Re: Fetching timeline during recovery

> 23 июля 2019 г., в 21:05, Jehan-Guillaume de Rorthais <jgdr@dalibo.com> написал(а):
>
> Fetching the timeline from a standby could be useful in various situation.
> Either for backup tools [1] or failover tools during some kind of election
> process.
That backup tool is reading timeline from pg_control_checkpoint(). And formats WAL file name itself when necessary.

> Please, find in attachment a first trivial patch to support pg_walfile_name()
> and pg_walfile_name_offset() on a standby.

You just cannot format WAL file name for LSN when timeline changed. Because there are at least three WALs for that
point:previous, new and partial. However, reading TLI from checkpoint seems safe for backup purposes. 
The only reason for WAL-G to read that timeline is to mark backup invalid: if it's name is
base_00000001XXXXXXXXYY00000YYand timeline change happens, it should be named base_00000002XXXXXXXXYY00000YY
(consistencypoint is not on TLI 2), but WAL-G cannot rename backup during backup-push. 

Hope this information is useful. Thanks!

Best regards, Andrey Borodin.

[0] https://github.com/wal-g/wal-g/blob/master/internal/timeline.go#L39