Re: Pg_rewind cannot load history wal

Whenever you do switch-over, postgres-wal creates a new timeline, which simplifies managing PITR process.

During switch-over(promoting B as master) you had some delta records written to A, that’s where it causes this timeline issue.

Now since A had some delta records, it can’t replicate from B and hence you are getting that issue.

Now once your master A can’t become slave of B.
— A

> On 02-Aug-2018, at 2:39 AM, Richard Schmidt <Richard(dot)Schmidt(at)metservice(dot)com> wrote:
>
> We have been struggling to get pr_rewind to work. In desperation we have been trying to make the use case as simple as possibleJ
>
> We have two databases servers running Postgres 10 on two different machine in the normal Primary/Standby configuration.
> Both machines write their WAL archive logs to the same shared drive (called /ice_dev/wal_archive).
> The configuration has the following terms
> archive_mode = always
> archive_command = 'test ! -f /ice-dev/wal_archive/%f && cp %p /ice-dev/wal_archive/%f'
> full_page_writes = on
> wal_log_hints = on
> Checksums are enabled
>
> Our procedure that runs on machine A and B is as follows:
>
> Build new databases on A and B, and configure A as Primary and B as Standby databases.
> Make some changes to the A (the primary) and check that they are replicated to the B (the standby)
> Promote B to be the new primary
> Switch of the A (the original primary)
> Add the replication slot to B (the new primary) for A (soon to be standby)
> Add a recovery.conf to A (soon to be standby). File contains recovery_target_timeline = 'latest' and restore_command = 'cp /ice-dev/wal_archive/%f "%p"
> Run pg_rewind on A – this appears to work as it returns the message ‘source and target cluster are on the same timeline no rewind required’;
> Start up server A (now a slave)
>
> At this point A is in a read only mode but not replicating. Its logs contain the following repeating message
>
> 2018-08-01 20:30:58 UTC [7257]: [1] user=,db=,app=,client= FATAL: could not start WAL streaming: ERROR: requested starting point 0/6000000 on timeline 1 is not in this server's history
> DETAIL: This server's history forked from timeline 1 at 0/57639D0.
> cp: cannot stat ‘/ice-dev/wal_archive/00000002.history’: No such file or directory
> cp: cannot stat ‘/ice-dev/wal_archive/00000003.history’: No such file or directory
> cp: cannot stat ‘/ice-dev/wal_archive/00000002.history’: No such file or directory
> 2018-08-01 20:30:58 UTC [6840]: [48] user=,db=,app=,client= LOG: new timeline 2 forked off current database system timeline 1 before current recovery point 0/6000098
> cp: cannot stat ‘/ice-dev/wal_archive/000000010000000000000006’: No such file or directory
>
> We can see the 00000002.history file in B’s wal directory…..but it never appears in the wal_archive directory – not even if we issue a checkout or even restart the server.
> 00000003.history does not appear to exist on either of the machines.
>
> Any ideas what we are doing wrong?
> Thanks. Richard
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