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Commite50cda7

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Use pg_rewind when target timeline was switched
Allow pg_rewind to work when target timeline was switched. Nowuser can return promoted standby to old master.Target timeline history becomes a global variable. Indexin target timeline history is used in function interfaces instead ofspecifying TLI directly. Thus, SimpleXLogPageRead() can easily startreading XLOGs from next timeline when current timeline ends.Author: Alexander KorotkovReview: Michael Paquier
1 parent0e0776b commite50cda7

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5 files changed

+181
-77
lines changed

5 files changed

+181
-77
lines changed

‎doc/src/sgml/ref/pg_rewind.sgml

Lines changed: 11 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -61,13 +61,17 @@ PostgreSQL documentation
6161
<application>pg_rewind</> examines the timeline histories of the source
6262
and target clusters to determine the point where they diverged, and
6363
expects to find WAL in the target cluster's <filename>pg_xlog</> directory
64-
reaching all the way back to the point of divergence. In the typical
65-
failover scenario where the target cluster was shut down soon after the
66-
divergence, that is not a problem, but if the target cluster had run for a
67-
long time after the divergence, the old WAL files might not be present
68-
anymore. In that case, they can be manually copied from the WAL archive to
69-
the <filename>pg_xlog</> directory. Fetching missing files from a WAL
70-
archive automatically is currently not supported.
64+
reaching all the way back to the point of divergence. The point of divergence
65+
could be found either on target timeline, source timeline or their common
66+
ancestor. In the typical failover scenario where the target cluster was
67+
shut down soon after the divergence, that is not a problem, but if the
68+
target cluster had run for a long time after the divergence, the old WAL
69+
files might not be present anymore. In that case, they can be manually
70+
copied from the WAL archive to the <filename>pg_xlog</> directory. Fetching
71+
missing files from a WAL archive automatically is currently not supported.
72+
Besides, <application>pg_rewind</> use cases are not limited by failover.
73+
For instance, standby server could be promoted, run some writes and
74+
then be returned back as stanby.
7175
</para>
7276

7377
<para>

‎src/bin/pg_rewind/Makefile

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
#
99
#-------------------------------------------------------------------------
1010

11-
PGFILEDESC = "pg_rewind -repurpose an old master server as standby"
11+
PGFILEDESC = "pg_rewind -synchronize a data directory with another one forked from"
1212
PGAPPICON = win32
1313

1414
subdir = src/bin/pg_rewind

‎src/bin/pg_rewind/parsexlog.c

Lines changed: 27 additions & 12 deletions
Original file line numberDiff line numberDiff line change
@@ -45,7 +45,7 @@ static char xlogfpath[MAXPGPATH];
4545
typedefstructXLogPageReadPrivate
4646
{
4747
constchar*datadir;
48-
TimeLineIDtli;
48+
inttliIndex;
4949
}XLogPageReadPrivate;
5050

5151
staticintSimpleXLogPageRead(XLogReaderState*xlogreader,
@@ -55,11 +55,11 @@ static int SimpleXLogPageRead(XLogReaderState *xlogreader,
5555

5656
/*
5757
* Read WAL from the datadir/pg_xlog, starting from 'startpoint' on timeline
58-
*'tli', until 'endpoint'. Make note of the data blocks touched by the WAL
59-
* records, and return them in a page map.
58+
*index 'tliIndex' in target timeline history, until 'endpoint'. Make note of
59+
*the data blocks touched by the WALrecords, and return them in a page map.
6060
*/
6161
void
62-
extractPageMap(constchar*datadir,XLogRecPtrstartpoint,TimeLineIDtli,
62+
extractPageMap(constchar*datadir,XLogRecPtrstartpoint,inttliIndex,
6363
XLogRecPtrendpoint)
6464
{
6565
XLogRecord*record;
@@ -68,7 +68,7 @@ extractPageMap(const char *datadir, XLogRecPtr startpoint, TimeLineID tli,
6868
XLogPageReadPrivateprivate;
6969

7070
private.datadir=datadir;
71-
private.tli=tli;
71+
private.tliIndex=tliIndex;
7272
xlogreader=XLogReaderAllocate(&SimpleXLogPageRead,&private);
7373
if (xlogreader==NULL)
7474
pg_fatal("out of memory\n");
@@ -112,7 +112,7 @@ extractPageMap(const char *datadir, XLogRecPtr startpoint, TimeLineID tli,
112112
* doing anything with the record itself.
113113
*/
114114
XLogRecPtr
115-
readOneRecord(constchar*datadir,XLogRecPtrptr,TimeLineIDtli)
115+
readOneRecord(constchar*datadir,XLogRecPtrptr,inttliIndex)
116116
{
117117
XLogRecord*record;
118118
XLogReaderState*xlogreader;
@@ -121,7 +121,7 @@ readOneRecord(const char *datadir, XLogRecPtr ptr, TimeLineID tli)
121121
XLogRecPtrendptr;
122122

123123
private.datadir=datadir;
124-
private.tli=tli;
124+
private.tliIndex=tliIndex;
125125
xlogreader=XLogReaderAllocate(&SimpleXLogPageRead,&private);
126126
if (xlogreader==NULL)
127127
pg_fatal("out of memory\n");
@@ -152,7 +152,7 @@ readOneRecord(const char *datadir, XLogRecPtr ptr, TimeLineID tli)
152152
* Find the previous checkpoint preceding given WAL position.
153153
*/
154154
void
155-
findLastCheckpoint(constchar*datadir,XLogRecPtrforkptr,TimeLineIDtli,
155+
findLastCheckpoint(constchar*datadir,XLogRecPtrforkptr,inttliIndex,
156156
XLogRecPtr*lastchkptrec,TimeLineID*lastchkpttli,
157157
XLogRecPtr*lastchkptredo)
158158
{
@@ -173,7 +173,7 @@ findLastCheckpoint(const char *datadir, XLogRecPtr forkptr, TimeLineID tli,
173173
forkptr+= (forkptr %XLogSegSize==0) ?SizeOfXLogLongPHD :SizeOfXLogShortPHD;
174174

175175
private.datadir=datadir;
176-
private.tli=tli;
176+
private.tliIndex=tliIndex;
177177
xlogreader=XLogReaderAllocate(&SimpleXLogPageRead,&private);
178178
if (xlogreader==NULL)
179179
pg_fatal("out of memory\n");
@@ -236,9 +236,11 @@ SimpleXLogPageRead(XLogReaderState *xlogreader, XLogRecPtr targetPagePtr,
236236
{
237237
XLogPageReadPrivate*private= (XLogPageReadPrivate*)xlogreader->private_data;
238238
uint32targetPageOff;
239-
XLogSegNotargetSegNoPG_USED_FOR_ASSERTS_ONLY;
239+
XLogRecPtrtargetSegEnd;
240+
XLogSegNotargetSegNo;
240241

241242
XLByteToSeg(targetPagePtr,targetSegNo);
243+
XLogSegNoOffsetToRecPtr(targetSegNo+1,0,targetSegEnd);
242244
targetPageOff=targetPagePtr %XLogSegSize;
243245

244246
/*
@@ -257,7 +259,20 @@ SimpleXLogPageRead(XLogReaderState *xlogreader, XLogRecPtr targetPagePtr,
257259
{
258260
charxlogfname[MAXFNAMELEN];
259261

260-
XLogFileName(xlogfname,private->tli,xlogreadsegno);
262+
/*
263+
* Since incomplete segments are copied into next timelines, switch to
264+
* the timeline holding the required segment. Assuming this scan can be
265+
* done both forward and backward, consider also switching timeline
266+
* accordingly.
267+
*/
268+
while (private->tliIndex<targetNentries-1&&
269+
targetHistory[private->tliIndex].end<targetSegEnd)
270+
private->tliIndex++;
271+
while (private->tliIndex>0&&
272+
targetHistory[private->tliIndex].begin >=targetSegEnd)
273+
private->tliIndex--;
274+
275+
XLogFileName(xlogfname,targetHistory[private->tliIndex].tli,xlogreadsegno);
261276

262277
snprintf(xlogfpath,MAXPGPATH,"%s/"XLOGDIR"/%s",private->datadir,xlogfname);
263278

@@ -293,7 +308,7 @@ SimpleXLogPageRead(XLogReaderState *xlogreader, XLogRecPtr targetPagePtr,
293308

294309
Assert(targetSegNo==xlogreadsegno);
295310

296-
*pageTLI=private->tli;
311+
*pageTLI=targetHistory[private->tliIndex].tli;
297312
returnXLOG_BLCKSZ;
298313
}
299314

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