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RecentXmin is too recent to use as the cutoff point for accessing
pg_subtrans --- what we need is the oldest xmin of any snapshot in use in the current top transaction. Introduce a new variable TransactionXmin to play this role. Fixes intermittent regression failure reported by Neil Conway.
This commit is contained in:
Tom Lane
parent
8f9f198603
commit
86fff990b2
@ -22,7 +22,7 @@
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* Portions Copyright (c) 1996-2004, 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 1.5 2004/08/29 05:06:40 momjian Exp $
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* $PostgreSQL: pgsql/src/backend/access/transam/subtrans.c,v 1.6 2004/09/16 18:35:20 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -105,7 +105,7 @@ SubTransGetParent(TransactionId xid)
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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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Assert(TransactionIdFollowsOrEquals(xid, TransactionXmin));
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/* Bootstrap and frozen XIDs have no parent */
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if (!TransactionIdIsNormal(xid))
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@ -129,12 +129,12 @@ SubTransGetParent(TransactionId xid)
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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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* Because we cannot look back further than TransactionXmin, 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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* Therefore, any XID before TransactionXmin 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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@ -143,12 +143,12 @@ SubTransGetTopmostTransaction(TransactionId 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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Assert(TransactionIdFollowsOrEquals(xid, TransactionXmin));
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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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if (TransactionIdPrecedes(parentXid, TransactionXmin))
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break;
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parentXid = SubTransGetParent(parentXid);
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}
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@ -312,7 +312,7 @@ ExtendSUBTRANS(TransactionId newestXact)
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* Remove all SUBTRANS segments before the one holding the passed transaction ID
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*
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* This is normally called during checkpoint, with oldestXact being the
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* oldest XMIN of any running transaction.
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* oldest TransactionXmin of any running transaction.
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*/
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void
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TruncateSUBTRANS(TransactionId oldestXact)
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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 1.61 2004/08/29 05:06:40 momjian Exp $
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* $PostgreSQL: pgsql/src/backend/access/transam/transam.c,v 1.62 2004/09/16 18:35:20 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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@ -200,15 +200,15 @@ TransactionIdDidCommit(TransactionId transactionId)
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/*
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* If it's marked subcommitted, we have to check the parent
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* recursively. However, if it's older than RecentXmin, we can't look
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* at pg_subtrans; instead assume that the parent crashed without
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* recursively. However, if it's older than TransactionXmin, we can't
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* look at pg_subtrans; instead assume that the parent crashed without
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* 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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if (TransactionIdPrecedes(transactionId, TransactionXmin))
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return false;
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parentXid = SubTransGetParent(transactionId);
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Assert(TransactionIdIsValid(parentXid));
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@ -249,15 +249,15 @@ TransactionIdDidAbort(TransactionId transactionId)
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/*
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* If it's marked subcommitted, we have to check the parent
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* recursively. However, if it's older than RecentXmin, we can't look
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* at pg_subtrans; instead assume that the parent crashed without
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* recursively. However, if it's older than TransactionXmin, we can't
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* look at pg_subtrans; instead assume that the parent crashed without
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* 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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if (TransactionIdPrecedes(transactionId, TransactionXmin))
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return true;
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parentXid = SubTransGetParent(transactionId);
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Assert(TransactionIdIsValid(parentXid));
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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 1.73 2004/09/06 23:33:35 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/storage/ipc/sinval.c,v 1.74 2004/09/16 18:35:21 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -521,7 +521,8 @@ TransactionIdIsInProgress(TransactionId xid)
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bool locked;
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/*
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* Don't bother checking a very old transaction.
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* Don't bother checking a transaction older than RecentXmin; it
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* could not possibly still be running.
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*/
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if (TransactionIdPrecedes(xid, RecentXmin))
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{
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@ -732,10 +733,19 @@ GetOldestXmin(bool allDbs)
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* This ensures that the set of transactions seen as "running" by the
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* current xact will not change after it takes the snapshot.
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*
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* We also compute the current global xmin (oldest xmin across all running
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* transactions) and save it in RecentGlobalXmin. This is the same
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* computation done by GetOldestXmin(TRUE). The xmin value is also stored
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* into RecentXmin.
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* Note that only top-level XIDs are included in the snapshot. We can
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* still apply the xmin and xmax limits to subtransaction XIDs, but we
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* need to work a bit harder to see if XIDs in [xmin..xmax) are running.
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*
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* We also update the following backend-global variables:
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* TransactionXmin: the oldest xmin of any snapshot in use in the
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* current transaction (this is the same as MyProc->xmin). This
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* is just the xmin computed for the first, serializable snapshot.
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* RecentXmin: the xmin computed for the most recent snapshot. XIDs
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* older than this are known not running any more.
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* RecentGlobalXmin: the global xmin (oldest TransactionXmin across all
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* running transactions). This is the same computation done by
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* GetOldestXmin(TRUE).
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*----------
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*/
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Snapshot
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@ -751,6 +761,11 @@ GetSnapshotData(Snapshot snapshot, bool serializable)
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Assert(snapshot != NULL);
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/* Serializable snapshot must be computed before any other... */
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Assert(serializable ?
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!TransactionIdIsValid(MyProc->xmin) :
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TransactionIdIsValid(MyProc->xmin));
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/*
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* Allocating space for MaxBackends xids is usually overkill;
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* lastBackend would be sufficient. But it seems better to do the
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@ -850,13 +865,10 @@ GetSnapshotData(Snapshot snapshot, bool serializable)
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}
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if (serializable)
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MyProc->xmin = xmin;
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MyProc->xmin = TransactionXmin = xmin;
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LWLockRelease(SInvalLock);
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/* Serializable snapshot must be computed before any other... */
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Assert(TransactionIdIsValid(MyProc->xmin));
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/*
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* Update globalxmin to include actual process xids. This is a
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* slightly different way of computing it than GetOldestXmin uses, but
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@ -865,7 +877,7 @@ GetSnapshotData(Snapshot snapshot, bool serializable)
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if (TransactionIdPrecedes(xmin, globalxmin))
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globalxmin = xmin;
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/* Update globals for use by VACUUM */
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/* Update global variables too */
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RecentGlobalXmin = globalxmin;
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RecentXmin = xmin;
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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 1.78 2004/09/13 20:07:36 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/utils/time/tqual.c,v 1.79 2004/09/16 18:35:22 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -48,6 +48,7 @@ Snapshot LatestSnapshot = NULL;
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Snapshot ActiveSnapshot = NULL;
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/* These are updated by GetSnapshotData: */
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TransactionId TransactionXmin = InvalidTransactionId;
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TransactionId RecentXmin = InvalidTransactionId;
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TransactionId RecentGlobalXmin = InvalidTransactionId;
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@ -8,7 +8,7 @@
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* Portions Copyright (c) 1996-2004, 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/utils/tqual.h,v 1.52 2004/09/13 20:08:35 tgl Exp $
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* $PostgreSQL: pgsql/src/include/utils/tqual.h,v 1.53 2004/09/16 18:35:23 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -59,6 +59,7 @@ extern DLLIMPORT Snapshot SerializableSnapshot;
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extern DLLIMPORT Snapshot LatestSnapshot;
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extern DLLIMPORT Snapshot ActiveSnapshot;
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extern TransactionId TransactionXmin;
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extern TransactionId RecentXmin;
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extern TransactionId RecentGlobalXmin;
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