SUBINPROGRESS)
        xact->blockState = TBLOCK_SUBRESTART;
    else if (xact->blockState == TBLOCK_SUBABORT)
        xact->blockState = TBLOCK_SUBABORT_RESTART;
    else
        elog(FATAL, "RollbackToSavepoint: unexpected state %s",
             BlockStateAsString(xact->blockState));
}

/*
 * BeginInternalSubTransaction
 *      This is the same as DefineSavepoint except it allows TBLOCK_STARTED,
 *      TBLOCK_END, and TBLOCK_PREPARE states, and therefore it can safely be
 *      used in functions that might be called when not inside a BEGIN block
 *      or when running deferred triggers at COMMIT/PREPARE time.  Also, it
 *      automatically does CommitTransactionCommand/StartTransactionCommand
 *      instead of expecting the caller to do it.
 */
void
BeginInternalSubTransaction(char *name)
{
    TransactionState s = CurrentTransactionState;

    switch (s->blockState)
    {
        case TBLOCK_STARTED:
        case TBLOCK_INPROGRESS:
        case TBLOCK_END:
        case TBLOCK_PREPARE:
        case TBLOCK_SUBINPROGRESS:
            /* Normal subtransaction start */
            PushTransaction();
            s = CurrentTransactionState;        /* changed by push */

            /*
             * Savepoint names, like the TransactionState block itself, live
             * in TopTransactionContext.
             */
            if (name)
                s->name = MemoryContextStrdup(TopTransactionContext, name);
            break;

            /* These cases are invalid. */
        case TBLOCK_DEFAULT:
        case TBLOCK_BEGIN:
        case TBLOCK_SUBBEGIN:
        case TBLOCK_SUBRELEASE:
        case TBLOCK_SUBCOMMIT:
        case TBLOCK_ABORT:
        case TBLOCK_SUBABORT:
        case TBLOCK_ABORT_END:
        case TBLOCK_SUBABORT_END:
        case TBLOCK_ABORT_PENDING:
        case TBLOCK_SUBABORT_PENDING:
        case TBLOCK_SUBRESTART:
        case TBLOCK_SUBABORT_RESTART:
            elog(FATAL, "BeginInternalSubTransaction: unexpected state %s",
                 BlockStateAsString(s->blockState));
            break;
    }

    CommitTransactionCommand();
    StartTransactionCommand();
}

/*
 * ReleaseCurrentSubTransaction
 *
 * RELEASE (ie, commit) the innermost subtransaction, regardless of its
 * savepoint name (if any).
 * NB: do NOT use CommitTransactionCommand/StartTransactionCommand with this.
 */
void
ReleaseCurrentSubTransaction(void)
{
    TransactionState s = CurrentTransactionState;

    if (s->blockState != TBLOCK_SUBINPROGRESS)
        elog(ERROR, "ReleaseCurrentSubTransaction: unexpected state %s",
             BlockStateAsString(s->blockState));
    Assert(s->state == TRANS_INPROGRESS);
    MemoryContextSwitchTo(CurTransactionContext);
    CommitSubTransaction();
    s = CurrentTransactionState;    /* changed by pop */
    Assert(s->state == TRANS_INPROGRESS);
}

/*
 * RollbackAndReleaseCurrentSubTransaction
 *
 * ROLLBACK and RELEASE (ie, abort) the innermost subtransaction, regardless
 * of its savepoint name (if any).
 * NB: do NOT use CommitTransactionCommand/StartTransactionCommand with this.
 */
void
RollbackAndReleaseCurrentSubTransaction(void)
{
    TransactionState s = CurrentTransactionState;

    switch (s->blockState)
    {
            /* Must be in a subtransaction */
        case TBLOCK_SUBINPROGRESS:
        case TBLOCK_SUBABORT:
            break;

            /* These cases are invalid. */
        case TBLOCK_DEFAULT:
        case TBLOCK_STARTED:
        case TBLOCK_BEGIN:
        case TBLOCK_SUBBEGIN:
        case TBLOCK_INPROGRESS:
        case TBLOCK_END:
        case TBLOCK_SUBRELEASE:
        case TBLOCK_SUBCOMMIT:
        case TBLOCK_ABORT:
        case TBLOCK_ABORT_END:
        case TBLOCK_SUBABORT_END:
        case TBLOCK_ABORT_PENDING:
        case TBLOCK_SUBABORT_PENDING:
        case TBLOCK_SUBRESTART:
        case TBLOCK_SUBABORT_RESTART:
        case TBLOCK_PREPARE:
            elog(FATAL, "RollbackAndReleaseCurrentSubTransaction: unexpected state %s",
                 BlockStateAsString(s->blockState));
            break;
    }

    /*
     * Abort the current subtransaction, if needed.
     */
    if (s->blockState == TBLOCK_SUBINPROGRESS)
        AbortSubTransaction();

    /* And clean it up, too */
    CleanupSubTransaction();

    s = CurrentTransactionState;    /* changed by pop */
    AssertState(s->blockState == TBLOCK_SUBINPROGRESS ||
                s->blockState == TBLOCK_INPROGRESS ||
                s->blockState == TBLOCK_STARTED);
}

/*
 *  AbortOutOfAnyTransaction
 *
 *  This routine is provided for error recovery purposes.  It aborts any
 *  active transaction or transaction block, leaving the system in a known
 *  idle state.
 */
void
AbortOutOfAnyTransaction(void)
{
    TransactionState s = CurrentTransactionState;

    /*
     * Get out of any transaction or nested transaction
     */
    do
    {
        switch (s->blockState)
        {
            case TBLOCK_DEFAULT:
                if (s->state == TRANS_DEFAULT)
                {
                    /* Not in a transaction, do nothing */
                }
                else
                {
                    /*
                     * We can get here after an error during transaction start
                     * (state will be TRANS_START).  Need to clean up the
                     * incompletely started transaction.  First, adjust the
                     * low-level state to suppress warning message from
                     * AbortTransaction.
                     */
                    if (s->state == TRANS_START)
                        s->state = TRANS_INPROGRESS;
                    AbortTransaction();
                    CleanupTransaction();
                }
                break;
            case TBLOCK_STARTED:
            case TBLOCK_BEGIN:
            case TBLOCK_INPROGRESS:
            case TBLOCK_END:
            case TBLOCK_ABORT_PENDING:
            case TBLOCK_PREPARE:
                /* In a transaction, so clean up */
                AbortTransaction();
                CleanupTransaction();
                s->blockState = TBLOCK_DEFAULT;
                break;
            case TBLOCK_ABORT:
            case TBLOCK_ABORT_END:
                /* AbortTransaction already done, still need Cleanup */
                CleanupTransaction();
                s->blockState = TBLOCK_DEFAULT;
                break;

                /*
                 * In a subtransaction, so clean it up and abort parent too
                 */
            case TBLOCK_SUBBEGIN:
            case TBLOCK_SUBINPROGRESS:
            case TBLOCK_SUBRELEASE:
            case TBLOCK_SUBCOMMIT:
            case TBLOCK_SUBABORT_PENDING:
            case TBLOCK_SUBRESTART:
                AbortSubTransaction();
                CleanupSubTransaction();
                s = CurrentTransactionState;    /* changed by pop */
                break;

            case TBLOCK_SUBABORT:
            case TBLOCK_SUBABORT_END:
            case TBLOCK_SUBABORT_RESTART:
                /* As above, but AbortSubTransaction already done */
                CleanupSubTransaction();
                s = CurrentTransactionState;    /* changed by pop */
                break;
        }
    } while (s->blockState != TBLOCK_DEFAULT);

    /* Should be out of all subxacts now */
    Assert(s->parent == NULL);
}

/*
 * IsTransactionBlock --- are we within a transaction block?
 */
bool
IsTransactionBlock(void)
{
    TransactionState s = CurrentTransactionState;

    if (s->blockState == TBLOCK_DEFAULT || s->blockState == TBLOCK_STARTED)
        return false;

    return true;
}

/*
 * IsTransactionOrTransactionBlock --- are we within either a transaction
 * or a transaction block?  (The backend is only really "idle" when this
 * returns false.)
 *
 * This should match up with IsTransactionBlock and IsTransactionState.
 */
bool
IsTransactionOrTransactionBlock(void)
{
    TransactionState s = CurrentTransactionState;

    if (s->blockState == TBLOCK_DEFAULT)
        return false;

    return true;
}

/*
 * TransactionBlockStatusCode - return status code to send in ReadyForQuery
 */
char
TransactionBlockStatusCode(void)
{
    TransactionState s = CurrentTransactionState;

    switch (s->blockState)
    {
        case TBLOCK_DEFAULT:
        case TBLOCK_STARTED:
            return 'I';         /* idle --- not in transaction */
        case TBLOCK_BEGIN:
        case TBLOCK_SUBBEGIN:
        case TBLOCK_INPROGRESS:
        case TBLOCK_SUBINPROGRESS:
        case TBLOCK_END:
        case TBLOCK_SUBRELEASE:
        case TBLOCK_SUBCOMMIT:
        case TBLOCK_PREPARE:
            return 'T';         /* in transaction */
        case TBLOCK_ABORT:
        case TBLOCK_SUBABORT:
        case TBLOCK_ABORT_END:
        case TBLOCK_SUBABORT_END:
        case TBLOCK_ABORT_PENDING:
        case TBLOCK_SUBABORT_PENDING:
        case TBLOCK_SUBRESTART:
        case TBLOCK_SUBABORT_RESTART:
            return 'E';         /* in failed transaction */
    }

    /* should never get here */
    elog(FATAL, "invalid transaction block state: %s",
         BlockStateAsString(s->blockState));
    return 0;                   /* keep compiler quiet */
}

/*
 * IsSubTransaction
 */
bool
IsSubTransaction(void)
{
    TransactionState s = CurrentTransactionState;

    if (s->nestingLevel >= 2)
        return true;

    return false;
}

/*
 * StartSubTransaction
 *
 * If you're wondering why this is separate from PushTransaction: it's because
 * we can't conveniently do this stuff right inside DefineSavepoint.  The
 * SAVEPOINT utility command will be executed inside a Portal, and if we
 * muck with CurrentMemoryContext or CurrentResourceOwner then exit from
 * the Portal will undo those settings.  So we make DefineSavepoint just
 * push a dummy transaction block, and when control returns to the main
 * idle loop, CommitTransactionCommand will be called, and we'll come here
 * to finish starting the subtransaction.
 */
static void
StartSubTransaction(void)
{
    TransactionState s = CurrentTransactionState;

    if (s->state != TRANS_DEFAULT)
        elog(WARNING, "StartSubTransaction while in %s state",
             TransStateAsString(s->state));

    s->state = TRANS_START;

    /*
     * Initialize subsystems for new subtransaction
     *
     * must initialize resource-management stuff first
     */
    AtSubStart_Memory();
    AtSubStart_ResourceOwner();
    AtSubStart_Inval();
    AtSubStart_Notify();
    AfterTriggerBeginSubXact();

    s->state = TRANS_INPROGRESS;

    /*
     * Call start-of-subxact callbacks
     */
    CallSubXactCallbacks(SUBXACT_EVENT_START_SUB, s->subTransactionId,
                         s->parent->subTransactionId);

    ShowTransactionState("StartSubTransaction");
}

/*
 * CommitSubTransaction
 *
 *  The caller has to make sure to always reassign CurrentTransactionState
 *  if it has a local pointer to it after calling this function.
 */
static void
CommitSubTransaction(void)
{
    TransactionState s = CurrentTransactionState;

    ShowTransactionState("CommitSubTransaction");

    if (s->state != TRANS_INPROGRESS)
        elog(WARNING, "CommitSubTransaction while in %s state",
             TransStateAsString(s->state));

    /* Pre-commit processing goes here */

    CallSubXactCallbacks(SUBXACT_EVENT_PRE_COMMIT_SUB, s->subTransactionId,
                         s->parent->subTransactionId);

    /* Do the actual "commit", such as it is */
    s->state = TRANS_COMMIT;

    /* Must CCI to ensure commands of subtransaction are seen as done */
    CommandCounterIncrement();

    /*
     * Prior to 8.4 we marked subcommit in clog at this point.  We now only
     * perform that step, if required, as part of the atomic update of the
     * whole transaction tree at top level commit or abort.
     */

    /* Post-commit cleanup */
    if (TransactionIdIsValid(s->transactionId))
        AtSubCommit_childXids();
    AfterTriggerEndSubXact(true);
    AtSubCommit_Portals(s->subTransactionId,
                        s->parent->subTransactionId,
                        s->parent->curTransactionOwner);
    AtEOSubXact_LargeObject(true, s->subTransactionId,
                            s->parent->subTransactionId);
    AtSubCommit_Notify();

    CallSubXactCallbacks(SUBXACT_EVENT_COMMIT_SUB, s->subTransactionId,
                         s->parent->subTransactionId);

    ResourceOwnerRelease(s->curTransactionOwner,
                         RESOURCE_RELEASE_BEFORE_LOCKS,
                         true, false);
    AtEOSubXact_RelationCache(true, s->subTransactionId,
                              s->parent->subTransactionId);
    AtEOSubXact_Inval(true);
    AtSubCommit_smgr();

    /*
     * The only lock we actually release here is the subtransaction XID lock.
     */
    CurrentResourceOwner = s->curTransactionOwner;
    if (TransactionIdIsValid(s->transactionId))
        XactLockTableDelete(s->transactionId);

    /*
     * Other locks should get transferred to their parent resource owner.
     */
    ResourceOwnerRelease(s->curTransactionOwner,
                         RESOURCE_RELEASE_LOCKS,
                         true, false);
    ResourceOwnerRelease(s->curTransactionOwner,
                         RESOURCE_RELEASE_AFTER_LOCKS,
                         true, false);

    AtEOXact_GUC(true, s->gucNestLevel);
    AtEOSubXact_SPI(true, s->subTransactionId);
    AtEOSubXact_on_commit_actions(true, s->subTransactionId,
                                  s->parent->subTransactionId);
    AtEOSubXact_Namespace(true, s->subTransactionId,
                          s->parent->subTransactionId);
    AtEOSubXact_Files(true, s->subTransactionId,
                      s->parent->subTransactionId);
    AtEOSubXact_HashTables(true, s->nestingLevel);
    AtEOSubXact_PgStat(true, s->nestingLevel);
    AtSubCommit_Snapshot(s->nestingLevel);

    /*
     * We need to restore the upper transaction's read-only state, in case the
     * upper is read-write while the child is read-only; GUC will incorrectly
     * think it should leave the child state in place.
     */
    XactReadOnly = s->prevXactReadOnly;

    CurrentResourceOwner = s->parent->curTransactionOwner;
    CurTransactionResourceOwner = s->parent->curTransactionOwner;
    ResourceOwnerDelete(s->curTransactionOwner);
    s->curTransactionOwner = NULL;

    AtSubCommit_Memory();

    s->state = TRANS_DEFAULT;

    PopTransaction();
}

/*
 * AbortSubTransaction
 */
static void
AbortSubTransaction(void)
{
    TransactionState s = CurrentTransactionState;

    /* Prevent cancel/die interrupt while cleaning up */
    HOLD_INTERRUPTS();

    /* Make sure we have a valid memory context and resource owner */
    AtSubAbort_Memory();
    AtSubAbort_ResourceOwner();

    /*
     * Release any LW locks we might be holding as quickly as possible.
     * (Regular locks, however, must be held till we finish aborting.)
     * Releasing LW locks is critical since we might try to grab them again
     * while cleaning up!
     *
     * FIXME This may be incorrect --- Are there some locks we should keep?
     * Buffer locks, for example?  I don't think so but I'm not sure.
     */
    LWLockReleaseAll();

    AbortBufferIO();
    UnlockBuffers();

    LockErrorCleanup();

    /*
     * check the current transaction state
     */
    ShowTransactionState("AbortSubTransaction");

    if (s->state != TRANS_INPROGRESS)
        elog(WARNING, "AbortSubTransaction while in %s state",
             TransStateAsString(s->state));

    s->state = TRANS_ABORT;

    /*
     * Reset user ID which might have been changed transiently.  (See notes in
     * AbortTransaction.)
     */
    SetUserIdAndSecContext(s->prevUser, s->prevSecContext);

    /*
     * We can skip all this stuff if the subxact failed before creating a
     * ResourceOwner...
     */
    if (s->curTransactionOwner)
    {
        AfterTriggerEndSubXact(false);
        AtSubAbort_Portals(s->subTransactionId,
                           s->parent->subTransactionId,
                           s->parent->curTransactionOwner);
        AtEOSubXact_LargeObject(false, s->subTransactionId,
                                s->parent->subTransactionId);
        AtSubAbort_Notify();

        /* Advertise the fact that we aborted in pg_clog. */
        (void) RecordTransactionAbort(true);

        /* Post-abort cleanup */
        if (TransactionIdIsValid(s->transactionId))
            AtSubAbort_childXids();

        CallSubXactCallbacks(SUBXACT_EVENT_ABORT_SUB, s->subTransactionId,
                             s->parent->subTransactionId);

        ResourceOwnerRelease(s->curTransactionOwner,
                             RESOURCE_RELEASE_BEFORE_LOCKS,
                             false, false);
        AtEOSubXact_RelationCache(false, s->subTransactionId,
                                  s->parent->subTransactionId);
        AtEOSubXact_Inval(false);
        ResourceOwnerRelease(s->curTransactionOwner,
                             RESOURCE_RELEASE_LOCKS,
                             false, false);
        ResourceOwnerRelease(s->curTransactionOwner,
                             RESOURCE_RELEASE_AFTER_LOCKS,
                             false, false);
        AtSubAbort_smgr();

        AtEOXact_GUC(false, s->gucNestLevel);
        AtEOSubXact_SPI(false, s->subTransactionId);
        AtEOSubXact_on_commit_actions(false, s->subTransactionId,
                                      s->parent->subTransactionId);
        AtEOSubXact_Namespace(false, s->subTransactionId,
                              s->parent->subTransactionId);
        AtEOSubXact_Files(false, s->subTransactionId,
                          s->parent->subTransactionId);
        AtEOSubXact_HashTables(false, s->nestingLevel);
        AtEOSubXact_PgStat(false, s->nestingLevel);
        AtSubAbort_Snapshot(s->nestingLevel);
    }

    /*
     * Restore the upper transaction's read-only state, too.  This should be
     * redundant with GUC's cleanup but we may as well do it for consistency
     * with the commit case.
     */
    XactReadOnly = s->prevXactReadOnly;

    RESUME_INTERRUPTS();
}

/*
 * CleanupSubTransaction
 *
 *  The caller has to make sure to always reassign CurrentTransactionState
 *  if it has a local pointer to it after calling this function.
 */
static void
CleanupSubTransaction(void)
{
    TransactionState s = CurrentTransactionState;

    ShowTransactionState("CleanupSubTransaction");

    if (s->state != TRANS_ABORT)
        elog(WARNING, "CleanupSubTransaction while in %s state",
             TransStateAsString(s->state));

    AtSubCleanup_Portals(s->subTransactionId);

    CurrentResourceOwner = s->parent->curTransactionOwner;
    CurTransactionResourceOwner = s->parent->curTransactionOwner;
    if (s->curTransactionOwner)
        ResourceOwnerDelete(s->curTransactionOwner);
    s->curTransactionOwner = NULL;

    AtSubCleanup_Memory();

    s->state = TRANS_DEFAULT;

    PopTransaction();
}

/*
 * PushTransaction
 *      Create transaction state stack entry for a subtransaction
 *
 *  The caller has to make sure to always reassign CurrentTransactionState
 *  if it has a local pointer to it after calling this function.
 */
static void
PushTransaction(void)
{
    TransactionState p = CurrentTransactionState;
    TransactionState s;

    /*
     * We keep subtransaction state nodes in TopTransactionContext.
     */
    s = (TransactionState)
        MemoryContextAllocZero(TopTransactionContext,
                               sizeof(TransactionStateData));

    /*
     * Assign a subtransaction ID, watching out for counter wraparound.
     */
    currentSubTransactionId += 1;
    if (currentSubTransactionId == InvalidSubTransactionId)
    {
        currentSubTransactionId -= 1;
        pfree(s);
        ereport(ERROR,
                (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                 errmsg("cannot have more than 2^32-1 subtransactions in a transaction")));
    }

    /*
     * We can now stack a minimally valid subtransaction without fear of
     * failure.
     */
    s->transactionId = InvalidTransactionId;    /* until assigned */
    s->subTransactionId = currentSubTransactionId;
    s->parent = p;
    s->nestingLevel = p->nestingLevel + 1;
    s->gucNestLevel = NewGUCNestLevel();
    s->savepointLevel = p->savepointLevel;
    s->state = TRANS_DEFAULT;
    s->blockState = TBLOCK_SUBBEGIN;
    GetUserIdAndSecContext(&s->prevUser, &s->prevSecContext);
    s->prevXactReadOnly = XactReadOnly;

    CurrentTransactionState = s;

    /*
     * AbortSubTransaction and CleanupSubTransaction have to be able to cope
     * with the subtransaction from here on out; in particular they should not
     * assume that it necessarily has a transaction context, resource owner,
     * or XID.
     */
}

/*
 * PopTransaction
 *      Pop back to parent transaction state
 *
 *  The caller has to make sure to always reassign CurrentTransactionState
 *  if it has a local pointer to it after calling this function.
 */
static void
PopTransaction(void)
{
    TransactionState s = CurrentTransactionState;

    if (s->state != TRANS_DEFAULT)
        elog(WARNING, "PopTransaction while in %s state",
             TransStateAsString(s->state));

    if (s->parent == NULL)
        elog(FATAL, "PopTransaction with no parent");

    CurrentTransactionState = s->parent;

    /* Let's just make sure CurTransactionContext is good */
    CurTransactionContext = s->parent->curTransactionContext;
    MemoryContextSwitchTo(CurTransactionContext);

    /* Ditto for ResourceOwner links */
    CurTransactionResourceOwner = s->parent->curTransactionOwner;
    CurrentResourceOwner = s->parent->curTransactionOwner;

    /* Free the old child structure */
    if (s->name)
        pfree(s->name);
    pfree(s);
}

/*
 * ShowTransactionState
 *      Debug support
 */
static void
ShowTransactionState(const char *str)
{
    /* skip work if message will definitely not be printed */
    if (log_min_messages <= DEBUG3 || client_min_messages <= DEBUG3)
    {
        elog(DEBUG3, "%s", str);
        ShowTransactionStateRec(CurrentTransactionState);
    }
}

/*
 * ShowTransactionStateRec
 *      Recursive subroutine for ShowTransactionState
 */
static void
ShowTransactionStateRec(TransactionState s)
{
    StringInfoData buf;

    initStringInfo(&buf);

    if (s->nChildXids > 0)
    {
        int         i;

        appendStringInfo(&buf, "%u", s->childXids[0]);
        for (i = 1; i < s->nChildXids; i++)
            appendStringInfo(&buf, " %u", s->childXids[i]);
    }

    if (s->parent)
        ShowTransactionStateRec(s->parent);

    /* use ereport to suppress computation if msg will not be printed */
    ereport(DEBUG3,
            (errmsg_internal("name: %s; blockState: %13s; state: %7s, xid/subid/cid: %u/%u/%u%s, nestlvl: %d, children: %s",
                             PointerIsValid(s->name) ? s->name : "unnamed",
                             BlockStateAsString(s->blockState),
                             TransStateAsString(s->state),
                             (unsigned int) s->transactionId,
                             (unsigned int) s->subTransactionId,
                             (unsigned int) currentCommandId,
                             currentCommandIdUsed ? " (used)" : "",
                             s->nestingLevel, buf.data)));

    pfree(buf.data);
}

/*
 * BlockStateAsString
 *      Debug support
 */
static const char *
BlockStateAsString(TBlockState blockState)
{
    switch (blockState)
    {
        case TBLOCK_DEFAULT:
            return "DEFAULT";
        case TBLOCK_STARTED:
            return "STARTED";
        case TBLOCK_BEGIN:
            return "BEGIN";
        case TBLOCK_INPROGRESS:
            return "INPROGRESS";
        case TBLOCK_END:
            return "END";
        case TBLOCK_ABORT:
            return "ABORT";
        case TBLOCK_ABORT_END:
            return "ABORT END";
        case TBLOCK_ABORT_PENDING:
            return "ABORT PEND";
        case TBLOCK_PREPARE:
            return "PREPARE";
        case TBLOCK_SUBBEGIN:
            return "SUB BEGIN";
        case TBLOCK_SUBINPROGRESS:
            return "SUB INPROGRS";
        case TBLOCK_SUBRELEASE:
            return "SUB RELEASE";
        case TBLOCK_SUBCOMMIT:
            return "SUB COMMIT";
        case TBLOCK_SUBABORT:
            return "SUB ABORT";
        case TBLOCK_SUBABORT_END:
            return "SUB ABORT END";
        case TBLOCK_SUBABORT_PENDING:
            return "SUB ABRT PEND";
        case TBLOCK_SUBRESTART:
            return "SUB RESTART";
        case TBLOCK_SUBABORT_RESTART:
            return "SUB AB RESTRT";
    }
    return "UNRECOGNIZED";
}

/*
 * TransStateAsString
 *      Debug support
 */
static const char *
TransStateAsString(TransState state)
{
    switch (state)
    {
        case TRANS_DEFAULT:
            return "DEFAULT";
        case TRANS_START:
            return "START";
        case TRANS_INPROGRESS:
            return "INPROGR";
        case TRANS_COMMIT:
            return "COMMIT";
        case TRANS_ABORT:
            return "ABORT";
        case TRANS_PREPARE:
            return "PREPARE";
    }
    return "UNRECOGNIZED";
}

/*
 * xactGetCommittedChildren
 *
 * Gets the list of committed children of the current transaction.  The return
 * value is the number of child transactions.  *ptr is set to point to an
 * array of TransactionIds.  The array is allocated in TopTransactionContext;
 * the caller should *not* pfree() it (this is a change from pre-8.4 code!).
 * If there are no subxacts, *ptr is set to NULL.
 */
int
xactGetCommittedChildren(TransactionId **ptr)
{
    TransactionState s = CurrentTransactionState;

    if (s->nChildXids == 0)
        *ptr = NULL;
    else
        *ptr = s->childXids;

    return s->nChildXids;
}

/*
 *  XLOG support routines
 */

/*
 * Before 9.0 this was a fairly short function, but now it performs many
 * actions for which the order of execution is critical.
 */
static void
xact_redo_commit_internal(TransactionId xid, XLogRecPtr lsn,
                          TransactionId *sub_xids, int nsubxacts,
                          SharedInvalidationMessage *inval_msgs, int nmsgs,
                          RelFileNode *xnodes, int nrels,
                          Oid dbId, Oid tsId,
                          uint32 xinfo)
{
    TransactionId max_xid;
    int         i;

    max_xid = TransactionIdLatest(xid, nsubxacts, sub_xids);

    /*
     * Make sure nextXid is beyond any XID mentioned in the record.
     *
     * We don't expect anyone else to modify nextXid, hence we don't need to
     * hold a lock while checking this. We still acquire the lock to modify
     * it, though.
     */
    if (TransactionIdFollowsOrEquals(max_xid,
                                     ShmemVariableCache->nextXid))
    {
        LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
        ShmemVariableCache->nextXid = max_xid;
        TransactionIdAdvance(ShmemVariableCache->nextXid);
        LWLockRelease(XidGenLock);
    }

    if (standbyState == STANDBY_DISABLED)
    {
        /*
         * Mark the transaction committed in pg_clog.
         */
        TransactionIdCommitTree(xid, nsubxacts, sub_xids);
    }
    else
    {
        /*
         * If a transaction completion record arrives that has as-yet
         * unobserved subtransactions then this will not have been fully
         * handled by the call to RecordKnownAssignedTransactionIds() in the
         * main recovery loop in xlog.c. So we need to do bookkeeping again to
         * cover that case. This is confusing and it is easy to think this
         * call is irrelevant, which has happened three times in development
         * already. Leave it in.
         */
        RecordKnownAssignedTransactionIds(max_xid);

        /*
         * Mark the transaction committed in pg_clog. We use async commit
         * protocol during recovery to provide information on database
         * consistency for when users try to set hint bits. It is important
         * that we do not set hint bits until the minRecoveryPoint is past
         * this commit record. This ensures that if we crash we don't see hint
         * bits set on changes made by transactions that haven't yet
         * recovered. It's unlikely but it's good to be safe.
         */
        TransactionIdAsyncCommitTree(xid, nsubxacts, sub_xids, lsn);

        /*
         * We must mark clog before we update the ProcArray.
         */
        ExpireTreeKnownAssignedTransactionIds(xid, nsubxacts, sub_xids, max_xid);

        /*
         * Send any cache invalidations attached to the commit. We must
         * maintain the same order of invalidation then release locks as
         * occurs in CommitTransaction().
         */
        ProcessCommittedInvalidationMessages(inval_msgs, nmsgs,
                                  XactCompletionRelcacheInitFileInval(xinfo),
                                             dbId, tsId);

        /*
         * Release locks, if any. We do this for both two phase and normal one
         * phase transactions. In effect we are ignoring the prepare phase and
         * just going straight to lock release. At commit we release all locks
         * via their top-level xid only, so no need to provide subxact list,
         * which will save time when replaying commits.
         */
        StandbyReleaseLockTree(xid, 0, NULL);
    }

    /* Make sure files supposed to be dropped are dropped */
    if (nrels > 0)
    {
        /*
         * First update minimum recovery point to cover this WAL record. Once
         * a relation is deleted, there's no going back. The buffer manager
         * enforces the WAL-first rule for normal updates to relation files,
         * so that the minimum recovery point is always updated before the
         * corresponding change in the data file is flushed to disk, but we
         * have to do the same here since we're bypassing the buffer manager.
         *
         * Doing this before deleting the files means that if a deletion fails
         * for some reason, you cannot start up the system even after restart,
         * until you fix the underlying situation so that the deletion will
         * succeed. Alternatively, we could update the minimum recovery point
         * after deletion, but that would leave a small window where the
         * WAL-first rule would be violated.
         */
        XLogFlush(lsn);

        for (i = 0; i < nrels; i++)
        {
            SMgrRelation srel = smgropen(xnodes[i], InvalidBackendId);
            ForkNumber  fork;

            for (fork = 0; fork <= MAX_FORKNUM; fork++)
                XLogDropRelation(xnodes[i], fork);
            smgrdounlink(srel, true);
            smgrclose(srel);
        }
    }

    /*
     * We issue an XLogFlush() for the same reason we emit ForceSyncCommit()
     * in normal operation. For example, in CREATE DATABASE, we copy all files
     * from the template database, and then commit the transaction. If we
     * crash after all the files have been copied but before the commit, you
     * have files in the data directory without an entry in pg_database. To
     * minimize the window
     * for that, we use ForceSyncCommit() to rush the commit record to disk as
     * quick as possible. We have the same window during recovery, and forcing
     * an XLogFlush() (which updates minRecoveryPoint during recovery) helps
     * to reduce that problem window, for any user that requested
     * ForceSyncCommit().
     */
    if (XactCompletionForceSyncCommit(xinfo))
        XLogFlush(lsn);

}

/*
 * Utility function to call xact_redo_commit_internal after breaking down xlrec
 */
static void
xact_redo_commit(xl_xact_commit *xlrec,
                 TransactionId xid, XLogRecPtr lsn)
{
    TransactionId *subxacts;
    SharedInvalidationMessage *inval_msgs;

    /* subxid array follows relfilenodes */
    subxacts = (TransactionId *) &(xlrec->xnodes[xlrec->nrels]);
    /* invalidation messages array follows subxids */
    inval_msgs = (SharedInvalidationMessage *) &(subxacts[xlrec->nsubxacts]);

    xact_redo_commit_internal(xid, lsn, subxacts, xlrec->nsubxacts,
                              inval_msgs, xlrec->nmsgs,
                              xlrec->xnodes, xlrec->nrels,
                              xlrec->dbId,
                              xlrec->tsId,
                              xlrec->xinfo);
}

/*
 * Utility function to call xact_redo_commit_internal  for compact form of message.
 */
static void
xact_redo_commit_compact(xl_xact_commit_compact *xlrec,
                         TransactionId xid, XLogRecPtr lsn)
{
    xact_redo_commit_internal(xid, lsn, xlrec->subxacts, xlrec->nsubxacts,
                              NULL, 0,  /* inval msgs */
                              NULL, 0,  /* relfilenodes */
                              InvalidOid,       /* dbId */
                              InvalidOid,       /* tsId */
                              0);       /* xinfo */
}

/*
 * Be careful with the order of execution, as with xact_redo_commit().
 * The two functions are similar but differ in key places.
 *
 * Note also that an abort can be for a subtransaction and its children,
 * not just for a top level abort. That means we have to consider
 * topxid != xid, whereas in commit we would find topxid == xid always
 * because subtransaction commit is never WAL logged.
 */
static void
xact_redo_abort(xl_xact_abort *xlrec, TransactionId xid)
{
    TransactionId *sub_xids;
    TransactionId max_xid;
    int         i;

    sub_xids = (TransactionId *) &(xlrec->xnodes[xlrec->nrels]);
    max_xid = TransactionIdLatest(xid, xlrec->nsubxacts, sub_xids);

    /*
     * Make sure nextXid is beyond any XID mentioned in the record.
     *
     * We don't expect anyone else to modify nextXid, hence we don't need to
     * hold a lock while checking this. We still acquire the lock to modify
     * it, though.
     */
    if (TransactionIdFollowsOrEquals(max_xid,
                                     ShmemVariableCache->nextXid))
    {
        LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
        ShmemVariableCache->nextXid = max_xid;
        TransactionIdAdvance(ShmemVariableCache->nextXid);
        LWLockRelease(XidGenLock);
    }

    if (standbyState == STANDBY_DISABLED)
    {
        /* Mark the transaction aborted in pg_clog, no need for async stuff */
        TransactionIdAbortTree(xid, xlrec->nsubxacts, sub_xids);
    }
    else
    {
        /*
         * If a transaction completion record arrives that has as-yet
         * unobserved subtransactions then this will not have been fully
         * handled by the call to RecordKnownAssignedTransactionIds() in the
         * main recovery loop in xlog.c. So we need to do bookkeeping again to
         * cover that case. This is confusing and it is easy to think this
         * call is irrelevant, which has happened three times in development
         * already. Leave it in.
         */
        RecordKnownAssignedTransactionIds(max_xid);

        /* Mark the transaction aborted in pg_clog, no need for async stuff */
        TransactionIdAbortTree(xid, xlrec->nsubxacts, sub_xids);

        /*
         * We must update the ProcArray after we have marked clog.
         */
        ExpireTreeKnownAssignedTransactionIds(xid, xlrec->nsubxacts, sub_xids, max_xid);

        /*
         * There are no flat files that need updating, nor invalidation
         * messages to send or undo.
         */

        /*
         * Release locks, if any. There are no invalidations to send.
         */
        StandbyReleaseLockTree(xid, xlrec->nsubxacts, sub_xids);
    }

    /* Make sure files supposed to be dropped are dropped */
    for (i = 0; i < xlrec->nrels; i++)
    {
        SMgrRelation srel = smgropen(xlrec->xnodes[i], InvalidBackendId);
        ForkNumber  fork;

        for (fork = 0; fork <= MAX_FORKNUM; fork++)
            XLogDropRelation(xlrec->xnodes[i], fork);
        smgrdounlink(srel, true);
        smgrclose(srel);
    }
}

void
xact_redo(XLogRecPtr lsn, XLogRecord *record)
{
    uint8       info = record->xl_info & ~XLR_INFO_MASK;

    /* Backup blocks are not used in xact records */
    Assert(!(record->xl_info & XLR_BKP_BLOCK_MASK));

    if (info == XLOG_XACT_COMMIT_COMPACT)
    {
        xl_xact_commit_compact *xlrec = (xl_xact_commit_compact *) XLogRecGetData(record);

        xact_redo_commit_compact(xlrec, record->xl_xid, lsn);
    }
    else if (info == XLOG_XACT_COMMIT)
    {
        xl_xact_commit *xlrec = (xl_xact_commit *) XLogRecGetData(record);

        xact_redo_commit(xlrec, record->xl_xid, lsn);
    }
    else if (info == XLOG_XACT_ABORT)
    {
        xl_xact_abort *xlrec = (xl_xact_abort *) XLogRecGetData(record);

        xact_redo_abort(xlrec, record->xl_xid);
    }
    else if (info == XLOG_XACT_PREPARE)
    {
        /* the record contents are exactly the 2PC file */
        RecreateTwoPhaseFile(record->xl_xid,
                             XLogRecGetData(record), record->xl_len);
    }
    else if (info == XLOG_XACT_COMMIT_PREPARED)
    {
        xl_xact_commit_prepared *xlrec = (xl_xact_commit_prepared *) XLogRecGetData(record);

        xact_redo_commit(&xlrec->crec, xlrec->xid, lsn);
        RemoveTwoPhaseFile(xlrec->xid, false);
    }
    else if (info == XLOG_XACT_ABORT_PREPARED)
    {
        xl_xact_abort_prepared *xlrec = (xl_xact_abort_prepared *) XLogRecGetData(record);

        xact_redo_abort(&xlrec->arec, xlrec->xid);
        RemoveTwoPhaseFile(xlrec->xid, false);
    }
    else if (info == XLOG_XACT_ASSIGNMENT)
    {
        xl_xact_assignment *xlrec = (xl_xact_assignment *) XLogRecGetData(record);

        if (standbyState >= STANDBY_INITIALIZED)
            ProcArrayApplyXidAssignment(xlrec->xtop,
                                        xlrec->nsubxacts, xlrec->xsub);
    }
    else
        elog(PANIC, "xact_redo: unknown op code %u", info);
}