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Commit8c3cc86

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During WAL recovery, when reading a page that we intend to overwrite completely
from the WAL data, don't bother to physically read it; just have bufmgr.creturn a zeroed-out buffer instead. This speeds recovery significantly,and also avoids unnecessary failures when a page-to-be-overwritten has corruptpage headers on disk. This replaces a former kluge that accomplished thelatter by pretending zero_damaged_pages was always ON during WAL recovery;which was OK when the kluge was put in, but is unsafe when restoring a WALlog that was written with full_page_writes off.Heikki Linnakangas
1 parent8ec9438 commit8c3cc86

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3 files changed

+49
-13
lines changed

3 files changed

+49
-13
lines changed

‎src/backend/access/transam/xlogutils.c‎

Lines changed: 8 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -11,7 +11,7 @@
1111
* Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
1212
* Portions Copyright (c) 1994, Regents of the University of California
1313
*
14-
* $PostgreSQL: pgsql/src/backend/access/transam/xlogutils.c,v 1.49 2007/01/05 22:19:24 momjian Exp $
14+
* $PostgreSQL: pgsql/src/backend/access/transam/xlogutils.c,v 1.50 2007/05/02 23:18:03 tgl Exp $
1515
*
1616
*-------------------------------------------------------------------------
1717
*/
@@ -206,7 +206,9 @@ XLogCheckInvalidPages(void)
206206
* If "init" is true then the caller intends to rewrite the page fully
207207
* using the info in the XLOG record. In this case we will extend the
208208
* relation if needed to make the page exist, and we will not complain about
209-
* the page being "new" (all zeroes).
209+
* the page being "new" (all zeroes); in fact, we usually will supply a
210+
* zeroed buffer without reading the page at all, so as to avoid unnecessary
211+
* failure if the page is present on disk but has corrupt headers.
210212
*
211213
* If "init" is false then the caller needs the page to be valid already.
212214
* If the page doesn't exist or contains zeroes, we return InvalidBuffer.
@@ -226,7 +228,10 @@ XLogReadBuffer(Relation reln, BlockNumber blkno, bool init)
226228
if (blkno<lastblock)
227229
{
228230
/* page exists in file */
229-
buffer=ReadBuffer(reln,blkno);
231+
if (init)
232+
buffer=ReadOrZeroBuffer(reln,blkno);
233+
else
234+
buffer=ReadBuffer(reln,blkno);
230235
}
231236
else
232237
{

‎src/backend/storage/buffer/bufmgr.c‎

Lines changed: 39 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/backend/storage/buffer/bufmgr.c,v 1.216 2007/03/3018:34:55 mha Exp $
11+
* $PostgreSQL: pgsql/src/backend/storage/buffer/bufmgr.c,v 1.217 2007/05/02 23:18:03 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -17,6 +17,12 @@
1717
*and pin it so that no one can destroy it while this process
1818
*is using it.
1919
*
20+
* ReadOrZeroBuffer() -- like ReadBuffer, but if the page is not already in
21+
*cache we don't read it, but just return a zeroed-out buffer. Useful
22+
*when the caller intends to fill the page from scratch, since this
23+
*saves I/O and avoids unnecessary failure if the page-on-disk has
24+
*corrupt page headers.
25+
*
2026
* ReleaseBuffer() -- unpin a buffer
2127
*
2228
* MarkBufferDirty() -- mark a pinned buffer's contents as "dirty".
@@ -87,6 +93,8 @@ static volatile BufferDesc *PinCountWaitBuf = NULL;
8793
externPgStat_MsgBgWriterBgWriterStats;
8894

8995

96+
staticBufferReadBuffer_common(Relationreln,BlockNumberblockNum,
97+
boolzeroPage);
9098
staticboolPinBuffer(volatileBufferDesc*buf);
9199
staticvoidPinBuffer_Locked(volatileBufferDesc*buf);
92100
staticvoidUnpinBuffer(volatileBufferDesc*buf,
@@ -120,6 +128,27 @@ static void AtProcExit_Buffers(int code, Datum arg);
120128
*/
121129
Buffer
122130
ReadBuffer(Relationreln,BlockNumberblockNum)
131+
{
132+
returnReadBuffer_common(reln,blockNum, false);
133+
}
134+
135+
/*
136+
* ReadOrZeroBuffer -- like ReadBuffer, but if the page isn't in buffer
137+
*cache already, it's filled with zeros instead of reading it from
138+
*disk. The caller is expected to overwrite the whole buffer,
139+
*so that the current page contents are not interesting.
140+
*/
141+
Buffer
142+
ReadOrZeroBuffer(Relationreln,BlockNumberblockNum)
143+
{
144+
returnReadBuffer_common(reln,blockNum, true);
145+
}
146+
147+
/*
148+
* ReadBuffer_common -- common logic for ReadBuffer and ReadOrZeroBuffer
149+
*/
150+
staticBuffer
151+
ReadBuffer_common(Relationreln,BlockNumberblockNum,boolzeroPage)
123152
{
124153
volatileBufferDesc*bufHdr;
125154
BlockbufBlock;
@@ -253,17 +282,18 @@ ReadBuffer(Relation reln, BlockNumber blockNum)
253282
}
254283
else
255284
{
256-
smgrread(reln->rd_smgr,blockNum, (char*)bufBlock);
285+
/*
286+
* Read in the page, unless the caller intends to overwrite it
287+
* and just wants us to allocate a buffer.
288+
*/
289+
if (zeroPage)
290+
MemSet((char*)bufBlock,0,BLCKSZ);
291+
else
292+
smgrread(reln->rd_smgr,blockNum, (char*)bufBlock);
257293
/* check for garbage data */
258294
if (!PageHeaderIsValid((PageHeader)bufBlock))
259295
{
260-
/*
261-
* During WAL recovery, the first access to any data page should
262-
* overwrite the whole page from the WAL; so a clobbered page
263-
* header is not reason to fail. Hence, when InRecovery we may
264-
* always act as though zero_damaged_pages is ON.
265-
*/
266-
if (zero_damaged_pages||InRecovery)
296+
if (zero_damaged_pages)
267297
{
268298
ereport(WARNING,
269299
(errcode(ERRCODE_DATA_CORRUPTED),

‎src/include/storage/bufmgr.h‎

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
77
* Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
88
* Portions Copyright (c) 1994, Regents of the University of California
99
*
10-
* $PostgreSQL: pgsql/src/include/storage/bufmgr.h,v 1.102 2007/01/05 22:19:57 momjian Exp $
10+
* $PostgreSQL: pgsql/src/include/storage/bufmgr.h,v 1.103 2007/05/02 23:18:03 tgl Exp $
1111
*
1212
*-------------------------------------------------------------------------
1313
*/
@@ -111,6 +111,7 @@ extern DLLIMPORT int32 *LocalRefCount;
111111
* prototypes for functions in bufmgr.c
112112
*/
113113
externBufferReadBuffer(Relationreln,BlockNumberblockNum);
114+
externBufferReadOrZeroBuffer(Relationreln,BlockNumberblockNum);
114115
externvoidReleaseBuffer(Bufferbuffer);
115116
externvoidUnlockReleaseBuffer(Bufferbuffer);
116117
externvoidMarkBufferDirty(Bufferbuffer);

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