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Commit92c2ecc

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Modify snapshot definition so that lazy vacuums are ignored by other
vacuums. This allows a OLTP-like system with big tables to continueregular vacuuming on small-but-frequently-updated tables while thebig tables are being vacuumed.Original patch from Hannu Krossing, rewritten by Tom Lane and updatedby me.
1 parentd660379 commit92c2ecc

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9 files changed

+99
-28
lines changed

9 files changed

+99
-28
lines changed

‎src/backend/access/transam/twophase.c‎

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
77
* Portions Copyright (c) 1994, Regents of the University of California
88
*
99
* IDENTIFICATION
10-
*$PostgreSQL: pgsql/src/backend/access/transam/twophase.c,v 1.21 2006/07/14 14:52:17 momjian Exp $
10+
*$PostgreSQL: pgsql/src/backend/access/transam/twophase.c,v 1.22 2006/07/30 02:07:18 alvherre Exp $
1111
*
1212
* NOTES
1313
*Each global transaction is associated with a global transaction
@@ -279,6 +279,7 @@ MarkAsPreparing(TransactionId xid, const char *gid,
279279
gxact->proc.pid=0;
280280
gxact->proc.databaseId=databaseid;
281281
gxact->proc.roleId=owner;
282+
gxact->proc.inVacuum= false;
282283
gxact->proc.lwWaiting= false;
283284
gxact->proc.lwExclusive= false;
284285
gxact->proc.lwWaitLink=NULL;

‎src/backend/access/transam/xact.c‎

Lines changed: 4 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -10,7 +10,7 @@
1010
*
1111
*
1212
* IDENTIFICATION
13-
* $PostgreSQL: pgsql/src/backend/access/transam/xact.c,v 1.224 2006/07/24 16:32:44 petere Exp $
13+
* $PostgreSQL: pgsql/src/backend/access/transam/xact.c,v 1.225 2006/07/30 02:07:18 alvherre Exp $
1414
*
1515
*-------------------------------------------------------------------------
1616
*/
@@ -1529,6 +1529,7 @@ CommitTransaction(void)
15291529
LWLockAcquire(ProcArrayLock,LW_EXCLUSIVE);
15301530
MyProc->xid=InvalidTransactionId;
15311531
MyProc->xmin=InvalidTransactionId;
1532+
MyProc->inVacuum= false;/* must be cleared with xid/xmin */
15321533

15331534
/* Clear the subtransaction-XID cache too while holding the lock */
15341535
MyProc->subxids.nxids=0;
@@ -1764,6 +1765,7 @@ PrepareTransaction(void)
17641765
LWLockAcquire(ProcArrayLock,LW_EXCLUSIVE);
17651766
MyProc->xid=InvalidTransactionId;
17661767
MyProc->xmin=InvalidTransactionId;
1768+
MyProc->inVacuum= false;/* must be cleared with xid/xmin */
17671769

17681770
/* Clear the subtransaction-XID cache too while holding the lock */
17691771
MyProc->subxids.nxids=0;
@@ -1927,6 +1929,7 @@ AbortTransaction(void)
19271929
LWLockAcquire(ProcArrayLock,LW_EXCLUSIVE);
19281930
MyProc->xid=InvalidTransactionId;
19291931
MyProc->xmin=InvalidTransactionId;
1932+
MyProc->inVacuum= false;/* must be cleared with xid/xmin */
19301933

19311934
/* Clear the subtransaction-XID cache too while holding the lock */
19321935
MyProc->subxids.nxids=0;

‎src/backend/access/transam/xlog.c‎

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
77
* Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
88
* Portions Copyright (c) 1994, Regents of the University of California
99
*
10-
* $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.244 2006/07/14 14:52:17 momjian Exp $
10+
* $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.245 2006/07/30 02:07:18 alvherre Exp $
1111
*
1212
*-------------------------------------------------------------------------
1313
*/
@@ -5413,7 +5413,7 @@ CreateCheckPoint(bool shutdown, bool force)
54135413
* StartupSUBTRANS hasn't been called yet.
54145414
*/
54155415
if (!InRecovery)
5416-
TruncateSUBTRANS(GetOldestXmin(true));
5416+
TruncateSUBTRANS(GetOldestXmin(true, false));
54175417

54185418
if (!shutdown)
54195419
ereport(DEBUG2,

‎src/backend/catalog/index.c‎

Lines changed: 3 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/backend/catalog/index.c,v 1.269 2006/07/13 16:49:13 momjian Exp $
11+
* $PostgreSQL: pgsql/src/backend/catalog/index.c,v 1.270 2006/07/30 02:07:18 alvherre Exp $
1212
*
1313
*
1414
* INTERFACE ROUTINES
@@ -1367,7 +1367,8 @@ IndexBuildHeapScan(Relation heapRelation,
13671367
else
13681368
{
13691369
snapshot=SnapshotAny;
1370-
OldestXmin=GetOldestXmin(heapRelation->rd_rel->relisshared);
1370+
/* okay to ignore lazy VACUUMs here */
1371+
OldestXmin=GetOldestXmin(heapRelation->rd_rel->relisshared, true);
13711372
}
13721373

13731374
scan=heap_beginscan(heapRelation,/* relation */

‎src/backend/commands/vacuum.c‎

Lines changed: 46 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -13,7 +13,7 @@
1313
*
1414
*
1515
* IDENTIFICATION
16-
* $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.335 2006/07/14 14:52:18momjian Exp $
16+
* $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.336 2006/07/30 02:07:18alvherre Exp $
1717
*
1818
*-------------------------------------------------------------------------
1919
*/
@@ -37,6 +37,7 @@
3737
#include"postmaster/autovacuum.h"
3838
#include"storage/freespace.h"
3939
#include"storage/pmsignal.h"
40+
#include"storage/proc.h"
4041
#include"storage/procarray.h"
4142
#include"utils/acl.h"
4243
#include"utils/builtins.h"
@@ -589,7 +590,16 @@ vacuum_set_xid_limits(VacuumStmt *vacstmt, bool sharedRel,
589590
{
590591
TransactionIdlimit;
591592

592-
*oldestXmin=GetOldestXmin(sharedRel);
593+
/*
594+
* We can always ignore processes running lazy vacuum. This is because we
595+
* use these values only for deciding which tuples we must keep in the
596+
* tables. Since lazy vacuum doesn't write its xid to the table, it's
597+
* safe to ignore it. In theory it could be problematic to ignore lazy
598+
* vacuums on a full vacuum, but keep in mind that only one vacuum process
599+
* can be working on a particular table at any time, and that each vacuum
600+
* is always an independent transaction.
601+
*/
602+
*oldestXmin=GetOldestXmin(sharedRel, true);
593603

594604
Assert(TransactionIdIsNormal(*oldestXmin));
595605

@@ -645,6 +655,11 @@ vacuum_set_xid_limits(VacuumStmt *vacstmt, bool sharedRel,
645655
*pg_class would've been obsoleted. Of course, this only works for
646656
*fixed-size never-null columns, but these are.
647657
*
658+
*Another reason for doing it this way is that when we are in a lazy
659+
*VACUUM and have inVacuum set, we mustn't do any updates --- somebody
660+
*vacuuming pg_class might think they could delete a tuple marked with
661+
*xmin = our xid.
662+
*
648663
*This routine is shared by full VACUUM, lazy VACUUM, and stand-alone
649664
*ANALYZE.
650665
*/
@@ -996,8 +1011,35 @@ vacuum_rel(Oid relid, VacuumStmt *vacstmt, char expected_relkind)
9961011

9971012
/* Begin a transaction for vacuuming this relation */
9981013
StartTransactionCommand();
999-
/* functions in indexes may want a snapshot set */
1000-
ActiveSnapshot=CopySnapshot(GetTransactionSnapshot());
1014+
1015+
if (vacstmt->full)
1016+
{
1017+
/* functions in indexes may want a snapshot set */
1018+
ActiveSnapshot=CopySnapshot(GetTransactionSnapshot());
1019+
}
1020+
else
1021+
{
1022+
/*
1023+
* During a lazy VACUUM we do not run any user-supplied functions,
1024+
* and so it should be safe to not create a transaction snapshot.
1025+
*
1026+
* We can furthermore set the inVacuum flag, which lets other
1027+
* concurrent VACUUMs know that they can ignore this one while
1028+
* determining their OldestXmin. (The reason we don't set inVacuum
1029+
* during a full VACUUM is exactly that we may have to run user-
1030+
* defined functions for functional indexes, and we want to make
1031+
* sure that if they use the snapshot set above, any tuples it
1032+
* requires can't get removed from other tables. An index function
1033+
* that depends on the contents of other tables is arguably broken,
1034+
* but we won't break it here by violating transaction semantics.)
1035+
*
1036+
* Note: the inVacuum flag remains set until CommitTransaction or
1037+
* AbortTransaction. We don't want to clear it until we reset
1038+
* MyProc->xid/xmin, else OldestXmin might appear to go backwards,
1039+
* which is probably Not Good.
1040+
*/
1041+
MyProc->inVacuum= true;
1042+
}
10011043

10021044
/*
10031045
* Tell the cache replacement strategy that vacuum is causing all

‎src/backend/storage/ipc/procarray.c‎

Lines changed: 31 additions & 12 deletions
Original file line numberDiff line numberDiff line change
@@ -23,7 +23,7 @@
2323
*
2424
*
2525
* IDENTIFICATION
26-
* $PostgreSQL: pgsql/src/backend/storage/ipc/procarray.c,v 1.14 2006/07/14 14:52:22 momjian Exp $
26+
* $PostgreSQL: pgsql/src/backend/storage/ipc/procarray.c,v 1.15 2006/07/30 02:07:18 alvherre Exp $
2727
*
2828
*-------------------------------------------------------------------------
2929
*/
@@ -388,20 +388,24 @@ TransactionIdIsActive(TransactionId xid)
388388
* If allDbs is TRUE then all backends are considered; if allDbs is FALSE
389389
* then only backends running in my own database are considered.
390390
*
391+
* If ignoreVacuum is TRUE then backends with inVacuum set are ignored.
392+
*
391393
* This is used by VACUUM to decide which deleted tuples must be preserved
392394
* in a table.allDbs = TRUE is needed for shared relations, but allDbs =
393395
* FALSE is sufficient for non-shared relations, since only backends in my
394-
* own database could ever see the tuples in them.
396+
* own database could ever see the tuples in them. Also, we can ignore
397+
* concurrently running lazy VACUUMs because (a) they must be working on other
398+
* tables, and (b) they don't need to do snapshot-based lookups.
395399
*
396400
* This is also used to determine where to truncate pg_subtrans. allDbs
397-
* must be TRUE for that case.
401+
* must be TRUE for that case, and ignoreVacuum FALSE.
398402
*
399403
* Note: we include the currently running xids in the set of considered xids.
400404
* This ensures that if a just-started xact has not yet set its snapshot,
401405
* when it does set the snapshot it cannot set xmin less than what we compute.
402406
*/
403407
TransactionId
404-
GetOldestXmin(boolallDbs)
408+
GetOldestXmin(boolallDbs,boolignoreVacuum)
405409
{
406410
ProcArrayStruct*arrayP=procArray;
407411
TransactionIdresult;
@@ -425,15 +429,28 @@ GetOldestXmin(bool allDbs)
425429
{
426430
PGPROC*proc=arrayP->procs[index];
427431

432+
if (ignoreVacuum&&proc->inVacuum)
433+
continue;
434+
428435
if (allDbs||proc->databaseId==MyDatabaseId)
429436
{
430437
/* Fetch xid just once - see GetNewTransactionId */
431438
TransactionIdxid=proc->xid;
432439

433440
if (TransactionIdIsNormal(xid))
434441
{
442+
/* First consider the transaction own's Xid */
435443
if (TransactionIdPrecedes(xid,result))
436444
result=xid;
445+
446+
/*
447+
* Also consider the transaction's Xmin, if set.
448+
*
449+
* Note that this Xmin may seem to be guaranteed to be always
450+
* lower than the transaction's Xid, but this is not so because
451+
* there is a time window on which the Xid is already assigned
452+
* but the Xmin has not being calculated yet.
453+
*/
437454
xid=proc->xmin;
438455
if (TransactionIdIsNormal(xid))
439456
if (TransactionIdPrecedes(xid,result))
@@ -471,8 +488,8 @@ GetOldestXmin(bool allDbs)
471488
*RecentXmin: the xmin computed for the most recent snapshot. XIDs
472489
*older than this are known not running any more.
473490
*RecentGlobalXmin: the global xmin (oldest TransactionXmin across all
474-
*running transactions).This is the same computation done by
475-
*GetOldestXmin(TRUE).
491+
*running transactions, except those running LAZY VACUUM). This is
492+
*the same computation done byGetOldestXmin(true, false).
476493
*----------
477494
*/
478495
Snapshot
@@ -561,15 +578,17 @@ GetSnapshotData(Snapshot snapshot, bool serializable)
561578

562579
/*
563580
* Ignore my own proc (dealt with my xid above), procs not running a
564-
* transaction, and xacts started since we read the next transaction
565-
* ID.There's no need to store XIDs above what we got from
566-
* ReadNewTransactionId, since we'll treat them as running anyway. We
567-
* also assume that such xacts can't compute an xmin older than ours,
568-
* so they needn't be considered in computing globalxmin.
581+
* transaction, xacts started since we read the next transaction
582+
* ID, and xacts executing LAZY VACUUM.There's no need to store XIDs
583+
* above what we got from ReadNewTransactionId, since we'll treat them
584+
* as running anyway. We also assume that such xacts can't compute an
585+
* xmin older than ours, so they needn't be considered in computing
586+
* globalxmin.
569587
*/
570588
if (proc==MyProc||
571589
!TransactionIdIsNormal(xid)||
572-
TransactionIdFollowsOrEquals(xid,xmax))
590+
TransactionIdFollowsOrEquals(xid,xmax)||
591+
proc->inVacuum)
573592
continue;
574593

575594
if (TransactionIdPrecedes(xid,xmin))

‎src/backend/storage/lmgr/proc.c‎

Lines changed: 3 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/backend/storage/lmgr/proc.c,v 1.178 2006/07/23 23:08:46 tgl Exp $
11+
* $PostgreSQL: pgsql/src/backend/storage/lmgr/proc.c,v 1.179 2006/07/30 02:07:18 alvherre Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -257,6 +257,7 @@ InitProcess(void)
257257
/* databaseId and roleId will be filled in later */
258258
MyProc->databaseId=InvalidOid;
259259
MyProc->roleId=InvalidOid;
260+
MyProc->inVacuum= false;
260261
MyProc->lwWaiting= false;
261262
MyProc->lwExclusive= false;
262263
MyProc->lwWaitLink=NULL;
@@ -388,6 +389,7 @@ InitDummyProcess(void)
388389
MyProc->xmin=InvalidTransactionId;
389390
MyProc->databaseId=InvalidOid;
390391
MyProc->roleId=InvalidOid;
392+
MyProc->inVacuum= false;
391393
MyProc->lwWaiting= false;
392394
MyProc->lwExclusive= false;
393395
MyProc->lwWaitLink=NULL;

‎src/include/storage/proc.h‎

Lines changed: 6 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
77
* Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
88
* Portions Copyright (c) 1994, Regents of the University of California
99
*
10-
* $PostgreSQL: pgsql/src/include/storage/proc.h,v 1.89 2006/07/13 16:49:20 momjian Exp $
10+
* $PostgreSQL: pgsql/src/include/storage/proc.h,v 1.90 2006/07/30 02:07:18 alvherre Exp $
1111
*
1212
*-------------------------------------------------------------------------
1313
*/
@@ -66,13 +66,16 @@ struct PGPROC
6666
* this proc */
6767

6868
TransactionIdxmin;/* minimal running XID as it was when we were
69-
* starting our xact: vacuum must not remove
70-
* tuples deleted by xid >= xmin ! */
69+
* starting our xact, excluding LAZY VACUUM:
70+
* vacuum must not remove tuples deleted by
71+
* xid >= xmin ! */
7172

7273
intpid;/* This backend's process id, or 0 */
7374
OiddatabaseId;/* OID of database this backend is using */
7475
OidroleId;/* OID of role using this backend */
7576

77+
boolinVacuum;/* true if current xact is a LAZY VACUUM */
78+
7679
/* Info about LWLock the process is currently waiting for, if any. */
7780
boollwWaiting;/* true if waiting for an LW lock */
7881
boollwExclusive;/* true if waiting for exclusive access */

‎src/include/storage/procarray.h‎

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
77
* Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
88
* Portions Copyright (c) 1994, Regents of the University of California
99
*
10-
* $PostgreSQL: pgsql/src/include/storage/procarray.h,v 1.9 2006/06/19 01:51:22 tgl Exp $
10+
* $PostgreSQL: pgsql/src/include/storage/procarray.h,v 1.10 2006/07/30 02:07:18 alvherre Exp $
1111
*
1212
*-------------------------------------------------------------------------
1313
*/
@@ -24,7 +24,7 @@ extern void ProcArrayRemove(PGPROC *proc);
2424

2525
externboolTransactionIdIsInProgress(TransactionIdxid);
2626
externboolTransactionIdIsActive(TransactionIdxid);
27-
externTransactionIdGetOldestXmin(boolallDbs);
27+
externTransactionIdGetOldestXmin(boolallDbs,boolignoreVacuum);
2828

2929
externPGPROC*BackendPidGetProc(intpid);
3030
externintBackendXidGetPid(TransactionIdxid);

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