I have a test case with 3 PostgreSQL 9.5.5 servers, one master and two
hot standbys using standard streaming replication from the master.
wal_log_hints is not enabled, but all systems initialized to use
checksums.
The system is idle. I tear down the master, leaving the two standbys
orphaned at the same point in timeline 1.
I promote one of the standbys to master, switching it to timeline 2. I
shutdown the other standby, and attempt to run pg_rewind. It fails:
$ /usr/lib/postgresql/9.5/bin/pg_rewind
--target-pgdata=/var/lib/postgresql/9.5/main
--source-server='dbname=postgres host=10.0.4.212 port=5432
user=_juju_repl'
servers diverged at WAL position 0/5000AE0 on timeline 1
could not find previous WAL record at 0/5000AE0: invalid record length
at 0/5000AE0
Failure, exiting
This is what the pg_xlog on the new master looked like at that point:
postgres@juju-4ead0d-11:~/9.5/main/pg_xlog$ ls -al
total 81993
drwx------ 3 postgres postgres 9 Feb 15 08:55 .
drwx------ 19 postgres postgres 25 Feb 15 08:55 ..
-rw------- 1 postgres postgres 16777216 Feb 15 07:52 000000010000000000000002
-rw------- 1 postgres postgres 16777216 Feb 15 07:52 000000010000000000000003
-rw------- 1 postgres postgres 16777216 Feb 15 07:52 000000010000000000000004
-rw------- 1 postgres postgres 16777216 Feb 15 08:52
000000010000000000000005.partial
-rw------- 1 postgres postgres 41 Feb 15 08:55 00000002.history
-rw------- 1 postgres postgres 16777216 Feb 15 09:15 000000020000000000000005
drwx------ 2 postgres postgres 6 Feb 15 08:55 archive_status
Reconfiguring the standby to replicate from the new master and
restarting it works fine. The standby happily replicates and switches
to the new timeline. I can shut this standby down and run pg_rewind
again and it works fine.
--
Stuart Bishop <stuart@stuartbishop.net>
http://www.stuartbishop.net/
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