varsup.c File Reference

#include "postgres.h"
#include "access/clog.h"
#include "access/commit_ts.h"
#include "access/subtrans.h"
#include "access/transam.h"
#include "access/xact.h"
#include "access/xlog.h"
#include "commands/dbcommands.h"
#include "miscadmin.h"
#include "postmaster/autovacuum.h"
#include "storage/pmsignal.h"
#include "storage/proc.h"
#include "utils/syscache.h"

Include dependency graph for varsup.c:

Go to the source code of this file.

Macros
#define	VAR_OID_PREFETCH   8192

Functions
FullTransactionId	GetNewTransactionId (bool isSubXact)
FullTransactionId	ReadNextFullTransactionId (void)
void	AdvanceNextFullTransactionIdPastXid (TransactionId xid)
void	AdvanceOldestClogXid (TransactionId oldest_datfrozenxid)
void	SetTransactionIdLimit (TransactionId oldest_datfrozenxid, Oid oldest_datoid)
bool	ForceTransactionIdLimitUpdate (void)
Oid	GetNewObjectId (void)

Variables
VariableCache	ShmemVariableCache = NULL

Macro Definition Documentation

VAR_OID_PREFETCH

#define VAR_OID_PREFETCH   8192

Definition at line 31 of file varsup.c.

Referenced by GetNewObjectId().

Function Documentation

AdvanceNextFullTransactionIdPastXid()

void AdvanceNextFullTransactionIdPastXid

(

TransactionId

xid

)

Definition at line 277 of file varsup.c.

References AmStartupProcess, Assert, epoch, EpochFromFullTransactionId, FullTransactionIdFromEpochAndXid(), IsUnderPostmaster, LW_EXCLUSIVE, LWLockAcquire(), LWLockRelease(), VariableCacheData::nextXid, TransactionIdAdvance, TransactionIdFollowsOrEquals(), unlikely, and XidFromFullTransactionId.

Referenced by multixact_redo(), ProcArrayApplyRecoveryInfo(), ProcessTwoPhaseBuffer(), RecordKnownAssignedTransactionIds(), StartupXLOG(), xact_redo_abort(), and xact_redo_commit().

{
    FullTransactionId newNextFullXid;
    TransactionId next_xid;
    uint32      epoch;

    /*
     * It is safe to read nextXid without a lock, because this is only
     * called from the startup process or single-process mode, meaning that no
     * other process can modify it.
     */
    Assert(AmStartupProcess() || !IsUnderPostmaster);

    /* Fast return if this isn't an xid high enough to move the needle. */
    next_xid = XidFromFullTransactionId(ShmemVariableCache->nextXid);
    if (!TransactionIdFollowsOrEquals(xid, next_xid))
        return;

    /*
     * Compute the FullTransactionId that comes after the given xid.  To do
     * this, we preserve the existing epoch, but detect when we've wrapped
     * into a new epoch.  This is necessary because WAL records and 2PC state
     * currently contain 32 bit xids.  The wrap logic is safe in those cases
     * because the span of active xids cannot exceed one epoch at any given
     * point in the WAL stream.
     */
    TransactionIdAdvance(xid);
    epoch = EpochFromFullTransactionId(ShmemVariableCache->nextXid);
    if (unlikely(xid < next_xid))
        ++epoch;
    newNextFullXid = FullTransactionIdFromEpochAndXid(epoch, xid);

    /*
     * We still need to take a lock to modify the value when there are
     * concurrent readers.
     */
    LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
    ShmemVariableCache->nextXid = newNextFullXid;
    LWLockRelease(XidGenLock);
}

AdvanceOldestClogXid()

void AdvanceOldestClogXid

(

TransactionId

oldest_datfrozenxid

)

Definition at line 328 of file varsup.c.

References LW_EXCLUSIVE, LWLockAcquire(), LWLockRelease(), VariableCacheData::oldestClogXid, and TransactionIdPrecedes().

Referenced by BootStrapXLOG(), clog_redo(), StartupXLOG(), and TruncateCLOG().

{
    LWLockAcquire(XactTruncationLock, LW_EXCLUSIVE);
    if (TransactionIdPrecedes(ShmemVariableCache->oldestClogXid,
                              oldest_datfrozenxid))
    {
        ShmemVariableCache->oldestClogXid = oldest_datfrozenxid;
    }
    LWLockRelease(XactTruncationLock);
}

ForceTransactionIdLimitUpdate()

bool ForceTransactionIdLimitUpdate

(

void

)

Definition at line 490 of file varsup.c.

References DATABASEOID, LW_SHARED, LWLockAcquire(), LWLockRelease(), VariableCacheData::nextXid, ObjectIdGetDatum, VariableCacheData::oldestXid, VariableCacheData::oldestXidDB, SearchSysCacheExists1, TransactionIdFollowsOrEquals(), TransactionIdIsNormal, TransactionIdIsValid, XidFromFullTransactionId, 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 = XidFromFullTransactionId(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 xidVacLimit, don't delay updating */
    if (!SearchSysCacheExists1(DATABASEOID, ObjectIdGetDatum(oldestXidDB)))
        return true;            /* could happen, per comments above */
    return false;
}

GetNewObjectId()

Oid GetNewObjectId

(

void

)

Definition at line 528 of file varsup.c.

References Assert, AssertTransactionIdInAllowableRange, elog, ERROR, FirstBootstrapObjectId, FirstNormalObjectId, IsPostmasterEnvironment, LW_EXCLUSIVE, LWLockAcquire(), LWLockRelease(), VariableCacheData::nextOid, VariableCacheData::nextXid, VariableCacheData::oidCount, VariableCacheData::oldestXid, pg_memory_barrier, RecoveryInProgress(), TransactionIdFollowsOrEquals(), TransactionIdIsNormal, TransactionIdIsValid, TransactionIdPrecedesOrEquals(), VAR_OID_PREFETCH, XidFromFullTransactionId, and XLogPutNextOid().

Referenced by GetNewOidWithIndex(), and GetNewRelFileNode().

{
    Oid         result;

    /* safety check, we should never get this far in a HS standby */
    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 in normal operation we mustn't return anything below
     * FirstNormalObjectId since that range is reserved for initdb (see
     * IsCatalogRelationOid()).  Note we are relying on unsigned comparison.
     *
     * During initdb, we start the OID generator at FirstBootstrapObjectId, so
     * we only wrap if before 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, or first post-initdb assignment, in normal mode */
            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 mode (unlikely but possible) */
                ShmemVariableCache->nextOid = FirstNormalObjectId;
                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;
}

GetNewTransactionId()

FullTransactionId GetNewTransactionId

(

bool

isSubXact

)

Definition at line 50 of file varsup.c.

References Assert, BootstrapTransactionId, XidCacheStatus::count, elog, ereport, errcode(), errhint(), errmsg(), ERROR, ExtendCLOG(), ExtendCommitTs(), ExtendSUBTRANS(), FullTransactionIdAdvance(), FullTransactionIdFromEpochAndXid(), get_database_name(), IsBootstrapProcessingMode, IsInParallelMode(), IsUnderPostmaster, LW_EXCLUSIVE, LWLockAcquire(), LWLockRelease(), MyProc, VariableCacheData::nextXid, VariableCacheData::oldestXidDB, XidCacheStatus::overflowed, pg_write_barrier, PGPROC_MAX_CACHED_SUBXIDS, PGPROC::pgxactoff, PMSIGNAL_START_AUTOVAC_LAUNCHER, ProcGlobal, RecoveryInProgress(), SendPostmasterSignal(), PGPROC::subxids, PROC_HDR::subxidStates, PGPROC::subxidStatus, TransactionIdFollowsOrEquals(), WARNING, PGPROC::xid, XidFromFullTransactionId, XidCache::xids, PROC_HDR::xids, VariableCacheData::xidStopLimit, VariableCacheData::xidVacLimit, VariableCacheData::xidWarnLimit, and VariableCacheData::xidWrapLimit.

Referenced by AssignTransactionId().

{
    FullTransactionId full_xid;
    TransactionId xid;

    /*
     * Workers synchronize transaction state at the beginning of each parallel
     * operation, so we can't account for new XIDs after that point.
     */
    if (IsInParallelMode())
        elog(ERROR, "cannot assign TransactionIds during a parallel operation");

    /*
     * During bootstrap initialization, we return the special bootstrap
     * transaction id.
     */
    if (IsBootstrapProcessingMode())
    {
        Assert(!isSubXact);
        MyProc->xid = BootstrapTransactionId;
        ProcGlobal->xids[MyProc->pgxactoff] = BootstrapTransactionId;
        return FullTransactionIdFromEpochAndXid(0, BootstrapTransactionId);
    }

    /* safety check, we should never get this far in a HS standby */
    if (RecoveryInProgress())
        elog(ERROR, "cannot assign TransactionIds during recovery");

    LWLockAcquire(XidGenLock, LW_EXCLUSIVE);

    full_xid = ShmemVariableCache->nextXid;
    xid = XidFromFullTransactionId(full_xid);

    /*----------
     * 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 single-user mode (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 vacuum that database in single-user mode.\n"
                                 "You might also need to commit or roll back old prepared transactions, or drop stale replication slots.")));
            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 vacuum that database in single-user mode.\n"
                                 "You might also need to commit or roll back old prepared transactions, or drop stale replication slots.")));
        }
        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, or drop stale replication slots.")));
            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, or drop stale replication slots.")));
        }

        /* Re-acquire lock and start over */
        LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
        full_xid = ShmemVariableCache->nextXid;
        xid = XidFromFullTransactionId(full_xid);
    }

    /*
     * 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 and pg_commit_ts too.
     */
    ExtendCLOG(xid);
    ExtendCommitTs(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.
     */
    FullTransactionIdAdvance(&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.
     *
     * Note that readers of ProcGlobal->xids/PGPROC->xid should be careful
     * to fetch the value for each proc only once, rather than assume they can
     * read a value multiple times and get the same answer each time.  Note we
     * are assuming that TransactionId and int fetch/store are atomic.
     *
     * The same comments apply to the subxact xid count and overflow fields.
     *
     * Use of a write barrier prevents dangerous code rearrangement in this
     * function; other backends could otherwise e.g. be examining my subxids
     * info concurrently, and we don't want them to see an invalid
     * intermediate state, such as an incremented nxids before the array entry
     * is filled.
     *
     * Other processes that read nxids should do so before reading xids
     * elements with a pg_read_barrier() in between, so that they can be sure
     * not to read an uninitialized array element; see
     * src/backend/storage/lmgr/README.barrier.
     *
     * 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.)
     */
    if (!isSubXact)
    {
        Assert(ProcGlobal->subxidStates[MyProc->pgxactoff].count == 0);
        Assert(!ProcGlobal->subxidStates[MyProc->pgxactoff].overflowed);
        Assert(MyProc->subxidStatus.count == 0);
        Assert(!MyProc->subxidStatus.overflowed);

        /* LWLockRelease acts as barrier */
        MyProc->xid = xid;
        ProcGlobal->xids[MyProc->pgxactoff] = xid;
    }
    else
    {
        XidCacheStatus *substat = &ProcGlobal->subxidStates[MyProc->pgxactoff];
        int         nxids = MyProc->subxidStatus.count;

        Assert(substat->count == MyProc->subxidStatus.count);
        Assert(substat->overflowed == MyProc->subxidStatus.overflowed);

        if (nxids < PGPROC_MAX_CACHED_SUBXIDS)
        {
            MyProc->subxids.xids[nxids] = xid;
            pg_write_barrier();
            MyProc->subxidStatus.count = substat->count = nxids + 1;
        }
        else
            MyProc->subxidStatus.overflowed = substat->overflowed = true;
    }

    LWLockRelease(XidGenLock);

    return full_xid;
}

ReadNextFullTransactionId()

FullTransactionId ReadNextFullTransactionId

(

void

)

Definition at line 261 of file varsup.c.

References LW_SHARED, LWLockAcquire(), LWLockRelease(), and VariableCacheData::nextXid.

Referenced by gistdeletepage(), gistRedoPageReuse(), pg_current_snapshot(), ReadNewTransactionId(), TransactionIdInRecentPast(), and XLogWalRcvSendHSFeedback().

{
    FullTransactionId fullXid;

    LWLockAcquire(XidGenLock, LW_SHARED);
    fullXid = ShmemVariableCache->nextXid;
    LWLockRelease(XidGenLock);

    return fullXid;
}

SetTransactionIdLimit()

void SetTransactionIdLimit	(	TransactionId	oldest_datfrozenxid,
		Oid	oldest_datoid
	)

Definition at line 345 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, XidFromFullTransactionId, 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 3M 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. (VACUUM requires an XID
     * if it truncates at wal_level!=minimal.  "VACUUM (ANALYZE)", which a DBA
     * might do by reflex, assigns an XID.  Hence, we had better be sure
     * there's lots of XIDs left...)  Also, at default BLCKSZ, this leaves two
     * completely-idle segments.  In the event of edge-case bugs involving
     * page or segment arithmetic, idle segments render the bugs unreachable
     * outside of single-user mode.
     */
    xidStopLimit = xidWrapLimit - 3000000;
    if (xidStopLimit < FirstNormalTransactionId)
        xidStopLimit -= FirstNormalTransactionId;

    /*
     * We'll start complaining loudly when we get within 40M transactions of
     * data loss.  This is kind of arbitrary, but if you let your gas gauge
     * get down to 2% 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 = xidWrapLimit - 40000000;
    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.  See also
     * SetMultiXactIdLimit.
     */
    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 = XidFromFullTransactionId(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, or drop stale replication slots.")));
        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, or drop stale replication slots.")));
    }
}

Variable Documentation

ShmemVariableCache

VariableCache ShmemVariableCache = NULL

Definition at line 34 of file varsup.c.

Referenced by ActivateCommitTs(), AdvanceOldestCommitTsXid(), BootStrapXLOG(), ComputeXidHorizons(), CreateCheckPoint(), CreateSharedProcArray(), DeactivateCommitTs(), GetOldestActiveTransactionId(), GetOldestSafeDecodingTransactionId(), GetRunningTransactionData(), GetSnapshotData(), GetSnapshotDataReuse(), InitShmemAllocation(), MaintainLatestCompletedXid(), MaintainLatestCompletedXidRecovery(), PostmasterMarkPIDForWorkerNotify(), PrescanPreparedTransactions(), ProcArrayApplyRecoveryInfo(), ProcArrayClearTransaction(), ProcArrayEndTransactionInternal(), ProcArrayRemove(), ProcessTwoPhaseBuffer(), ReleasePredicateLocks(), SetCommitTsLimit(), StartupCLOG(), StartupSUBTRANS(), StartupXLOG(), TransactionIdGetCommitTsData(), TransactionIdInRecentPast(), TransactionIdIsInProgress(), TransactionTreeSetCommitTsData(), TrimCLOG(), xlog_redo(), and XLogRecGetFullXid().