Header And Logo
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#include "postgres.h"#include "access/clog.h"#include "access/subtrans.h"#include "access/transam.h"#include "access/xact.h"#include "commands/dbcommands.h"#include "miscadmin.h"#include "postmaster/autovacuum.h"#include "storage/pmsignal.h"#include "storage/proc.h"#include "utils/syscache.h"
Go to the source code of this file.
Defines | |
| #define | VAR_OID_PREFETCH 8192 |
Functions | |
| TransactionId | GetNewTransactionId (bool isSubXact) |
| TransactionId | ReadNewTransactionId (void) |
| void | SetTransactionIdLimit (TransactionId oldest_datfrozenxid, Oid oldest_datoid) |
| bool | ForceTransactionIdLimitUpdate (void) |
| Oid | GetNewObjectId (void) |
Variables | |
| VariableCache | ShmemVariableCache = NULL |
| #define VAR_OID_PREFETCH 8192 |
Definition at line 29 of file varsup.c.
Referenced by GetNewObjectId().
| bool ForceTransactionIdLimitUpdate | ( | void | ) |
Definition at line 397 of file varsup.c.
References DATABASEOID, LW_SHARED, LWLockAcquire(), LWLockRelease(), VariableCacheData::nextXid, ObjectIdGetDatum, VariableCacheData::oldestXid, VariableCacheData::oldestXidDB, SearchSysCacheExists1, TransactionIdFollowsOrEquals(), TransactionIdIsNormal, TransactionIdIsValid, XidGenLock, and VariableCacheData::xidVacLimit.
Referenced by vac_update_datfrozenxid().
{
TransactionId nextXid;
TransactionId xidVacLimit;
TransactionId oldestXid;
Oid oldestXidDB;
/* Locking is probably not really necessary, but let's be careful */
LWLockAcquire(XidGenLock, LW_SHARED);
nextXid = ShmemVariableCache->nextXid;
xidVacLimit = ShmemVariableCache->xidVacLimit;
oldestXid = ShmemVariableCache->oldestXid;
oldestXidDB = ShmemVariableCache->oldestXidDB;
LWLockRelease(XidGenLock);
if (!TransactionIdIsNormal(oldestXid))
return true; /* shouldn't happen, but just in case */
if (!TransactionIdIsValid(xidVacLimit))
return true; /* this shouldn't happen anymore either */
if (TransactionIdFollowsOrEquals(nextXid, xidVacLimit))
return true; /* past VacLimit, don't delay updating */
if (!SearchSysCacheExists1(DATABASEOID, ObjectIdGetDatum(oldestXidDB)))
return true; /* could happen, per comments above */
return false;
}
| Oid GetNewObjectId | ( | void | ) |
Definition at line 435 of file varsup.c.
References elog, ERROR, FirstBootstrapObjectId, FirstNormalObjectId, IsPostmasterEnvironment, LW_EXCLUSIVE, LWLockAcquire(), LWLockRelease(), VariableCacheData::nextOid, VariableCacheData::oidCount, OidGenLock, RecoveryInProgress(), VAR_OID_PREFETCH, and XLogPutNextOid().
Referenced by GetNewOid(), GetNewOidWithIndex(), and GetNewRelFileNode().
{
Oid result;
/* safety check, we should never get this far in a HS slave */
if (RecoveryInProgress())
elog(ERROR, "cannot assign OIDs during recovery");
LWLockAcquire(OidGenLock, LW_EXCLUSIVE);
/*
* Check for wraparound of the OID counter. We *must* not return 0
* (InvalidOid); and as long as we have to check that, it seems a good
* idea to skip over everything below FirstNormalObjectId too. (This
* basically just avoids lots of collisions with bootstrap-assigned OIDs
* right after a wrap occurs, so as to avoid a possibly large number of
* iterations in GetNewOid.) Note we are relying on unsigned comparison.
*
* During initdb, we start the OID generator at FirstBootstrapObjectId, so
* we only enforce wrapping to that point when in bootstrap or standalone
* mode. The first time through this routine after normal postmaster
* start, the counter will be forced up to FirstNormalObjectId. This
* mechanism leaves the OIDs between FirstBootstrapObjectId and
* FirstNormalObjectId available for automatic assignment during initdb,
* while ensuring they will never conflict with user-assigned OIDs.
*/
if (ShmemVariableCache->nextOid < ((Oid) FirstNormalObjectId))
{
if (IsPostmasterEnvironment)
{
/* wraparound in normal environment */
ShmemVariableCache->nextOid = FirstNormalObjectId;
ShmemVariableCache->oidCount = 0;
}
else
{
/* we may be bootstrapping, so don't enforce the full range */
if (ShmemVariableCache->nextOid < ((Oid) FirstBootstrapObjectId))
{
/* wraparound in standalone environment? */
ShmemVariableCache->nextOid = FirstBootstrapObjectId;
ShmemVariableCache->oidCount = 0;
}
}
}
/* If we run out of logged for use oids then we must log more */
if (ShmemVariableCache->oidCount == 0)
{
XLogPutNextOid(ShmemVariableCache->nextOid + VAR_OID_PREFETCH);
ShmemVariableCache->oidCount = VAR_OID_PREFETCH;
}
result = ShmemVariableCache->nextOid;
(ShmemVariableCache->nextOid)++;
(ShmemVariableCache->oidCount)--;
LWLockRelease(OidGenLock);
return result;
}
| TransactionId GetNewTransactionId | ( | bool | isSubXact | ) |
Definition at line 46 of file varsup.c.
References Assert, elog, ereport, errcode(), errhint(), errmsg(), ERROR, ExtendCLOG(), ExtendSUBTRANS(), get_database_name(), IsBootstrapProcessingMode, IsUnderPostmaster, LW_EXCLUSIVE, LWLockAcquire(), LWLockRelease(), MyPgXact, MyProc, VariableCacheData::nextXid, PGXACT::nxids, VariableCacheData::oldestXidDB, PGXACT::overflowed, PGPROC_MAX_CACHED_SUBXIDS, PMSIGNAL_START_AUTOVAC_LAUNCHER, RecoveryInProgress(), SendPostmasterSignal(), PGPROC::subxids, TransactionIdAdvance, TransactionIdFollowsOrEquals(), WARNING, PGXACT::xid, XidGenLock, XidCache::xids, VariableCacheData::xidStopLimit, VariableCacheData::xidVacLimit, VariableCacheData::xidWarnLimit, and VariableCacheData::xidWrapLimit.
Referenced by AssignTransactionId().
{
TransactionId xid;
/*
* During bootstrap initialization, we return the special bootstrap
* transaction id.
*/
if (IsBootstrapProcessingMode())
{
Assert(!isSubXact);
MyPgXact->xid = BootstrapTransactionId;
return BootstrapTransactionId;
}
/* safety check, we should never get this far in a HS slave */
if (RecoveryInProgress())
elog(ERROR, "cannot assign TransactionIds during recovery");
LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
xid = ShmemVariableCache->nextXid;
/*----------
* Check to see if it's safe to assign another XID. This protects against
* catastrophic data loss due to XID wraparound. The basic rules are:
*
* If we're past xidVacLimit, start trying to force autovacuum cycles.
* If we're past xidWarnLimit, start issuing warnings.
* If we're past xidStopLimit, refuse to execute transactions, unless
* we are running in a standalone backend (which gives an escape hatch
* to the DBA who somehow got past the earlier defenses).
*
* Note that this coding also appears in GetNewMultiXactId.
*----------
*/
if (TransactionIdFollowsOrEquals(xid, ShmemVariableCache->xidVacLimit))
{
/*
* For safety's sake, we release XidGenLock while sending signals,
* warnings, etc. This is not so much because we care about
* preserving concurrency in this situation, as to avoid any
* possibility of deadlock while doing get_database_name(). First,
* copy all the shared values we'll need in this path.
*/
TransactionId xidWarnLimit = ShmemVariableCache->xidWarnLimit;
TransactionId xidStopLimit = ShmemVariableCache->xidStopLimit;
TransactionId xidWrapLimit = ShmemVariableCache->xidWrapLimit;
Oid oldest_datoid = ShmemVariableCache->oldestXidDB;
LWLockRelease(XidGenLock);
/*
* To avoid swamping the postmaster with signals, we issue the autovac
* request only once per 64K transaction starts. This still gives
* plenty of chances before we get into real trouble.
*/
if (IsUnderPostmaster && (xid % 65536) == 0)
SendPostmasterSignal(PMSIGNAL_START_AUTOVAC_LAUNCHER);
if (IsUnderPostmaster &&
TransactionIdFollowsOrEquals(xid, xidStopLimit))
{
char *oldest_datname = get_database_name(oldest_datoid);
/* complain even if that DB has disappeared */
if (oldest_datname)
ereport(ERROR,
(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
errmsg("database is not accepting commands to avoid wraparound data loss in database \"%s\"",
oldest_datname),
errhint("Stop the postmaster and use a standalone backend to vacuum that database.\n"
"You might also need to commit or roll back old prepared transactions.")));
else
ereport(ERROR,
(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
errmsg("database is not accepting commands to avoid wraparound data loss in database with OID %u",
oldest_datoid),
errhint("Stop the postmaster and use a standalone backend to vacuum that database.\n"
"You might also need to commit or roll back old prepared transactions.")));
}
else if (TransactionIdFollowsOrEquals(xid, xidWarnLimit))
{
char *oldest_datname = get_database_name(oldest_datoid);
/* complain even if that DB has disappeared */
if (oldest_datname)
ereport(WARNING,
(errmsg("database \"%s\" must be vacuumed within %u transactions",
oldest_datname,
xidWrapLimit - xid),
errhint("To avoid a database shutdown, execute a database-wide VACUUM in that database.\n"
"You might also need to commit or roll back old prepared transactions.")));
else
ereport(WARNING,
(errmsg("database with OID %u must be vacuumed within %u transactions",
oldest_datoid,
xidWrapLimit - xid),
errhint("To avoid a database shutdown, execute a database-wide VACUUM in that database.\n"
"You might also need to commit or roll back old prepared transactions.")));
}
/* Re-acquire lock and start over */
LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
xid = ShmemVariableCache->nextXid;
}
/*
* If we are allocating the first XID of a new page of the commit log,
* zero out that commit-log page before returning. We must do this while
* holding XidGenLock, else another xact could acquire and commit a later
* XID before we zero the page. Fortunately, a page of the commit log
* holds 32K or more transactions, so we don't have to do this very often.
*
* Extend pg_subtrans too.
*/
ExtendCLOG(xid);
ExtendSUBTRANS(xid);
/*
* Now advance the nextXid counter. This must not happen until after we
* have successfully completed ExtendCLOG() --- if that routine fails, we
* want the next incoming transaction to try it again. We cannot assign
* more XIDs until there is CLOG space for them.
*/
TransactionIdAdvance(ShmemVariableCache->nextXid);
/*
* We must store the new XID into the shared ProcArray before releasing
* XidGenLock. This ensures that every active XID older than
* latestCompletedXid is present in the ProcArray, which is essential for
* correct OldestXmin tracking; see src/backend/access/transam/README.
*
* XXX by storing xid into MyPgXact without acquiring ProcArrayLock, we
* are relying on fetch/store of an xid to be atomic, else other backends
* might see a partially-set xid here. But holding both locks at once
* would be a nasty concurrency hit. So for now, assume atomicity.
*
* Note that readers of PGXACT xid fields should be careful to fetch the
* value only once, rather than assume they can read a value multiple
* times and get the same answer each time.
*
* The same comments apply to the subxact xid count and overflow fields.
*
* A solution to the atomic-store problem would be to give each PGXACT its
* own spinlock used only for fetching/storing that PGXACT's xid and
* related fields.
*
* If there's no room to fit a subtransaction XID into PGPROC, set the
* cache-overflowed flag instead. This forces readers to look in
* pg_subtrans to map subtransaction XIDs up to top-level XIDs. There is a
* race-condition window, in that the new XID will not appear as running
* until its parent link has been placed into pg_subtrans. However, that
* will happen before anyone could possibly have a reason to inquire about
* the status of the XID, so it seems OK. (Snapshots taken during this
* window *will* include the parent XID, so they will deliver the correct
* answer later on when someone does have a reason to inquire.)
*/
{
/*
* Use volatile pointer to prevent code rearrangement; other backends
* could be examining my subxids info concurrently, and we don't want
* them to see an invalid intermediate state, such as incrementing
* nxids before filling the array entry. Note we are assuming that
* TransactionId and int fetch/store are atomic.
*/
volatile PGPROC *myproc = MyProc;
volatile PGXACT *mypgxact = MyPgXact;
if (!isSubXact)
mypgxact->xid = xid;
else
{
int nxids = mypgxact->nxids;
if (nxids < PGPROC_MAX_CACHED_SUBXIDS)
{
myproc->subxids.xids[nxids] = xid;
mypgxact->nxids = nxids + 1;
}
else
mypgxact->overflowed = true;
}
}
LWLockRelease(XidGenLock);
return xid;
}
| TransactionId ReadNewTransactionId | ( | void | ) |
Definition at line 240 of file varsup.c.
References LW_SHARED, LWLockAcquire(), LWLockRelease(), VariableCacheData::nextXid, and XidGenLock.
Referenced by _bt_pagedel(), AutoVacWorkerMain(), do_start_worker(), GetNextXidAndEpoch(), GetStableLatestTransactionId(), and vacuum_set_xid_limits().
{
TransactionId xid;
LWLockAcquire(XidGenLock, LW_SHARED);
xid = ShmemVariableCache->nextXid;
LWLockRelease(XidGenLock);
return xid;
}
| void SetTransactionIdLimit | ( | TransactionId | oldest_datfrozenxid, | |
| Oid | oldest_datoid | |||
| ) |
Definition at line 257 of file varsup.c.
References Assert, autovacuum_freeze_max_age, DEBUG1, ereport, errhint(), errmsg(), FirstNormalTransactionId, get_database_name(), InRecovery, IsTransactionState(), IsUnderPostmaster, LW_EXCLUSIVE, LWLockAcquire(), LWLockRelease(), MaxTransactionId, VariableCacheData::nextXid, VariableCacheData::oldestXid, VariableCacheData::oldestXidDB, PMSIGNAL_START_AUTOVAC_LAUNCHER, SendPostmasterSignal(), TransactionIdFollowsOrEquals(), TransactionIdIsNormal, WARNING, XidGenLock, VariableCacheData::xidStopLimit, VariableCacheData::xidVacLimit, VariableCacheData::xidWarnLimit, and VariableCacheData::xidWrapLimit.
Referenced by BootStrapXLOG(), StartupXLOG(), vac_truncate_clog(), and xlog_redo().
{
TransactionId xidVacLimit;
TransactionId xidWarnLimit;
TransactionId xidStopLimit;
TransactionId xidWrapLimit;
TransactionId curXid;
Assert(TransactionIdIsNormal(oldest_datfrozenxid));
/*
* The place where we actually get into deep trouble is halfway around
* from the oldest potentially-existing XID. (This calculation is
* probably off by one or two counts, because the special XIDs reduce the
* size of the loop a little bit. But we throw in plenty of slop below,
* so it doesn't matter.)
*/
xidWrapLimit = oldest_datfrozenxid + (MaxTransactionId >> 1);
if (xidWrapLimit < FirstNormalTransactionId)
xidWrapLimit += FirstNormalTransactionId;
/*
* We'll refuse to continue assigning XIDs in interactive mode once we get
* within 1M transactions of data loss. This leaves lots of room for the
* DBA to fool around fixing things in a standalone backend, while not
* being significant compared to total XID space. (Note that since
* vacuuming requires one transaction per table cleaned, we had better be
* sure there's lots of XIDs left...)
*/
xidStopLimit = xidWrapLimit - 1000000;
if (xidStopLimit < FirstNormalTransactionId)
xidStopLimit -= FirstNormalTransactionId;
/*
* We'll start complaining loudly when we get within 10M transactions of
* the stop point. This is kind of arbitrary, but if you let your gas
* gauge get down to 1% of full, would you be looking for the next gas
* station? We need to be fairly liberal about this number because there
* are lots of scenarios where most transactions are done by automatic
* clients that won't pay attention to warnings. (No, we're not gonna make
* this configurable. If you know enough to configure it, you know enough
* to not get in this kind of trouble in the first place.)
*/
xidWarnLimit = xidStopLimit - 10000000;
if (xidWarnLimit < FirstNormalTransactionId)
xidWarnLimit -= FirstNormalTransactionId;
/*
* We'll start trying to force autovacuums when oldest_datfrozenxid gets
* to be more than autovacuum_freeze_max_age transactions old.
*
* Note: guc.c ensures that autovacuum_freeze_max_age is in a sane range,
* so that xidVacLimit will be well before xidWarnLimit.
*
* Note: autovacuum_freeze_max_age is a PGC_POSTMASTER parameter so that
* we don't have to worry about dealing with on-the-fly changes in its
* value. It doesn't look practical to update shared state from a GUC
* assign hook (too many processes would try to execute the hook,
* resulting in race conditions as well as crashes of those not connected
* to shared memory). Perhaps this can be improved someday.
*/
xidVacLimit = oldest_datfrozenxid + autovacuum_freeze_max_age;
if (xidVacLimit < FirstNormalTransactionId)
xidVacLimit += FirstNormalTransactionId;
/* Grab lock for just long enough to set the new limit values */
LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
ShmemVariableCache->oldestXid = oldest_datfrozenxid;
ShmemVariableCache->xidVacLimit = xidVacLimit;
ShmemVariableCache->xidWarnLimit = xidWarnLimit;
ShmemVariableCache->xidStopLimit = xidStopLimit;
ShmemVariableCache->xidWrapLimit = xidWrapLimit;
ShmemVariableCache->oldestXidDB = oldest_datoid;
curXid = ShmemVariableCache->nextXid;
LWLockRelease(XidGenLock);
/* Log the info */
ereport(DEBUG1,
(errmsg("transaction ID wrap limit is %u, limited by database with OID %u",
xidWrapLimit, oldest_datoid)));
/*
* If past the autovacuum force point, immediately signal an autovac
* request. The reason for this is that autovac only processes one
* database per invocation. Once it's finished cleaning up the oldest
* database, it'll call here, and we'll signal the postmaster to start
* another iteration immediately if there are still any old databases.
*/
if (TransactionIdFollowsOrEquals(curXid, xidVacLimit) &&
IsUnderPostmaster && !InRecovery)
SendPostmasterSignal(PMSIGNAL_START_AUTOVAC_LAUNCHER);
/* Give an immediate warning if past the wrap warn point */
if (TransactionIdFollowsOrEquals(curXid, xidWarnLimit) && !InRecovery)
{
char *oldest_datname;
/*
* We can be called when not inside a transaction, for example during
* StartupXLOG(). In such a case we cannot do database access, so we
* must just report the oldest DB's OID.
*
* Note: it's also possible that get_database_name fails and returns
* NULL, for example because the database just got dropped. We'll
* still warn, even though the warning might now be unnecessary.
*/
if (IsTransactionState())
oldest_datname = get_database_name(oldest_datoid);
else
oldest_datname = NULL;
if (oldest_datname)
ereport(WARNING,
(errmsg("database \"%s\" must be vacuumed within %u transactions",
oldest_datname,
xidWrapLimit - curXid),
errhint("To avoid a database shutdown, execute a database-wide VACUUM in that database.\n"
"You might also need to commit or roll back old prepared transactions.")));
else
ereport(WARNING,
(errmsg("database with OID %u must be vacuumed within %u transactions",
oldest_datoid,
xidWrapLimit - curXid),
errhint("To avoid a database shutdown, execute a database-wide VACUUM in that database.\n"
"You might also need to commit or roll back old prepared transactions.")));
}
}
| VariableCache ShmemVariableCache = NULL |
Definition at line 32 of file varsup.c.
Referenced by BootStrapXLOG(), CreateCheckPoint(), ExpireTreeKnownAssignedTransactionIds(), GetOldestActiveTransactionId(), GetOldestXmin(), GetRunningTransactionData(), GetSnapshotData(), InitShmemAllocation(), multixact_redo(), PrescanPreparedTransactions(), ProcArrayApplyRecoveryInfo(), ProcArrayEndTransaction(), ProcArrayRemove(), RecordKnownAssignedTransactionIds(), ReleasePredicateLocks(), StartupCLOG(), StartupSUBTRANS(), StartupXLOG(), TransactionIdIsInProgress(), TrimCLOG(), xact_redo_abort(), xact_redo_commit_internal(), XidCacheRemoveRunningXids(), and xlog_redo().
1.7.1