Tweak code so that pg_subtrans is never consulted for XIDs older than
RecentXmin (== MyProc->xmin). This ensures that it will be safe to truncate pg_subtrans at RecentGlobalXmin, which should largely eliminate any fear of bloat. Along the way, eliminate SubTransXidsHaveCommonAncestor, which isn't really needed and could not give a trustworthy result anyway under the lookback restriction. In an unrelated but nearby change, #ifdef out GetUndoRecPtr, which has been dead code since 2001 and seems unlikely to ever be resurrected.
This commit is contained in:
Tom Lane
parent
37d937ea2c
commit
f009c316ba
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@ -15,7 +15,7 @@
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* Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $PostgreSQL: pgsql/src/backend/access/transam/subtrans.c,v 1.1 2004/07/01 00:49:42 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/access/transam/subtrans.c,v 1.2 2004/08/22 02:41:57 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -30,6 +30,7 @@
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#include "access/subtrans.h"
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#include "miscadmin.h"
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#include "storage/lwlock.h"
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#include "utils/tqual.h"
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/*
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@ -113,6 +114,9 @@ SubTransGetParent(TransactionId xid)
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TransactionId *ptr;
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TransactionId parent;
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/* Can't ask about stuff that might not be around anymore */
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Assert(TransactionIdFollowsOrEquals(xid, RecentXmin));
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/* Bootstrap and frozen XIDs have no parent */
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if (!TransactionIdIsNormal(xid))
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return InvalidTransactionId;
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@ -133,6 +137,13 @@ SubTransGetParent(TransactionId xid)
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* SubTransGetTopmostTransaction
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*
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* Returns the topmost transaction of the given transaction id.
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*
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* Because we cannot look back further than RecentXmin, it is possible
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* that this function will lie and return an intermediate subtransaction ID
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* instead of the true topmost parent ID. This is OK, because in practice
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* we only care about detecting whether the topmost parent is still running
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* or is part of a current snapshot's list of still-running transactions.
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* Therefore, any XID before RecentXmin is as good as any other.
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*/
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TransactionId
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SubTransGetTopmostTransaction(TransactionId xid)
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@ -140,9 +151,14 @@ SubTransGetTopmostTransaction(TransactionId xid)
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TransactionId parentXid = xid,
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previousXid = xid;
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/* Can't ask about stuff that might not be around anymore */
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Assert(TransactionIdFollowsOrEquals(xid, RecentXmin));
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while (TransactionIdIsValid(parentXid))
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{
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previousXid = parentXid;
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if (TransactionIdPrecedes(parentXid, RecentXmin))
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break;
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parentXid = SubTransGetParent(parentXid);
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}
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@ -151,30 +167,6 @@ SubTransGetTopmostTransaction(TransactionId xid)
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return previousXid;
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}
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/*
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* SubTransXidsHaveCommonAncestor
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*
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* Returns true iff the Xids have a common ancestor
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*/
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bool
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SubTransXidsHaveCommonAncestor(TransactionId xid1, TransactionId xid2)
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{
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if (TransactionIdEquals(xid1, xid2))
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return true;
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while (TransactionIdIsValid(xid1) && TransactionIdIsValid(xid2))
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{
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if (TransactionIdPrecedes(xid2, xid1))
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xid1 = SubTransGetParent(xid1);
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else
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xid2 = SubTransGetParent(xid2);
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if (TransactionIdEquals(xid1, xid2))
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return true;
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}
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return false;
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}
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/*
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* Initialization of shared memory for Subtrans
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@ -8,7 +8,7 @@
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*
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/access/transam/transam.c,v 1.57 2004/07/01 00:49:42 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/access/transam/transam.c,v 1.58 2004/08/22 02:41:57 tgl Exp $
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*
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* NOTES
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* This file contains the high level access-method interface to the
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@ -22,6 +22,7 @@
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#include "access/clog.h"
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#include "access/subtrans.h"
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#include "access/transam.h"
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#include "utils/tqual.h"
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/* ----------------
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@ -199,11 +200,15 @@ TransactionIdDidCommit(TransactionId transactionId)
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/*
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* If it's marked subcommitted, we have to check the parent recursively.
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* However, if it's older than RecentXmin, we can't look at pg_subtrans;
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* instead assume that the parent crashed without cleaning up its children.
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*/
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if (xidstatus == TRANSACTION_STATUS_SUB_COMMITTED)
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{
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TransactionId parentXid;
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if (TransactionIdPrecedes(transactionId, RecentXmin))
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return false;
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parentXid = SubTransGetParent(transactionId);
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Assert(TransactionIdIsValid(parentXid));
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return TransactionIdDidCommit(parentXid);
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@ -243,24 +248,17 @@ TransactionIdDidAbort(TransactionId transactionId)
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/*
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* If it's marked subcommitted, we have to check the parent recursively.
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*
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* If we detect that the parent has aborted, update pg_clog to show the
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* subtransaction as aborted. This is only needed when the parent
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* crashed before either committing or aborting. We want to clean up
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* pg_clog so future visitors don't need to make this check again.
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* However, if it's older than RecentXmin, we can't look at pg_subtrans;
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* instead assume that the parent crashed without cleaning up its children.
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*/
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if (xidstatus == TRANSACTION_STATUS_SUB_COMMITTED)
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{
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TransactionId parentXid;
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bool parentAborted;
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if (TransactionIdPrecedes(transactionId, RecentXmin))
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return true;
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parentXid = SubTransGetParent(transactionId);
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parentAborted = TransactionIdDidAbort(parentXid);
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if (parentAborted)
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TransactionIdAbort(transactionId);
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return parentAborted;
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return TransactionIdDidAbort(parentXid);
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}
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/*
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@ -8,7 +8,7 @@
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*
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/storage/ipc/sinval.c,v 1.68 2004/08/15 17:03:36 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/storage/ipc/sinval.c,v 1.69 2004/08/22 02:41:57 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -526,7 +526,7 @@ TransactionIdIsInProgress(TransactionId xid)
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/*
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* Don't bother checking a very old transaction.
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*/
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if (TransactionIdPrecedes(xid, RecentGlobalXmin))
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if (TransactionIdPrecedes(xid, RecentXmin))
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{
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xc_by_recent_xmin_inc();
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return false;
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@ -912,6 +912,7 @@ CountActiveBackends(void)
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return count;
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}
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#ifdef NOT_USED
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/*
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* GetUndoRecPtr -- returns oldest PGPROC->logRec.
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*/
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@ -947,6 +948,7 @@ GetUndoRecPtr(void)
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return (urec);
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}
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#endif /* NOT_USED */
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/*
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* BackendIdGetProc - given a BackendId, find its PGPROC structure
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@ -8,7 +8,7 @@
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*
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/storage/lmgr/lmgr.c,v 1.66 2004/07/28 14:23:29 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/storage/lmgr/lmgr.c,v 1.67 2004/08/22 02:41:57 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -345,7 +345,7 @@ XactLockTableWait(TransactionId xid)
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LOCKTAG tag;
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TransactionId myxid = GetTopTransactionId();
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Assert(!SubTransXidsHaveCommonAncestor(xid, myxid));
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Assert(!TransactionIdEquals(xid, myxid));
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MemSet(&tag, 0, sizeof(tag));
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tag.relId = XactLockTableId;
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@ -16,7 +16,7 @@
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/utils/time/tqual.c,v 1.74 2004/07/28 14:23:30 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/utils/time/tqual.c,v 1.75 2004/08/22 02:41:57 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -933,8 +933,6 @@ HeapTupleSatisfiesVacuum(HeapTupleHeader tuple, TransactionId OldestXmin)
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{
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if (tuple->t_infomask & HEAP_XMAX_INVALID) /* xid invalid */
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return HEAPTUPLE_INSERT_IN_PROGRESS;
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Assert(SubTransXidsHaveCommonAncestor(HeapTupleHeaderGetXmin(tuple),
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HeapTupleHeaderGetXmax(tuple)));
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if (tuple->t_infomask & HEAP_MARKED_FOR_UPDATE)
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return HEAPTUPLE_INSERT_IN_PROGRESS;
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/* inserted and then deleted by same xact */
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@ -1008,7 +1006,7 @@ HeapTupleSatisfiesVacuum(HeapTupleHeader tuple, TransactionId OldestXmin)
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* Deleter committed, but check special cases.
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*/
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if (SubTransXidsHaveCommonAncestor(HeapTupleHeaderGetXmin(tuple),
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if (TransactionIdEquals(HeapTupleHeaderGetXmin(tuple),
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HeapTupleHeaderGetXmax(tuple)))
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{
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/*
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@ -6,7 +6,7 @@
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* Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $PostgreSQL: pgsql/src/include/access/subtrans.h,v 1.1 2004/07/01 00:51:38 tgl Exp $
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* $PostgreSQL: pgsql/src/include/access/subtrans.h,v 1.2 2004/08/22 02:41:58 tgl Exp $
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*/
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#ifndef SUBTRANS_H
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#define SUBTRANS_H
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@ -20,7 +20,6 @@
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extern void SubTransSetParent(TransactionId xid, TransactionId parent);
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extern TransactionId SubTransGetParent(TransactionId xid);
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extern TransactionId SubTransGetTopmostTransaction(TransactionId xid);
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extern bool SubTransXidsHaveCommonAncestor(TransactionId xid1, TransactionId xid2);
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extern int SUBTRANSShmemSize(void);
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extern void SUBTRANSShmemInit(void);
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@ -6,7 +6,7 @@
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* Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $PostgreSQL: pgsql/src/include/access/xlog.h,v 1.54 2004/07/21 22:31:25 tgl Exp $
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* $PostgreSQL: pgsql/src/include/access/xlog.h,v 1.55 2004/08/22 02:41:58 tgl Exp $
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*/
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#ifndef XLOG_H
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#define XLOG_H
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@ -135,9 +135,4 @@ extern void CreateCheckPoint(bool shutdown, bool force);
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extern void XLogPutNextOid(Oid nextOid);
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extern XLogRecPtr GetRedoRecPtr(void);
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/* in storage/ipc/sinval.c, but don't want to declare in sinval.h because
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* we'd have to include xlog.h into that ...
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*/
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extern XLogRecPtr GetUndoRecPtr(void);
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#endif /* XLOG_H */
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