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Commit5ae1572

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Fix O(N^2) stat() calls when recycling WAL segments
The counter tracking the last segment number recycled was gettinginitialized when recycling one single segment, while it should be usedacross a full cycle of segments recycled to prevent useless checksrelated to entries already recycled.This performance issue has been introduced byb2a5545, and it was firstimplemented in61b8614.No backpatch is done per the lack of field complaints.Reported-by: Andres Freund, Thomas MunroAuthor: Michael PaquierReviewed-By: Andres FreundDiscussion:https://postgr.es/m/20170621211016.eln6cxxp3jrv7m4m@alap3.anarazel.deDiscussion:https://postgr.es/m/CA+hUKG+DRiF9z1_MU4fWq+RfJMxP7zjoptfcmuCFPeO4JM2iVg@mail.gmail.com
1 parent5e5f4fc commit5ae1572

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1 file changed

+31
-30
lines changed
  • src/backend/access/transam

1 file changed

+31
-30
lines changed

‎src/backend/access/transam/xlog.c‎

Lines changed: 31 additions & 30 deletions
Original file line numberDiff line numberDiff line change
@@ -930,7 +930,8 @@ static void XLogFileClose(void);
930930
staticvoidPreallocXlogFiles(XLogRecPtrendptr);
931931
staticvoidRemoveTempXlogFiles(void);
932932
staticvoidRemoveOldXlogFiles(XLogSegNosegno,XLogRecPtrlastredoptr,XLogRecPtrendptr);
933-
staticvoidRemoveXlogFile(constchar*segname,XLogRecPtrlastredoptr,XLogRecPtrendptr);
933+
staticvoidRemoveXlogFile(constchar*segname,XLogSegNorecycleSegNo,
934+
XLogSegNo*endlogSegNo);
934935
staticvoidUpdateLastRemovedPtr(char*filename);
935936
staticvoidValidateXLOGDirectoryStructure(void);
936937
staticvoidCleanupBackupHistory(void);
@@ -4055,6 +4056,12 @@ RemoveOldXlogFiles(XLogSegNo segno, XLogRecPtr lastredoptr, XLogRecPtr endptr)
40554056
DIR*xldir;
40564057
structdirent*xlde;
40574058
charlastoff[MAXFNAMELEN];
4059+
XLogSegNoendlogSegNo;
4060+
XLogSegNorecycleSegNo;
4061+
4062+
/* Initialize info about where to try to recycle to */
4063+
XLByteToSeg(endptr,endlogSegNo,wal_segment_size);
4064+
recycleSegNo=XLOGfileslop(lastredoptr);
40584065

40594066
/*
40604067
* Construct a filename of the last segment to be kept. The timeline ID
@@ -4093,7 +4100,7 @@ RemoveOldXlogFiles(XLogSegNo segno, XLogRecPtr lastredoptr, XLogRecPtr endptr)
40934100
/* Update the last removed location in shared memory first */
40944101
UpdateLastRemovedPtr(xlde->d_name);
40954102

4096-
RemoveXlogFile(xlde->d_name,lastredoptr,endptr);
4103+
RemoveXlogFile(xlde->d_name,recycleSegNo,&endlogSegNo);
40974104
}
40984105
}
40994106
}
@@ -4123,13 +4130,21 @@ RemoveNonParentXlogFiles(XLogRecPtr switchpoint, TimeLineID newTLI)
41234130
structdirent*xlde;
41244131
charswitchseg[MAXFNAMELEN];
41254132
XLogSegNoendLogSegNo;
4133+
XLogSegNoswitchLogSegNo;
4134+
XLogSegNorecycleSegNo;
41264135

4127-
XLByteToPrevSeg(switchpoint,endLogSegNo,wal_segment_size);
4136+
/*
4137+
* Initialize info about where to begin the work. This will recycle,
4138+
* somewhat arbitrarily, 10 future segments.
4139+
*/
4140+
XLByteToPrevSeg(switchpoint,switchLogSegNo,wal_segment_size);
4141+
XLByteToSeg(switchpoint,endLogSegNo,wal_segment_size);
4142+
recycleSegNo=endLogSegNo+10;
41284143

41294144
/*
41304145
* Construct a filename of the last segment to be kept.
41314146
*/
4132-
XLogFileName(switchseg,newTLI,endLogSegNo,wal_segment_size);
4147+
XLogFileName(switchseg,newTLI,switchLogSegNo,wal_segment_size);
41334148

41344149
elog(DEBUG2,"attempting to remove WAL segments newer than log file %s",
41354150
switchseg);
@@ -4157,7 +4172,7 @@ RemoveNonParentXlogFiles(XLogRecPtr switchpoint, TimeLineID newTLI)
41574172
* - but seems safer to let them be archived and removed later.
41584173
*/
41594174
if (!XLogArchiveIsReady(xlde->d_name))
4160-
RemoveXlogFile(xlde->d_name,InvalidXLogRecPtr,switchpoint);
4175+
RemoveXlogFile(xlde->d_name,recycleSegNo,&endLogSegNo);
41614176
}
41624177
}
41634178

@@ -4167,36 +4182,22 @@ RemoveNonParentXlogFiles(XLogRecPtr switchpoint, TimeLineID newTLI)
41674182
/*
41684183
* Recycle or remove a log file that's no longer needed.
41694184
*
4170-
* endptr is current (or recent) end of xlog, and lastredoptr is the
4171-
* redo pointer of the last checkpoint. These are used to determine
4172-
* whether we want to recycle rather than delete no-longer-wanted log files.
4173-
* If lastredoptr is not known, pass invalid, and the function will recycle,
4174-
* somewhat arbitrarily, 10 future segments.
4185+
* segname is the name of the segment to recycle or remove. recycleSegNo
4186+
* is the segment number to recycle up to. endlogSegNo is the segment
4187+
* number of the current (or recent) end of WAL.
4188+
*
4189+
* endlogSegNo gets incremented if the segment is recycled so as it is not
4190+
* checked again with future callers of this function.
41754191
*/
41764192
staticvoid
4177-
RemoveXlogFile(constchar*segname,XLogRecPtrlastredoptr,XLogRecPtrendptr)
4193+
RemoveXlogFile(constchar*segname,XLogSegNorecycleSegNo,
4194+
XLogSegNo*endlogSegNo)
41784195
{
41794196
charpath[MAXPGPATH];
41804197
#ifdefWIN32
41814198
charnewpath[MAXPGPATH];
41824199
#endif
41834200
structstatstatbuf;
4184-
XLogSegNoendlogSegNo;
4185-
XLogSegNorecycleSegNo;
4186-
4187-
if (wal_recycle)
4188-
{
4189-
/*
4190-
* Initialize info about where to try to recycle to.
4191-
*/
4192-
XLByteToSeg(endptr,endlogSegNo,wal_segment_size);
4193-
if (lastredoptr==InvalidXLogRecPtr)
4194-
recycleSegNo=endlogSegNo+10;
4195-
else
4196-
recycleSegNo=XLOGfileslop(lastredoptr);
4197-
}
4198-
else
4199-
recycleSegNo=0;/* keep compiler quiet */
42004201

42014202
snprintf(path,MAXPGPATH,XLOGDIR"/%s",segname);
42024203

@@ -4206,17 +4207,17 @@ RemoveXlogFile(const char *segname, XLogRecPtr lastredoptr, XLogRecPtr endptr)
42064207
* symbolic links pointing to a separate archive directory.
42074208
*/
42084209
if (wal_recycle&&
4209-
endlogSegNo <=recycleSegNo&&
4210+
*endlogSegNo <=recycleSegNo&&
42104211
lstat(path,&statbuf)==0&&S_ISREG(statbuf.st_mode)&&
4211-
InstallXLogFileSegment(&endlogSegNo,path,
4212+
InstallXLogFileSegment(endlogSegNo,path,
42124213
true,recycleSegNo, true))
42134214
{
42144215
ereport(DEBUG2,
42154216
(errmsg("recycled write-ahead log file \"%s\"",
42164217
segname)));
42174218
CheckpointStats.ckpt_segs_recycled++;
42184219
/* Needn't recheck that slot on future iterations */
4219-
endlogSegNo++;
4220+
(*endlogSegNo)++;
42204221
}
42214222
else
42224223
{

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