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Commit32846f8

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Fix TransactionIdIsCurrentTransactionId() to use binary search instead of
linear search when checking child-transaction XIDs. This makes for animportant speedup in transactions that have large numbers of children,as in a recent example from Craig Ringer. We can also get rid of anugly kluge that represented lists of TransactionIds as lists of OIDs.Heikki Linnakangas
1 parenta7c58ab commit32846f8

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3 files changed

+128
-72
lines changed

3 files changed

+128
-72
lines changed

‎src/backend/access/transam/twophase.c

Lines changed: 1 addition & 2 deletions
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 1.39 2008/01/01 19:45:48 momjian Exp $
10+
*$PostgreSQL: pgsql/src/backend/access/transam/twophase.c,v 1.40 2008/03/17 02:18:55 tgl Exp $
1111
*
1212
* NOTES
1313
*Each global transaction is associated with a global transaction
@@ -827,7 +827,6 @@ StartPrepare(GlobalTransaction gxact)
827827
save_state_data(children,hdr.nsubxacts*sizeof(TransactionId));
828828
/* While we have the child-xact data, stuff it in the gxact too */
829829
GXactLoadSubxactData(gxact,hdr.nsubxacts,children);
830-
pfree(children);
831830
}
832831
if (hdr.ncommitrels>0)
833832
{

‎src/backend/access/transam/xact.c

Lines changed: 126 additions & 58 deletions
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 1.258 2008/03/04 19:54:06 tgl Exp $
13+
* $PostgreSQL: pgsql/src/backend/access/transam/xact.c,v 1.259 2008/03/17 02:18:55 tgl Exp $
1414
*
1515
*-------------------------------------------------------------------------
1616
*/
@@ -130,7 +130,9 @@ typedef struct TransactionStateData
130130
intgucNestLevel;/* GUC context nesting depth */
131131
MemoryContextcurTransactionContext;/* my xact-lifetime context */
132132
ResourceOwnercurTransactionOwner;/* my query resources */
133-
List*childXids;/* subcommitted child XIDs */
133+
TransactionId*childXids;/* subcommitted child XIDs, in XID order */
134+
intnChildXids;/* # of subcommitted child XIDs */
135+
intmaxChildXids;/* allocated size of childXids[] */
134136
OidprevUser;/* previous CurrentUserId setting */
135137
boolprevSecDefCxt;/* previous SecurityDefinerContext setting */
136138
boolprevXactReadOnly;/* entry-time xact r/o state */
@@ -156,7 +158,9 @@ static TransactionStateData TopTransactionStateData = {
156158
0,/* GUC context nesting depth */
157159
NULL,/* cur transaction context */
158160
NULL,/* cur transaction resource owner */
159-
NIL,/* subcommitted child Xids */
161+
NULL,/* subcommitted child Xids */
162+
0,/* # of subcommitted child Xids */
163+
0,/* allocated size of childXids[] */
160164
InvalidOid,/* previous CurrentUserId setting */
161165
false,/* previous SecurityDefinerContext setting */
162166
false,/* entry-time xact r/o state */
@@ -559,18 +563,30 @@ TransactionIdIsCurrentTransactionId(TransactionId xid)
559563
*/
560564
for (s=CurrentTransactionState;s!=NULL;s=s->parent)
561565
{
562-
ListCell*cell;
566+
intlow,high;
563567

564568
if (s->state==TRANS_ABORT)
565569
continue;
566570
if (!TransactionIdIsValid(s->transactionId))
567571
continue;/* it can't have any child XIDs either */
568572
if (TransactionIdEquals(xid,s->transactionId))
569573
return true;
570-
foreach(cell,s->childXids)
574+
/* As the childXids array is ordered, we can use binary search */
575+
low=0;
576+
high=s->nChildXids-1;
577+
while (low <=high)
571578
{
572-
if (TransactionIdEquals(xid,lfirst_xid(cell)))
579+
intmiddle;
580+
TransactionIdprobe;
581+
582+
middle=low+ (high-low) /2;
583+
probe=s->childXids[middle];
584+
if (TransactionIdEquals(probe,xid))
573585
return true;
586+
elseif (TransactionIdPrecedes(probe,xid))
587+
low=middle+1;
588+
else
589+
high=middle-1;
574590
}
575591
}
576592

@@ -985,8 +1001,6 @@ RecordTransactionCommit(void)
9851001
/* Clean up local data */
9861002
if (rels)
9871003
pfree(rels);
988-
if (children)
989-
pfree(children);
9901004

9911005
returnlatestXid;
9921006
}
@@ -1067,34 +1081,79 @@ static void
10671081
AtSubCommit_childXids(void)
10681082
{
10691083
TransactionStates=CurrentTransactionState;
1070-
MemoryContextold_cxt;
1084+
intnew_nChildXids;
10711085

10721086
Assert(s->parent!=NULL);
10731087

10741088
/*
1075-
* We keep the child-XID lists in TopTransactionContext; this avoids
1076-
* setting up child-transaction contexts for what might be just a few
1077-
* bytes of grandchild XIDs.
1089+
* The parent childXids array will need to hold my XID and all my
1090+
* childXids, in addition to the XIDs already there.
10781091
*/
1079-
old_cxt=MemoryContextSwitchTo(TopTransactionContext);
1080-
1081-
s->parent->childXids=lappend_xid(s->parent->childXids,
1082-
s->transactionId);
1092+
new_nChildXids=s->parent->nChildXids+s->nChildXids+1;
10831093

1084-
if (s->childXids!=NIL)
1094+
/* Allocate or enlarge the parent array if necessary */
1095+
if (s->parent->maxChildXids<new_nChildXids)
10851096
{
1086-
s->parent->childXids=list_concat(s->parent->childXids,
1087-
s->childXids);
1097+
intnew_maxChildXids;
1098+
TransactionId*new_childXids;
10881099

10891100
/*
1090-
* list_concat doesn't free the list header for the second list; do so
1091-
* here to avoid memory leakage (kluge)
1101+
* Make it 2x what's needed right now, to avoid having to enlarge it
1102+
* repeatedly. But we can't go above MaxAllocSize. (The latter
1103+
* limit is what ensures that we don't need to worry about integer
1104+
* overflow here or in the calculation of new_nChildXids.)
10921105
*/
1093-
pfree(s->childXids);
1094-
s->childXids=NIL;
1106+
new_maxChildXids=Min(new_nChildXids*2,
1107+
(int) (MaxAllocSize /sizeof(TransactionId)));
1108+
1109+
if (new_maxChildXids<new_nChildXids)
1110+
ereport(ERROR,
1111+
(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
1112+
errmsg("maximum number of committed subtransactions (%d) exceeded",
1113+
(int) (MaxAllocSize /sizeof(TransactionId)))));
1114+
1115+
/*
1116+
* We keep the child-XID arrays in TopTransactionContext; this avoids
1117+
* setting up child-transaction contexts for what might be just a few
1118+
* bytes of grandchild XIDs.
1119+
*/
1120+
if (s->parent->childXids==NULL)
1121+
new_childXids=
1122+
MemoryContextAlloc(TopTransactionContext,
1123+
new_maxChildXids*sizeof(TransactionId));
1124+
else
1125+
new_childXids=repalloc(s->parent->childXids,
1126+
new_maxChildXids*sizeof(TransactionId));
1127+
1128+
s->parent->childXids=new_childXids;
1129+
s->parent->maxChildXids=new_maxChildXids;
10951130
}
10961131

1097-
MemoryContextSwitchTo(old_cxt);
1132+
/*
1133+
* Copy all my XIDs to parent's array.
1134+
*
1135+
* Note: We rely on the fact that the XID of a child always follows that
1136+
* of its parent. By copying the XID of this subtransaction before the
1137+
* XIDs of its children, we ensure that the array stays ordered. Likewise,
1138+
* all XIDs already in the array belong to subtransactions started and
1139+
* subcommitted before us, so their XIDs must precede ours.
1140+
*/
1141+
s->parent->childXids[s->parent->nChildXids]=s->transactionId;
1142+
1143+
if (s->nChildXids>0)
1144+
memcpy(&s->parent->childXids[s->parent->nChildXids+1],
1145+
s->childXids,
1146+
s->nChildXids*sizeof(TransactionId));
1147+
1148+
s->parent->nChildXids=new_nChildXids;
1149+
1150+
/* Release child's array to avoid leakage */
1151+
if (s->childXids!=NULL)
1152+
pfree(s->childXids);
1153+
/* We must reset these to avoid double-free if fail later in commit */
1154+
s->childXids=NULL;
1155+
s->nChildXids=0;
1156+
s->maxChildXids=0;
10981157
}
10991158

11001159
/*
@@ -1259,8 +1318,6 @@ RecordTransactionAbort(bool isSubXact)
12591318
/* And clean up local data */
12601319
if (rels)
12611320
pfree(rels);
1262-
if (children)
1263-
pfree(children);
12641321

12651322
returnlatestXid;
12661323
}
@@ -1332,12 +1389,15 @@ AtSubAbort_childXids(void)
13321389
TransactionStates=CurrentTransactionState;
13331390

13341391
/*
1335-
* We keep the child-XIDlists in TopTransactionContext (see
1336-
* AtSubCommit_childXids).This means we'd better free thelist
1392+
* We keep the child-XIDarrays in TopTransactionContext (see
1393+
* AtSubCommit_childXids).This means we'd better free thearray
13371394
* explicitly at abort to avoid leakage.
13381395
*/
1339-
list_free(s->childXids);
1340-
s->childXids=NIL;
1396+
if (s->childXids!=NULL)
1397+
pfree(s->childXids);
1398+
s->childXids=NULL;
1399+
s->nChildXids=0;
1400+
s->maxChildXids=0;
13411401
}
13421402

13431403
/* ----------------------------------------------------------------
@@ -1506,7 +1566,9 @@ StartTransaction(void)
15061566
*/
15071567
s->nestingLevel=1;
15081568
s->gucNestLevel=1;
1509-
s->childXids=NIL;
1569+
s->childXids=NULL;
1570+
s->nChildXids=0;
1571+
s->maxChildXids=0;
15101572
GetUserIdAndContext(&s->prevUser,&s->prevSecDefCxt);
15111573
/* SecurityDefinerContext should never be set outside a transaction */
15121574
Assert(!s->prevSecDefCxt);
@@ -1702,7 +1764,9 @@ CommitTransaction(void)
17021764
s->subTransactionId=InvalidSubTransactionId;
17031765
s->nestingLevel=0;
17041766
s->gucNestLevel=0;
1705-
s->childXids=NIL;
1767+
s->childXids=NULL;
1768+
s->nChildXids=0;
1769+
s->maxChildXids=0;
17061770

17071771
/*
17081772
* done with commit processing, set current transaction state back to
@@ -1931,7 +1995,9 @@ PrepareTransaction(void)
19311995
s->subTransactionId=InvalidSubTransactionId;
19321996
s->nestingLevel=0;
19331997
s->gucNestLevel=0;
1934-
s->childXids=NIL;
1998+
s->childXids=NULL;
1999+
s->nChildXids=0;
2000+
s->maxChildXids=0;
19352001

19362002
/*
19372003
* done with 1st phase commit processing, set current transaction state
@@ -2101,7 +2167,9 @@ CleanupTransaction(void)
21012167
s->subTransactionId=InvalidSubTransactionId;
21022168
s->nestingLevel=0;
21032169
s->gucNestLevel=0;
2104-
s->childXids=NIL;
2170+
s->childXids=NULL;
2171+
s->nChildXids=0;
2172+
s->maxChildXids=0;
21052173

21062174
/*
21072175
* done with abort processing, set current transaction state back to
@@ -4051,6 +4119,19 @@ ShowTransactionState(const char *str)
40514119
staticvoid
40524120
ShowTransactionStateRec(TransactionStates)
40534121
{
4122+
StringInfoDatabuf;
4123+
4124+
initStringInfo(&buf);
4125+
4126+
if (s->nChildXids>0)
4127+
{
4128+
inti;
4129+
4130+
appendStringInfo(&buf,"%u",s->childXids[0]);
4131+
for (i=1;i<s->nChildXids;i++)
4132+
appendStringInfo(&buf," %u",s->childXids[i]);
4133+
}
4134+
40544135
if (s->parent)
40554136
ShowTransactionStateRec(s->parent);
40564137

@@ -4064,8 +4145,9 @@ ShowTransactionStateRec(TransactionState s)
40644145
(unsignedint)s->subTransactionId,
40654146
(unsignedint)currentCommandId,
40664147
currentCommandIdUsed ?" (used)" :"",
4067-
s->nestingLevel,
4068-
nodeToString(s->childXids))));
4148+
s->nestingLevel,buf.data)));
4149+
4150+
pfree(buf.data);
40694151
}
40704152

40714153
/*
@@ -4144,36 +4226,22 @@ TransStateAsString(TransState state)
41444226
* xactGetCommittedChildren
41454227
*
41464228
* Gets the list of committed children of the current transaction.The return
4147-
* value is the number of child transactions. *children is set to point to a
4148-
* palloc'd array of TransactionIds. If there are no subxacts, *children is
4149-
* set to NULL.
4229+
* value is the number of child transactions. *ptr is set to point to an
4230+
* array of TransactionIds. The array is allocated in TopTransactionContext;
4231+
* the caller should *not* pfree() it (this is a change from pre-8.4 code!).
4232+
* If there are no subxacts, *ptr is set to NULL.
41504233
*/
41514234
int
41524235
xactGetCommittedChildren(TransactionId**ptr)
41534236
{
41544237
TransactionStates=CurrentTransactionState;
4155-
intnchildren;
4156-
TransactionId*children;
4157-
ListCell*p;
41584238

4159-
nchildren=list_length(s->childXids);
4160-
if (nchildren==0)
4161-
{
4239+
if (s->nChildXids==0)
41624240
*ptr=NULL;
4163-
return0;
4164-
}
4165-
4166-
children= (TransactionId*)palloc(nchildren*sizeof(TransactionId));
4167-
*ptr=children;
4168-
4169-
foreach(p,s->childXids)
4170-
{
4171-
TransactionIdchild=lfirst_xid(p);
4172-
4173-
*children++=child;
4174-
}
4241+
else
4242+
*ptr=s->childXids;
41754243

4176-
returnnchildren;
4244+
returns->nChildXids;
41774245
}
41784246

41794247
/*

‎src/include/nodes/pg_list.h

Lines changed: 1 addition & 12 deletions
Original file line numberDiff line numberDiff line change
@@ -26,16 +26,11 @@
2626
* (At the moment, ints and Oids are the same size, but they may not
2727
* always be so; try to be careful to maintain the distinction.)
2828
*
29-
* There is also limited support for lists of TransactionIds; since these
30-
* are used in only one or two places, we don't provide a full implementation,
31-
* but map them onto Oid lists. This effectively assumes that TransactionId
32-
* is no wider than Oid and both are unsigned types.
33-
*
3429
*
3530
* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
3631
* Portions Copyright (c) 1994, Regents of the University of California
3732
*
38-
* $PostgreSQL: pgsql/src/include/nodes/pg_list.h,v 1.57 2008/01/01 19:45:58 momjian Exp $
33+
* $PostgreSQL: pgsql/src/include/nodes/pg_list.h,v 1.58 2008/03/17 02:18:55 tgl Exp $
3934
*
4035
*-------------------------------------------------------------------------
4136
*/
@@ -159,12 +154,6 @@ extern intlist_length(List *l);
159154
#definelist_make3_oid(x1,x2,x3)lcons_oid(x1, list_make2_oid(x2, x3))
160155
#definelist_make4_oid(x1,x2,x3,x4) lcons_oid(x1, list_make3_oid(x2, x3, x4))
161156

162-
/*
163-
* Limited support for lists of TransactionIds, mapped onto lists of Oids
164-
*/
165-
#definelfirst_xid(lc)((TransactionId) lfirst_oid(lc))
166-
#definelappend_xid(list,datum)lappend_oid(list, (Oid) (datum))
167-
168157
/*
169158
* foreach -
170159
* a convenience macro which loops through the list

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