Horton

Re: BUG #17103: WAL segments are not removed after exceeding max_slot_wal_keep_size

Jeff Janes <jeff.janes@gmail.com>

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From: Jeff Janes <jeff.janes@gmail.com>
To: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Cc: Marcin Krupowicz <mk@071.ovh>, pgsql-bugs <pgsql-bugs@lists.postgresql.org>
Date: 2021-07-15T16:11:07Z
Lists: pgsql-bugs 
On Thu, Jul 15, 2021 at 1:22 AM Kyotaro Horiguchi <horikyota.ntt@gmail.com>
wrote:

> At Wed, 14 Jul 2021 19:10:26 -0400, Jeff Janes <jeff.janes@gmail.com>
> wrote in
> > On Tue, Jul 13, 2021 at 10:12 PM Kyotaro Horiguchi <
> horikyota.ntt@gmail.com>
> > wrote:
> > > Useless WAL files will be removd after a checkpoint runs.
> > >
> >
> > They should be, but they are not.  That is the bug.   They just hang
> > around, checkpoint after checkpoint.  Some of them do get cleaned up, to
> > make up for new ones created during that cycle.  It treats
> > max_slot_wal_keep the same way it treats wal_keep_size (but only if a
> > "lost" slot is hanging around).  If you drop the lost slot, only then
> does
> > it remove all the accumulated WAL at the next checkpoint.
>
> Thanks! I saw the issue here.  Some investigation showd me a doubious
> motion of XLogCtl->repliationSlotMinLSN.  Slot invalidation is
> forgetting to recalculate it and that misbehavior retreats the segment
> horizon.
>
> So the attached worked for me.  I'll repost the polished version
> including test.
>

Thank you.  That works for me.  But I did not test on Windows.

   * Some slots may have been gone,

"been invalidated" reads better than "been gone", and matches the wording
used elsewhere.

Cheers,

Jeff

Commits

  1. Close yet another race condition in replication slot test code

  2. Make new replication slot test code even less racy

  3. Make new replication slot test code less racy

  4. Advance old-segment horizon properly after slot invalidation