On 7/23/19 2:59 PM, Andrey Borodin wrote: > >> 23 июля 2019 г., в 21:05, Jehan-Guillaume de Rorthais <j...@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.
We do the same [1]. >> 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_00000001XXXXXXXXYY00000YY and timeline change happens, it > should be named base_00000002XXXXXXXXYY00000YY (consistency point is not on > TLI 2), but WAL-G cannot rename backup during backup-push. Naming considerations aside, I don't think that a timeline switch during a standby backup is a good idea, mostly because it is (currently) not tested. We don't allow it in pgBackRest. [1] https://github.com/pgbackrest/pgbackrest/blob/release/2.15.1/lib/pgBackRest/Db.pm#L1008 -- -David da...@pgmasters.net
