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Commit285bd0a

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Remove unnecessary memcpy when reading WAL record fitting on page
When reading a WAL record, its contents are copied into an intermediatebuffer. However, doing so is not necessary if the record fits fullyinto the current page, saving one memcpy for each such record. Theallocation handling of the intermediate buffer is also now done onlywhen a record crosses a page boundary, shaving some extra cycles whenreading a WAL record.Author: Andrey LepikhovReviewed-by: Kyotaro Horiguchi, Heikki LinnakangasDiscussion:https://postgr.es/m/c2ea54dd-a1d3-80eb-ddbf-7e6f258e615e@postgrespro.ru
1 parent79376e0 commit285bd0a

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2 files changed

+13
-17
lines changed

2 files changed

+13
-17
lines changed

‎src/backend/access/transam/xlog.c

Lines changed: 0 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -4203,9 +4203,6 @@ CleanupBackupHistory(void)
42034203
* If no valid record is available, returns NULL, or fails if emode is PANIC.
42044204
* (emode must be either PANIC, LOG). In standby mode, retries until a valid
42054205
* record is available.
4206-
*
4207-
* The record is copied into readRecordBuf, so that on successful return,
4208-
* the returned record pointer always points there.
42094206
*/
42104207
staticXLogRecord*
42114208
ReadRecord(XLogReaderState*xlogreader,XLogRecPtrRecPtr,intemode,

‎src/backend/access/transam/xlogreader.c

Lines changed: 13 additions & 14 deletions
Original file line numberDiff line numberDiff line change
@@ -353,19 +353,6 @@ XLogReadRecord(XLogReaderState *state, XLogRecPtr RecPtr, char **errormsg)
353353
gotheader= false;
354354
}
355355

356-
/*
357-
* Enlarge readRecordBuf as needed.
358-
*/
359-
if (total_len>state->readRecordBufSize&&
360-
!allocate_recordbuf(state,total_len))
361-
{
362-
/* We treat this as a "bogus data" condition */
363-
report_invalid_record(state,"record length %u at %X/%X too long",
364-
total_len,
365-
(uint32) (RecPtr >>32), (uint32)RecPtr);
366-
gotoerr;
367-
}
368-
369356
len=XLOG_BLCKSZ-RecPtr %XLOG_BLCKSZ;
370357
if (total_len>len)
371358
{
@@ -375,6 +362,19 @@ XLogReadRecord(XLogReaderState *state, XLogRecPtr RecPtr, char **errormsg)
375362
char*buffer;
376363
uint32gotlen;
377364

365+
/*
366+
* Enlarge readRecordBuf as needed.
367+
*/
368+
if (total_len>state->readRecordBufSize&&
369+
!allocate_recordbuf(state,total_len))
370+
{
371+
/* We treat this as a "bogus data" condition */
372+
report_invalid_record(state,"record length %u at %X/%X too long",
373+
total_len,
374+
(uint32) (RecPtr >>32), (uint32)RecPtr);
375+
gotoerr;
376+
}
377+
378378
/* Copy the first fragment of the record from the first page. */
379379
memcpy(state->readRecordBuf,
380380
state->readBuf+RecPtr %XLOG_BLCKSZ,len);
@@ -479,7 +479,6 @@ XLogReadRecord(XLogReaderState *state, XLogRecPtr RecPtr, char **errormsg)
479479
state->EndRecPtr=RecPtr+MAXALIGN(total_len);
480480

481481
state->ReadRecPtr=RecPtr;
482-
memcpy(state->readRecordBuf,record,total_len);
483482
}
484483

485484
/*

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