#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:

Macros
#define	VAR_OID_PREFETCH 8192

Functions
TransactionId	GetNewTransactionId (bool isSubXact)

TransactionId	ReadNewTransactionId (void)

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

#define VAR_OID_PREFETCH 8192

Definition at line 31 of file varsup.c.

Referenced by GetNewObjectId().

Function Documentation

void AdvanceOldestClogXid ( TransactionId oldest_datfrozenxid )

Definition at line 271 of file varsup.c.

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

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

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

bool ForceTransactionIdLimitUpdate ( void )

Definition at line 429 of file varsup.c.

References DATABASEOID, LW_SHARED, LWLockAcquire(), LWLockRelease(), VariableCacheData::nextXid, ObjectIdGetDatum, VariableCacheData::oldestXid, VariableCacheData::oldestXidDB, SearchSysCacheExists1, TransactionIdFollowsOrEquals(), TransactionIdIsNormal, TransactionIdIsValid, 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 467 of file varsup.c.

References elog, ERROR, FirstBootstrapObjectId, FirstNormalObjectId, IsPostmasterEnvironment, LW_EXCLUSIVE, LWLockAcquire(), LWLockRelease(), VariableCacheData::nextOid, VariableCacheData::oidCount, RecoveryInProgress(), result, VAR_OID_PREFETCH, and XLogPutNextOid().

Referenced by GetNewOid(), 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 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 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;
 }

TransactionId GetNewTransactionId ( bool isSubXact )

Definition at line 48 of file varsup.c.

References Assert, BootstrapTransactionId, elog, ereport, errcode(), errhint(), errmsg(), ERROR, ExtendCLOG(), ExtendCommitTs(), ExtendSUBTRANS(), get_database_name(), IsBootstrapProcessingMode, IsInParallelMode(), 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, XidCache::xids, VariableCacheData::xidStopLimit, VariableCacheData::xidVacLimit, VariableCacheData::xidWarnLimit, and VariableCacheData::xidWrapLimit.

Referenced by AssignTransactionId().

 {
     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);
         MyPgXact->xid = BootstrapTransactionId;
         return 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);
 
     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 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.")));
             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.")));
         }
         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 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.
      */
     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 250 of file varsup.c.

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

Referenced by _bt_unlink_halfdead_page(), ActivateCommitTs(), AutoVacWorkerMain(), do_start_worker(), GetNextXidAndEpoch(), GetStableLatestTransactionId(), vac_truncate_clog(), vac_update_datfrozenxid(), vac_update_relstats(), 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 288 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, NULL, VariableCacheData::oldestXid, VariableCacheData::oldestXidDB, PMSIGNAL_START_AUTOVAC_LAUNCHER, SendPostmasterSignal(), TransactionIdFollowsOrEquals(), TransactionIdIsNormal, WARNING, 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.  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 = 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.")));
     }
 }

Variable Documentation

VariableCache ShmemVariableCache = NULL

Definition at line 34 of file varsup.c.

Referenced by ActivateCommitTs(), AdvanceOldestCommitTsXid(), BootStrapXLOG(), CreateCheckPoint(), DeactivateCommitTs(), ExpireTreeKnownAssignedTransactionIds(), GetOldestActiveTransactionId(), GetOldestSafeDecodingTransactionId(), GetOldestXmin(), GetRunningTransactionData(), GetSnapshotData(), InitShmemAllocation(), multixact_redo(), PrescanPreparedTransactions(), ProcArrayApplyRecoveryInfo(), ProcArrayEndTransactionInternal(), ProcArrayRemove(), ProcessTwoPhaseBuffer(), RecordKnownAssignedTransactionIds(), ReleasePredicateLocks(), SetCommitTsLimit(), StartupCLOG(), StartupSUBTRANS(), StartupXLOG(), TransactionIdGetCommitTsData(), TransactionIdInRecentPast(), TransactionIdIsInProgress(), TransactionTreeSetCommitTsData(), TrimCLOG(), xact_redo_abort(), xact_redo_commit(), XidCacheRemoveRunningXids(), and xlog_redo().

Macros

Functions

Variables

Macro Definition Documentation

Function Documentation

Variable Documentation