On Mon, Dec 23, 2024 at 09:22:06AM +0530, mahendrakar s wrote: > Is there any psql utility function that returns the last removed wal > segment file? > I see there is a method: XLogGetLastRemovedSegno in xlog.c. > Would be happy to add a new psql function around it (similar to: > pg_walfile_name, pg_last_wal_replay_lsn, etc other utility functions > we have).
What's your use-case for it? I have to admit that finding out this information can be a bit annoying as it requires checking the state of archiving and the replication slots from which you would get a LSN (not a segment name). Of course, one can use pg_ls_waldir() these days and it would also work based on timeline number and even partial segments which are not removed by the checkpointer. That's more expensive than looking at a single counter in shmem. If you wrap a SQL function around that, the segment number would not be enough to guess which segment is removed: the timeline of the file removed should also be added. Hence XLogCtlData should be extended with a kind of lastRemovedSegTLI or equivalent to be able to rebuild the file name from the data in shared memory. Note that UpdateLastRemovedPtr() extracts the timeline number, does not store it. Also, note that UpdateLastRemovedPtr() has a small race condition when it comes to monitoring: it is called before the file is physically removed in RemoveOldXlogFiles(). It would not really matter much in practice, I guess.. -- Michael
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