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RecentXmin is too recent to use as the cutoff point for accessing

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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 2004-09-16 18:35:23 +00:00
parent 8f9f198603
commit 86fff990b2
5 changed files with 41 additions and 27 deletions
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14
src/backend/access/transam/subtrans.c
View File

@ -22,7 +22,7 @@
* Portions Copyright (c) 1996-2004, PostgreSQL Global Development Group * Portions Copyright (c) 1996-2004, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California * Portions Copyright (c) 1994, Regents of the University of California
* *
* $PostgreSQL: pgsql/src/backend/access/transam/subtrans.c,v 1.5 2004/08/29 05:06:40 momjian Exp $ * $PostgreSQL: pgsql/src/backend/access/transam/subtrans.c,v 1.6 2004/09/16 18:35:20 tgl Exp $
* *
*------------------------------------------------------------------------- *-------------------------------------------------------------------------
*/ */
@ -105,7 +105,7 @@ SubTransGetParent(TransactionId xid)
TransactionId parent; TransactionId parent;
/* Can't ask about stuff that might not be around anymore */ /* Can't ask about stuff that might not be around anymore */
Assert(TransactionIdFollowsOrEquals(xid, RecentXmin)); Assert(TransactionIdFollowsOrEquals(xid, TransactionXmin));
/* Bootstrap and frozen XIDs have no parent */ /* Bootstrap and frozen XIDs have no parent */
if (!TransactionIdIsNormal(xid)) if (!TransactionIdIsNormal(xid))
@ -129,12 +129,12 @@ SubTransGetParent(TransactionId xid)
* *
* Returns the topmost transaction of the given transaction id. * Returns the topmost transaction of the given transaction id.
* *
* Because we cannot look back further than RecentXmin, it is possible * Because we cannot look back further than TransactionXmin, it is possible
* that this function will lie and return an intermediate subtransaction ID * that this function will lie and return an intermediate subtransaction ID
* instead of the true topmost parent ID. This is OK, because in practice * instead of the true topmost parent ID. This is OK, because in practice
* we only care about detecting whether the topmost parent is still running * we only care about detecting whether the topmost parent is still running
* or is part of a current snapshot's list of still-running transactions. * or is part of a current snapshot's list of still-running transactions.
* Therefore, any XID before RecentXmin is as good as any other. * Therefore, any XID before TransactionXmin is as good as any other.
*/ */
TransactionId TransactionId
SubTransGetTopmostTransaction(TransactionId xid) SubTransGetTopmostTransaction(TransactionId xid)
@ -143,12 +143,12 @@ SubTransGetTopmostTransaction(TransactionId xid)
previousXid = xid; previousXid = xid;
/* Can't ask about stuff that might not be around anymore */ /* Can't ask about stuff that might not be around anymore */
Assert(TransactionIdFollowsOrEquals(xid, RecentXmin)); Assert(TransactionIdFollowsOrEquals(xid, TransactionXmin));
while (TransactionIdIsValid(parentXid)) while (TransactionIdIsValid(parentXid))
{ {
previousXid = parentXid; previousXid = parentXid;
if (TransactionIdPrecedes(parentXid, RecentXmin)) if (TransactionIdPrecedes(parentXid, TransactionXmin))
break; break;
parentXid = SubTransGetParent(parentXid); parentXid = SubTransGetParent(parentXid);
} }
@ -312,7 +312,7 @@ ExtendSUBTRANS(TransactionId newestXact)
* Remove all SUBTRANS segments before the one holding the passed transaction ID * Remove all SUBTRANS segments before the one holding the passed transaction ID
* *
* This is normally called during checkpoint, with oldestXact being the * This is normally called during checkpoint, with oldestXact being the
* oldest XMIN of any running transaction. * oldest TransactionXmin of any running transaction.
*/ */
void void
TruncateSUBTRANS(TransactionId oldestXact) TruncateSUBTRANS(TransactionId oldestXact)

14
src/backend/access/transam/transam.c
View File

@ -8,7 +8,7 @@
* *
* *
* IDENTIFICATION * IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/access/transam/transam.c,v 1.61 2004/08/29 05:06:40 momjian Exp $ * $PostgreSQL: pgsql/src/backend/access/transam/transam.c,v 1.62 2004/09/16 18:35:20 tgl Exp $
* *
* NOTES * NOTES
* This file contains the high level access-method interface to the * This file contains the high level access-method interface to the
@ -200,15 +200,15 @@ TransactionIdDidCommit(TransactionId transactionId)
/* /*
* If it's marked subcommitted, we have to check the parent * If it's marked subcommitted, we have to check the parent
* recursively. However, if it's older than RecentXmin, we can't look * recursively. However, if it's older than TransactionXmin, we can't
* at pg_subtrans; instead assume that the parent crashed without * look at pg_subtrans; instead assume that the parent crashed without
* cleaning up its children. * cleaning up its children.
*/ */
if (xidstatus == TRANSACTION_STATUS_SUB_COMMITTED) if (xidstatus == TRANSACTION_STATUS_SUB_COMMITTED)
{ {
TransactionId parentXid; TransactionId parentXid;
if (TransactionIdPrecedes(transactionId, RecentXmin)) if (TransactionIdPrecedes(transactionId, TransactionXmin))
return false; return false;
parentXid = SubTransGetParent(transactionId); parentXid = SubTransGetParent(transactionId);
Assert(TransactionIdIsValid(parentXid)); Assert(TransactionIdIsValid(parentXid));
@ -249,15 +249,15 @@ TransactionIdDidAbort(TransactionId transactionId)
/* /*
* If it's marked subcommitted, we have to check the parent * If it's marked subcommitted, we have to check the parent
* recursively. However, if it's older than RecentXmin, we can't look * recursively. However, if it's older than TransactionXmin, we can't
* at pg_subtrans; instead assume that the parent crashed without * look at pg_subtrans; instead assume that the parent crashed without
* cleaning up its children. * cleaning up its children.
*/ */
if (xidstatus == TRANSACTION_STATUS_SUB_COMMITTED) if (xidstatus == TRANSACTION_STATUS_SUB_COMMITTED)
{ {
TransactionId parentXid; TransactionId parentXid;
if (TransactionIdPrecedes(transactionId, RecentXmin)) if (TransactionIdPrecedes(transactionId, TransactionXmin))
return true; return true;
parentXid = SubTransGetParent(transactionId); parentXid = SubTransGetParent(transactionId);
Assert(TransactionIdIsValid(parentXid)); Assert(TransactionIdIsValid(parentXid));

34
src/backend/storage/ipc/sinval.c
View File

@ -8,7 +8,7 @@
* *
* *
* IDENTIFICATION * IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/storage/ipc/sinval.c,v 1.73 2004/09/06 23:33:35 tgl Exp $ * $PostgreSQL: pgsql/src/backend/storage/ipc/sinval.c,v 1.74 2004/09/16 18:35:21 tgl Exp $
* *
*------------------------------------------------------------------------- *-------------------------------------------------------------------------
*/ */
@ -521,7 +521,8 @@ TransactionIdIsInProgress(TransactionId xid)
bool locked; bool locked;
/* /*
* Don't bother checking a very old transaction. * Don't bother checking a transaction older than RecentXmin; it
* could not possibly still be running.
*/ */
if (TransactionIdPrecedes(xid, RecentXmin)) if (TransactionIdPrecedes(xid, RecentXmin))
{ {
@ -732,10 +733,19 @@ GetOldestXmin(bool allDbs)
* This ensures that the set of transactions seen as "running" by the * This ensures that the set of transactions seen as "running" by the
* current xact will not change after it takes the snapshot. * current xact will not change after it takes the snapshot.
* *
* We also compute the current global xmin (oldest xmin across all running * Note that only top-level XIDs are included in the snapshot. We can
* transactions) and save it in RecentGlobalXmin. This is the same * still apply the xmin and xmax limits to subtransaction XIDs, but we
* computation done by GetOldestXmin(TRUE). The xmin value is also stored * need to work a bit harder to see if XIDs in [xmin..xmax) are running.
* into RecentXmin. *
* We also update the following backend-global variables:
* TransactionXmin: the oldest xmin of any snapshot in use in the
* current transaction (this is the same as MyProc->xmin). This
* is just the xmin computed for the first, serializable snapshot.
* RecentXmin: the xmin computed for the most recent snapshot. XIDs
* older than this are known not running any more.
* RecentGlobalXmin: the global xmin (oldest TransactionXmin across all
* running transactions). This is the same computation done by
* GetOldestXmin(TRUE).
*---------- *----------
*/ */
Snapshot Snapshot
@ -751,6 +761,11 @@ GetSnapshotData(Snapshot snapshot, bool serializable)
Assert(snapshot != NULL); Assert(snapshot != NULL);
/* Serializable snapshot must be computed before any other... */
Assert(serializable ?
!TransactionIdIsValid(MyProc->xmin) :
TransactionIdIsValid(MyProc->xmin));
/* /*
* Allocating space for MaxBackends xids is usually overkill; * Allocating space for MaxBackends xids is usually overkill;
* lastBackend would be sufficient. But it seems better to do the * lastBackend would be sufficient. But it seems better to do the
@ -850,13 +865,10 @@ GetSnapshotData(Snapshot snapshot, bool serializable)
} }
if (serializable) if (serializable)
MyProc->xmin = xmin; MyProc->xmin = TransactionXmin = xmin;
LWLockRelease(SInvalLock); LWLockRelease(SInvalLock);
/* Serializable snapshot must be computed before any other... */
Assert(TransactionIdIsValid(MyProc->xmin));
/* /*
* Update globalxmin to include actual process xids. This is a * Update globalxmin to include actual process xids. This is a
* slightly different way of computing it than GetOldestXmin uses, but * slightly different way of computing it than GetOldestXmin uses, but
@ -865,7 +877,7 @@ GetSnapshotData(Snapshot snapshot, bool serializable)
if (TransactionIdPrecedes(xmin, globalxmin)) if (TransactionIdPrecedes(xmin, globalxmin))
globalxmin = xmin; globalxmin = xmin;
/* Update globals for use by VACUUM */ /* Update global variables too */
RecentGlobalXmin = globalxmin; RecentGlobalXmin = globalxmin;
RecentXmin = xmin; RecentXmin = xmin;

3
src/backend/utils/time/tqual.c
View File

@ -16,7 +16,7 @@
* Portions Copyright (c) 1994, Regents of the University of California * Portions Copyright (c) 1994, Regents of the University of California
* *
* IDENTIFICATION * IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/utils/time/tqual.c,v 1.78 2004/09/13 20:07:36 tgl Exp $ * $PostgreSQL: pgsql/src/backend/utils/time/tqual.c,v 1.79 2004/09/16 18:35:22 tgl Exp $
* *
*------------------------------------------------------------------------- *-------------------------------------------------------------------------
*/ */
@ -48,6 +48,7 @@ Snapshot LatestSnapshot = NULL;
Snapshot ActiveSnapshot = NULL; Snapshot ActiveSnapshot = NULL;
/* These are updated by GetSnapshotData: */ /* These are updated by GetSnapshotData: */
TransactionId TransactionXmin = InvalidTransactionId;
TransactionId RecentXmin = InvalidTransactionId; TransactionId RecentXmin = InvalidTransactionId;
TransactionId RecentGlobalXmin = InvalidTransactionId; TransactionId RecentGlobalXmin = InvalidTransactionId;

3
src/include/utils/tqual.h
View File

@ -8,7 +8,7 @@
* Portions Copyright (c) 1996-2004, PostgreSQL Global Development Group * Portions Copyright (c) 1996-2004, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California * Portions Copyright (c) 1994, Regents of the University of California
* *
* $PostgreSQL: pgsql/src/include/utils/tqual.h,v 1.52 2004/09/13 20:08:35 tgl Exp $ * $PostgreSQL: pgsql/src/include/utils/tqual.h,v 1.53 2004/09/16 18:35:23 tgl Exp $
* *
*------------------------------------------------------------------------- *-------------------------------------------------------------------------
*/ */
@ -59,6 +59,7 @@ extern DLLIMPORT Snapshot SerializableSnapshot;
extern DLLIMPORT Snapshot LatestSnapshot; extern DLLIMPORT Snapshot LatestSnapshot;
extern DLLIMPORT Snapshot ActiveSnapshot; extern DLLIMPORT Snapshot ActiveSnapshot;
extern TransactionId TransactionXmin;
extern TransactionId RecentXmin; extern TransactionId RecentXmin;
extern TransactionId RecentGlobalXmin; extern TransactionId RecentGlobalXmin;