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Tolerate timeline switches while "pg_basebackup -X fetch" is running.

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If you take a base backup from a standby server with "pg_basebackup -X
fetch", and the timeline switches while the backup is being taken, the
backup used to fail with an error "requested WAL segment %s has already
been removed". This is because the server-side code that sends over the
required WAL files would not construct the WAL filename with the correct
timeline after a switch.

Fix that by using readdir() to scan pg_xlog for all the WAL segments in the
range, regardless of timeline.

Also, include all timeline history files in the backup, if taken with
"-X fetch". That fixes another related bug: If a timeline switch happened
just before the backup was initiated in a standby, the WAL segment
containing the initial checkpoint record contains WAL from the older
timeline too. Recovery will not accept that without a timeline history file
that lists the older timeline.

Backpatch to 9.2. Versions prior to that were not affected as you could not
take a base backup from a standby before 9.2.
This commit is contained in:
Heikki Linnakangas
2013-01-03 19:51:00 +02:00
parent ee994272ca
commit b0daba57bb
4 changed files with 216 additions and 58 deletions
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23
src/backend/access/transam/xlog.c
View File

@ -2797,18 +2797,33 @@ PreallocXlogFiles(XLogRecPtr endptr)
}
/*
* Get the segno of the latest removed or recycled WAL segment.
* Returns 0/0 if no WAL segments have been removed since startup.
* Throws an error if the given log segment has already been removed or
* recycled. The caller should only pass a segment that it knows to have
* existed while the server has been running, as this function always
* succeeds if no WAL segments have been removed since startup.
* 'tli' is only used in the error message.
*/
void
XLogGetLastRemoved(XLogSegNo *segno)
CheckXLogRemoved(XLogSegNo segno, TimeLineID tli)
{
/* use volatile pointer to prevent code rearrangement */
volatile XLogCtlData *xlogctl = XLogCtl;
XLogSegNo lastRemovedSegNo;
SpinLockAcquire(&xlogctl->info_lck);
*segno = xlogctl->lastRemovedSegNo;
lastRemovedSegNo = xlogctl->lastRemovedSegNo;
SpinLockRelease(&xlogctl->info_lck);
if (segno <= lastRemovedSegNo)
{
char filename[MAXFNAMELEN];
XLogFileName(filename, tli, segno);
ereport(ERROR,
(errcode_for_file_access(),
errmsg("requested WAL segment %s has already been removed",
filename)));
}
}
/*