Hi Mohan, On Tue, May 28, 2024 at 02:26:41PM -0400, Mohan NBSPS wrote: > Dear Community, > [...] > ``` > FATAL: could not receive data from WAL stream: ERROR: requested WAL > segment 000000010000004100000049 has already been removed > FATAL: the database system is starting up > ``` > > from my understanding, the WAL file is streamed over the network (secondary > pulls from primary) and creates a WAL file in the secondary. > then it replays the copied WAL file using a different process. > > in order for the local WAL file to go out of sync, > > 1. the primary removed the WAL file, the secondary was streaming > 2. the WAL file on the secondary got corrupted > 3 .... > > Questions > > - what do those error messages mean ? > - how can I prevent this from happening ? It means that, unless you have archived the required WAL segments somewhere and can recover them from there, your replica is now broken, and you will have to re-create it anew. You can prevent this by correctly configuring streaming replication either by using replication slots (not sure if that's already implemented in 9.5, actually - you should prioritize upgrading to a supported release while you are working this problem!), or by introducing a WAL archive[0] for replicas to retrieve WAL from that the primary has already evicted from its kept segments. Hth! [0]: https://www.postgresql.org/docs/9.5/runtime-config-wal.html#RUNTIME-CONFIG-WAL-ARCHIVING -- with best regards: - Johannes Truschnigg ( johannes@xxxxxxxxxxxxxxx ) www: https://johannes.truschnigg.info/
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