Horton

Re: Introduce XID age and inactive timeout based replication slot invalidation

Nathan Bossart <nathandbossart@gmail.com>

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From: Nathan Bossart <nathandbossart@gmail.com>
To: Álvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Nisha Moond <nisha.moond412@gmail.com>, Peter Smith <smithpb2250@gmail.com>, vignesh C <vignesh21@gmail.com>, "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, Amit Kapila <amit.kapila16@gmail.com>, Shlok Kyal <shlok.kyal.oss@gmail.com>, "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, shveta malik <shveta.malik@gmail.com>, Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>, Ajin Cherian <itsajin@gmail.com>, Bertrand Drouvot <bertranddrouvot.pg@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2025-02-11T16:09:26Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Add a test for commit ac0e33136a using the injection point.

  2. Invalidate inactive replication slots.

  3. Fix incorrect slot type in BuildTupleHashTableExt

  4. Allow synced slots to have their inactive_since.

  5. Change last_inactive_time to inactive_since in pg_replication_slots.

  6. Track last_inactive_time in pg_replication_slots.

  7. Track invalidation_reason in pg_replication_slots.

  8. Add option force_initdb to PostgreSQL::Test::Cluster:init()

  9. Add a failover option to subscriptions.

  10. Allow setting failover property in the replication command.

  11. Allow to enable failover property for replication slots via SQL API.

  12. Track conflict_reason in pg_replication_slots.

  13. Log messages for replication slot acquisition and release.

  14. Remove vacuum_defer_cleanup_age

  15. Fix corruption due to vacuum_defer_cleanup_age underflowing 64bit xids

  16. meson: Add initial version of meson based build system

On Tue, Feb 11, 2025 at 03:22:49PM +0100, Álvaro Herrera wrote:
> I find this proposed patch a bit strange and I feel it needs more
> explanation.
> 
> When this thread started, Bharath justified his patches saying that a
> slot that's inactive for a very long time could be problematic because
> of XID wraparound.  Fine, that sounds a reasonable feature.  If you
> wanted to invalidate slots whose xmins were too old, I would support
> that.  He submitted that as his 0004 patch then.
> 
> However, he also chose to submit 0003 with invalidation based on a
> timeout.  This is far less convincing a feature to me.  The
> justification for the time out seems to be that ... it's difficult to
> have a one-size-fits-all value because size of disks vary. (???)
> Or something like that.  Really?  I mean -- yes, this will prevent
> problems in toy databases when run in developer's laptops.  It will not
> prevent any problems in production databases.  Do we really want a
> setting that is only useful for toy situations rather than production?
> 
> 
> Anyway, the thread is way too long, but after some initial pieces were
> committed, Nisha took over and submitting patches derived from Bharath's
> 0003, and at some point the initial 0004 was dropped.  But 0004 was the
> more useful one, I thought, so what's going on?
> 
> I'm baffled.

I agree, and I am also baffled because I think this discussion has happened
at least once already on this thread.  I still feel like the XID-based
parameter makes more sense.  For replication slots, two primary concerns
are 1) storage, for which we have max_slot_wal_keep_size and 2) XID
wraparound, for which we don't really have anything today.  A timeout might
be useful in some contexts, but if the goal is to prevent wraparound, why
not target that directly?

-- 
nathan