transam.h

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * transam.h
 *    postgres transaction access method support code
 *
 *
 * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/access/transam.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef TRANSAM_H
#define TRANSAM_H

#include "access/xlogdefs.h"


/* ----------------
 *      Special transaction ID values
 *
 * BootstrapTransactionId is the XID for "bootstrap" operations, and
 * FrozenTransactionId is used for very old tuples.  Both should
 * always be considered valid.
 *
 * FirstNormalTransactionId is the first "normal" transaction id.
 * Note: if you need to change it, you must change pg_class.h as well.
 * ----------------
 */
#define InvalidTransactionId        ((TransactionId) 0)
#define BootstrapTransactionId      ((TransactionId) 1)
#define FrozenTransactionId         ((TransactionId) 2)
#define FirstNormalTransactionId    ((TransactionId) 3)
#define MaxTransactionId            ((TransactionId) 0xFFFFFFFF)

/* ----------------
 *      transaction ID manipulation macros
 * ----------------
 */
#define TransactionIdIsValid(xid)       ((xid) != InvalidTransactionId)
#define TransactionIdIsNormal(xid)      ((xid) >= FirstNormalTransactionId)
#define TransactionIdEquals(id1, id2)   ((id1) == (id2))
#define TransactionIdStore(xid, dest)   (*(dest) = (xid))
#define StoreInvalidTransactionId(dest) (*(dest) = InvalidTransactionId)

/* advance a transaction ID variable, handling wraparound correctly */
#define TransactionIdAdvance(dest)  \
    do { \
        (dest)++; \
        if ((dest) < FirstNormalTransactionId) \
            (dest) = FirstNormalTransactionId; \
    } while(0)

/* back up a transaction ID variable, handling wraparound correctly */
#define TransactionIdRetreat(dest)  \
    do { \
        (dest)--; \
    } while ((dest) < FirstNormalTransactionId)

/* compare two XIDs already known to be normal; this is a macro for speed */
#define NormalTransactionIdPrecedes(id1, id2) \
    (AssertMacro(TransactionIdIsNormal(id1) && TransactionIdIsNormal(id2)), \
    (int32) ((id1) - (id2)) < 0)

/* ----------
 *      Object ID (OID) zero is InvalidOid.
 *
 *      OIDs 1-9999 are reserved for manual assignment (see the files
 *      in src/include/catalog/).
 *
 *      OIDS 10000-16383 are reserved for assignment during initdb
 *      using the OID generator.  (We start the generator at 10000.)
 *
 *      OIDs beginning at 16384 are assigned from the OID generator
 *      during normal multiuser operation.  (We force the generator up to
 *      16384 as soon as we are in normal operation.)
 *
 * The choices of 10000 and 16384 are completely arbitrary, and can be moved
 * if we run low on OIDs in either category.  Changing the macros below
 * should be sufficient to do this.
 *
 * NOTE: if the OID generator wraps around, we skip over OIDs 0-16383
 * and resume with 16384.  This minimizes the odds of OID conflict, by not
 * reassigning OIDs that might have been assigned during initdb.
 * ----------
 */
#define FirstBootstrapObjectId  10000
#define FirstNormalObjectId     16384

/*
 * VariableCache is a data structure in shared memory that is used to track
 * OID and XID assignment state.  For largely historical reasons, there is
 * just one struct with different fields that are protected by different
 * LWLocks.
 *
 * Note: xidWrapLimit and oldestXidDB are not "active" values, but are
 * used just to generate useful messages when xidWarnLimit or xidStopLimit
 * are exceeded.
 */
typedef struct VariableCacheData
{
    /*
     * These fields are protected by OidGenLock.
     */
    Oid         nextOid;        /* next OID to assign */
    uint32      oidCount;       /* OIDs available before must do XLOG work */

    /*
     * These fields are protected by XidGenLock.
     */
    TransactionId nextXid;      /* next XID to assign */

    TransactionId oldestXid;    /* cluster-wide minimum datfrozenxid */
    TransactionId xidVacLimit;  /* start forcing autovacuums here */
    TransactionId xidWarnLimit; /* start complaining here */
    TransactionId xidStopLimit; /* refuse to advance nextXid beyond here */
    TransactionId xidWrapLimit; /* where the world ends */
    Oid         oldestXidDB;    /* database with minimum datfrozenxid */

    /*
     * These fields are protected by ProcArrayLock.
     */
    TransactionId latestCompletedXid;   /* newest XID that has committed or
                                         * aborted */
} VariableCacheData;

typedef VariableCacheData *VariableCache;


/* ----------------
 *      extern declarations
 * ----------------
 */

/* in transam/xact.c */
extern bool TransactionStartedDuringRecovery(void);

/* in transam/varsup.c */
extern PGDLLIMPORT VariableCache ShmemVariableCache;

/*
 * prototypes for functions in transam/transam.c
 */
extern bool TransactionIdDidCommit(TransactionId transactionId);
extern bool TransactionIdDidAbort(TransactionId transactionId);
extern bool TransactionIdIsKnownCompleted(TransactionId transactionId);
extern void TransactionIdAbort(TransactionId transactionId);
extern void TransactionIdCommitTree(TransactionId xid, int nxids, TransactionId *xids);
extern void TransactionIdAsyncCommitTree(TransactionId xid, int nxids, TransactionId *xids, XLogRecPtr lsn);
extern void TransactionIdAbortTree(TransactionId xid, int nxids, TransactionId *xids);
extern bool TransactionIdPrecedes(TransactionId id1, TransactionId id2);
extern bool TransactionIdPrecedesOrEquals(TransactionId id1, TransactionId id2);
extern bool TransactionIdFollows(TransactionId id1, TransactionId id2);
extern bool TransactionIdFollowsOrEquals(TransactionId id1, TransactionId id2);
extern TransactionId TransactionIdLatest(TransactionId mainxid,
                    int nxids, const TransactionId *xids);
extern XLogRecPtr TransactionIdGetCommitLSN(TransactionId xid);

/* in transam/varsup.c */
extern TransactionId GetNewTransactionId(bool isSubXact);
extern TransactionId ReadNewTransactionId(void);
extern void SetTransactionIdLimit(TransactionId oldest_datfrozenxid,
                      Oid oldest_datoid);
extern bool ForceTransactionIdLimitUpdate(void);
extern Oid  GetNewObjectId(void);

#endif   /* TRAMSAM_H */