Re: strange behavior of WAL files

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Atul Kumar <akumar14871(at)gmail(dot)com>
Cc: Jehan-Guillaume de Rorthais <jgdr(at)dalibo(dot)com>, pgsql-general <pgsql-general(at)lists(dot)postgresql(dot)org>
Subject: Re: strange behavior of WAL files
Date: 2021-06-04 14:11:20
Message-ID: 144409.1622815880@sss.pgh.pa.us
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Atul Kumar <akumar14871(at)gmail(dot)com> writes:
> once old WAL files of pg_xlog directory are archived in
> '/nfslogs/wal/' directory then these WAL files are getting generated
> with the same name in pg_xlog directory.

Are you sure you are describing the behavior accurately?

What I would expect to happen, once an old WAL file has been archived
and the server knows its contents are no longer needed, is for the
WAL file to be "recycled" by renaming it to have a name that's in-the-
future in the WAL name series, whereupon it will wait its turn to be
reused by future WAL writes. On most filesystems the rename as such
doesn't change the file's mod time, so you'll see files that seem
to be in-the-future according to their names, but have old timestamps.

(There's a limit on how many future WAL files we'll tee up this way,
so it's possible that an old one would just get deleted instead.
But the steady-state behavior is to just rotate them around.)

regards, tom lane

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