[GENERAL] Interesting streaming replication issue - Mailing list pgsql-general
Hi all,
I've got two servers (A,B) which are part of a streaming replication pair. A is the master, B is a hot standby. I'm sending archived WAL to a directory on A, B is reading it via SCP.
This all works fine normally. I'm on Redhat 7.3, running EDB 9.6.2 (I'm currently working to reproduce with standard 9.6)
We have recently seen a situation where B does not catch up when taken offline for maintenance.
When B is started we see the following in the logs:
2017-07-27 11:55:57 AEST [21432]: [979-1] user=,db=,client= (0:00000)LOG: restored log file "0000000C0000005A000000AA" from archive 2017-07-27 11:55:58 AEST [21432]: [980-1] user=,db=,client= (0:00000)LOG: restored log file "0000000C0000005A000000AB" from archive 2017-07-27 11:55:58 AEST [21432]: [981-1] user=,db=,client= (0:00000)LOG: restored log file "0000000C0000005A000000AC" from archive 2017-07-27 11:55:59 AEST [21432]: [982-1] user=,db=,client= (0:00000)LOG: restored log file "0000000C0000005A000000AD" from archive 2017-07-27 11:55:59 AEST [21432]: [983-1] user=,db=,client= (0:00000)LOG: restored log file "0000000C0000005A000000AE" from archive 2017-07-27 11:56:00 AEST [21432]: [984-1] user=,db=,client= (0:00000)LOG: restored log file "0000000C0000005A000000AF" from archive 2017-07-27 11:56:00 AEST [21432]: [985-1] user=,db=,client= (0:00000)LOG: restored log file "0000000C0000005A000000B0" from archive 2017-07-27 11:56:01 AEST [21432]: [986-1] user=,db=,client= (0:00000)LOG: restored log file "0000000C0000005A000000B1" from archive 2017-07-27 11:56:01 AEST [21432]: [987-1] user=,db=,client= (0:00000)LOG: restored log file "0000000C0000005A000000B2" from archive 2017-07-27 11:56:02 AEST [21432]: [988-1] user=,db=,client= (0:00000)LOG: restored log file "0000000C0000005A000000B3" from archive 2017-07-27 11:56:02 AEST [21432]: [989-1] user=,db=,client= (0:00000)LOG: restored log file "0000000C0000005A000000B4" from archive 2017-07-27 11:56:03 AEST [21432]: [990-1] user=,db=,client= (0:00000)LOG: restored log file "0000000C0000005A000000B5" from archive scp: /archive/xlog//0000000C0000005A000000B6: No such file or directory 2017-07-27 11:56:03 AEST [46191]: [1-1] user=,db=,client= (0:00000)LOG: started streaming WAL from primary at 5A/B5000000 on timeline 12 2017-07-27 11:56:03 AEST [46191]: [2-1] user=,db=,client= (0:XX000)FATAL: could not receive data from WAL stream: ERROR: requested WAL segment 0000000C0000005A000000B5 has already been removed scp: /archive/xlog//0000000D.history: No such file or directory scp: /archive/xlog//0000000C0000005A000000B6: No such file or directory 2017-07-27 11:56:04 AEST [46203]: [1-1] user=,db=,client= (0:00000)LOG: started streaming WAL from primary at 5A/B5000000 on timeline 12 2017-07-27 11:56:04 AEST [46203]: [2-1] user=,db=,client= (0:XX000)FATAL: could not receive data from WAL stream: ERROR: requested WAL segment 0000000C0000005A000000B5 has already been removed
This will loop indefinitely. At this stage the master reports no connected standbys in pg_stat_replication, and the standby has no running WAL receiver process.
This can be 'fixed' by running pg_switch_xlog() on the master, at which time a connection is seen from the standby and the logs show the following:
scp: /archive/xlog//0000000D.history: No such file or directory
2017-07-27 12:03:19 AEST [21432]: [1029-1] user=,db=,client= (0:00000)LOG: restored log file "0000000C0000005A000000B5" from archive
scp: /archive/xlog//0000000C0000005A000000B6: No such file or directory
2017-07-27 12:03:19 AEST [63141]: [1-1] user=,db=,client= (0:00000)LOG: started streaming WAL from primary at 5A/B5000000 on timeline 12
2017-07-27 12:03:19 AEST [63141]: [2-1] user=,db=,client= (0:XX000)FATAL: could not receive data from WAL stream: ERROR: requested WAL segment 0000000C0000005A000000B5 has already been removed
scp: /archive/xlog//0000000D.history: No such file or directory
2017-07-27 12:03:24 AEST [21432]: [1030-1] user=,db=,client= (0:00000)LOG: restored log file "0000000C0000005A000000B5" from archive
2017-07-27 12:03:24 AEST [21432]: [1031-1] user=,db=,client= (0:00000)LOG: restored log file "0000000C0000005A000000B6" from archive
scp: /archive/xlog//0000000C0000005A000000B7: No such file or directory
2017-07-27 12:03:25 AEST [21432]: [1032-1] user=,db=,client= (0:00000)LOG: unexpected pageaddr 56/E7000000 in log segment 0000000C0000005A000000B7, offset 0
2017-07-27 12:03:25 AEST [63196]: [1-1] user=,db=,client= (0:00000)LOG: started streaming WAL from primary
At this time replication is running as normal and all changes are streamed.
Am I missing something here, this seems very odd. One thing I have noticed is it only seems to be caused after a lot of WAL is produced and the pg_xlog directory is sitting at max_wal_size
James Sewell,
PostgreSQL Team Lead / Solutions Architect
Suite 112, Jones Bay Wharf, 26-32 Pirrama Road, Pyrmont NSW 2009
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