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Commit21d6a6a

Browse files
Tune GetSnapshotData() during Hot Standby by avoiding loop
through normal backends. Makes code clearer also, since weavoid various Assert()s. Performance of snapshots takenduring recovery no longer depends upon number of read-onlybackends.
1 parent7b130fb commit21d6a6a

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3 files changed

+79
-71
lines changed

3 files changed

+79
-71
lines changed

‎src/backend/access/transam/xlog.c‎

Lines changed: 7 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
77
* Portions Copyright (c) 1996-2010, 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 1.397 2010/04/16 08:58:16 heikki Exp $
10+
* $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.398 2010/04/18 18:05:51 sriggs Exp $
1111
*
1212
*-------------------------------------------------------------------------
1313
*/
@@ -6454,6 +6454,12 @@ CheckRecoveryConsistency(void)
64546454
}
64556455
}
64566456

6457+
bool
6458+
XLogConsistentState(void)
6459+
{
6460+
returnreachedMinRecoveryPoint;
6461+
}
6462+
64576463
/*
64586464
* Is the system still in recovery?
64596465
*

‎src/backend/storage/ipc/procarray.c‎

Lines changed: 70 additions & 69 deletions
Original file line numberDiff line numberDiff line change
@@ -37,7 +37,7 @@
3737
*
3838
*
3939
* IDENTIFICATION
40-
* $PostgreSQL: pgsql/src/backend/storage/ipc/procarray.c,v 1.62 2010/04/06 10:50:57 sriggs Exp $
40+
* $PostgreSQL: pgsql/src/backend/storage/ipc/procarray.c,v 1.63 2010/04/18 18:05:55 sriggs Exp $
4141
*
4242
*-------------------------------------------------------------------------
4343
*/
@@ -1091,89 +1091,90 @@ GetSnapshotData(Snapshot snapshot)
10911091
globalxmin=xmin=xmax;
10921092

10931093
/*
1094-
* Spin over procArray checking xid, xmin, and subxids. The goal is to
1095-
* gather all active xids, find the lowest xmin, and try to record
1096-
* subxids.
1094+
* If in recovery get any known assigned xids.
10971095
*/
1098-
for (index=0;index<arrayP->numProcs;index++)
1096+
if (!snapshot->takenDuringRecovery)
10991097
{
1100-
volatilePGPROC*proc=arrayP->procs[index];
1101-
TransactionIdxid;
1102-
1103-
/* Ignore procs running LAZY VACUUM */
1104-
if (proc->vacuumFlags&PROC_IN_VACUUM)
1105-
continue;
1106-
1107-
/* Update globalxmin to be the smallest valid xmin */
1108-
xid=proc->xmin;/* fetch just once */
1109-
if (TransactionIdIsNormal(xid)&&
1110-
TransactionIdPrecedes(xid,globalxmin))
1111-
globalxmin=xid;
1112-
1113-
/* Fetch xid just once - see GetNewTransactionId */
1114-
xid=proc->xid;
1115-
11161098
/*
1117-
* If the transaction has been assigned an xid < xmax we add it to the
1118-
* snapshot, and update xmin if necessary.There's no need to store
1119-
* XIDs >= xmax, since we'll treat them as running anyway. We don't
1120-
* bother to examine their subxids either.
1121-
*
1122-
* We don't include our own XID (if any) in the snapshot, but we must
1123-
* include it into xmin.
1099+
* Spin over procArray checking xid, xmin, and subxids. The goal is to
1100+
* gather all active xids, find the lowest xmin, and try to record
1101+
* subxids. During recovery no xids will be assigned, so all normal
1102+
* backends can be ignored, nor are there any VACUUMs running. All
1103+
* prepared transaction xids are held in KnownAssignedXids, so these
1104+
* will be seen without needing to loop through procs here.
11241105
*/
1125-
if (TransactionIdIsNormal(xid))
1106+
for (index=0;index<arrayP->numProcs;index++)
11261107
{
1127-
Assert(!snapshot->takenDuringRecovery);
1128-
if (TransactionIdFollowsOrEquals(xid,xmax))
1108+
volatilePGPROC*proc=arrayP->procs[index];
1109+
TransactionIdxid;
1110+
1111+
/* Ignore procs running LAZY VACUUM */
1112+
if (proc->vacuumFlags&PROC_IN_VACUUM)
11291113
continue;
1130-
if (proc!=MyProc)
1131-
snapshot->xip[count++]=xid;
1132-
if (TransactionIdPrecedes(xid,xmin))
1133-
xmin=xid;
1134-
}
11351114

1136-
/*
1137-
* Save subtransaction XIDs if possible (if we've already overflowed,
1138-
* there's no point). Note that the subxact XIDs must be later than
1139-
* their parent, so no need to check them against xmin. We could
1140-
* filter against xmax, but it seems better not to do that much work
1141-
* while holding the ProcArrayLock.
1142-
*
1143-
* The other backend can add more subxids concurrently, but cannot
1144-
* remove any.Hence it's important to fetch nxids just once. Should
1145-
* be safe to use memcpy, though. (We needn't worry about missing any
1146-
*xids added concurrently, because they must postdatexmax.)
1147-
*
1148-
*Again, our own XIDs are not included in the snapshot.
1149-
*/
1150-
if (!suboverflowed&&proc!=MyProc)
1151-
{
1152-
if (proc->subxids.overflowed)
1153-
suboverflowed= true;
1154-
else
1115+
/* Update globalxmin to be the smallest valid xmin */
1116+
xid=proc->xmin;/* fetch just once */
1117+
if (TransactionIdIsNormal(xid)&&
1118+
TransactionIdPrecedes(xid,globalxmin))
1119+
globalxmin=xid;
1120+
1121+
/* Fetch xid just once - see GetNewTransactionId */
1122+
xid=proc->xid;
1123+
1124+
/*
1125+
*If the transaction has been assigned an xid <xmax we add it to the
1126+
* snapshot, and update xmin if necessary.There's no need to store
1127+
*XIDs >= xmax, since we'll treat them as running anyway. We don't
1128+
* bother to examine their subxids either.
1129+
*
1130+
* We don't include our own XID (if any) in the snapshot, but we must
1131+
* include it into xmin.
1132+
*/
1133+
if (TransactionIdIsNormal(xid))
11551134
{
1156-
intnxids=proc->subxids.nxids;
1135+
if (TransactionIdFollowsOrEquals(xid,xmax))
1136+
continue;
1137+
if (proc!=MyProc)
1138+
snapshot->xip[count++]=xid;
1139+
if (TransactionIdPrecedes(xid,xmin))
1140+
xmin=xid;
1141+
}
11571142

1158-
if (nxids>0)
1143+
/*
1144+
* Save subtransaction XIDs if possible (if we've already overflowed,
1145+
* there's no point). Note that the subxact XIDs must be later than
1146+
* their parent, so no need to check them against xmin. We could
1147+
* filter against xmax, but it seems better not to do that much work
1148+
* while holding the ProcArrayLock.
1149+
*
1150+
* The other backend can add more subxids concurrently, but cannot
1151+
* remove any.Hence it's important to fetch nxids just once. Should
1152+
* be safe to use memcpy, though. (We needn't worry about missing any
1153+
* xids added concurrently, because they must postdate xmax.)
1154+
*
1155+
* Again, our own XIDs are not included in the snapshot.
1156+
*/
1157+
if (!suboverflowed&&proc!=MyProc)
1158+
{
1159+
if (proc->subxids.overflowed)
1160+
suboverflowed= true;
1161+
else
11591162
{
1160-
Assert(!snapshot->takenDuringRecovery);
1161-
memcpy(snapshot->subxip+subcount,
1162-
(void*)proc->subxids.xids,
1163-
nxids*sizeof(TransactionId));
1164-
subcount+=nxids;
1163+
intnxids=proc->subxids.nxids;
1164+
1165+
if (nxids>0)
1166+
{
1167+
memcpy(snapshot->subxip+subcount,
1168+
(void*)proc->subxids.xids,
1169+
nxids*sizeof(TransactionId));
1170+
subcount+=nxids;
1171+
}
11651172
}
11661173
}
11671174
}
11681175
}
1169-
1170-
/*
1171-
* If in recovery get any known assigned xids.
1172-
*/
1173-
if (snapshot->takenDuringRecovery)
1176+
else
11741177
{
1175-
Assert(count==0);
1176-
11771178
/*
11781179
* We store all xids directly into subxip[]. Here's why:
11791180
*

‎src/include/access/xlog.h‎

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -6,7 +6,7 @@
66
* Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
77
* Portions Copyright (c) 1994, Regents of the University of California
88
*
9-
* $PostgreSQL: pgsql/src/include/access/xlog.h,v 1.106 2010/04/12 09:52:29 heikki Exp $
9+
* $PostgreSQL: pgsql/src/include/access/xlog.h,v 1.107 2010/04/18 18:06:07 sriggs Exp $
1010
*/
1111
#ifndefXLOG_H
1212
#defineXLOG_H
@@ -278,6 +278,7 @@ extern void xlog_desc(StringInfo buf, uint8 xl_info, char *rec);
278278

279279
externvoidissue_xlog_fsync(intfd,uint32log,uint32seg);
280280

281+
externboolXLogConsistentState(void);
281282
externboolRecoveryInProgress(void);
282283
externboolXLogInsertAllowed(void);
283284
externTimestampTzGetLatestXLogTime(void);

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