Horton

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

Bertrand Drouvot <bertranddrouvot.pg@gmail.com>

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From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
To: shveta malik <shveta.malik@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>, Nathan Bossart <nathandbossart@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2024-03-26T10:20:50Z
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

Hi,

On Tue, Mar 26, 2024 at 03:17:36PM +0530, shveta malik wrote:
> On Tue, Mar 26, 2024 at 1:54 PM Bertrand Drouvot
> <bertranddrouvot.pg@gmail.com> wrote:
> >
> > Hi,
> >
> > On Tue, Mar 26, 2024 at 01:37:21PM +0530, Amit Kapila wrote:
> > > On Tue, Mar 26, 2024 at 1:15 PM Bertrand Drouvot
> > > <bertranddrouvot.pg@gmail.com> wrote:
> > > >
> > > > 2 ===
> > > >
> > > > It looks like inactive_since is set to the current timestamp on the standby
> > > > each time the sync worker does a cycle:
> > > >
> > > > primary:
> > > >
> > > > postgres=# select slot_name,inactive_since from pg_replication_slots where failover = 't';
> > > >   slot_name  |        inactive_since
> > > > -------------+-------------------------------
> > > >  lsub27_slot | 2024-03-26 07:39:19.745517+00
> > > >  lsub28_slot | 2024-03-26 07:40:24.953826+00
> > > >
> > > > standby:
> > > >
> > > > postgres=# select slot_name,inactive_since from pg_replication_slots where failover = 't';
> > > >   slot_name  |        inactive_since
> > > > -------------+-------------------------------
> > > >  lsub27_slot | 2024-03-26 07:43:56.387324+00
> > > >  lsub28_slot | 2024-03-26 07:43:56.387338+00
> > > >
> > > > I don't think that should be the case.
> > > >
> > >
> > > But why? This is exactly what we discussed in another thread where we
> > > agreed to update inactive_since even for sync slots.
> >
> > Hum, I thought we agreed to "sync" it and to "update it to current time"
> > only at promotion time.
> 
> I think there may have been some misunderstanding here.

Indeed ;-)

> But now if I
> rethink this, I am fine with 'inactive_since' getting synced from
> primary to standby. But if we do that, we need to add docs stating
> "inactive_since" represents primary's inactivity and not standby's
> slots inactivity for synced slots.

Yeah sure.

> The reason for this clarification
> is that the synced slot might be generated much later, yet
> 'inactive_since' is synced from the primary, potentially indicating a
> time considerably earlier than when the synced slot was actually
> created.

Right.

> Another approach could be that "inactive_since" for synced slot
> actually gives its own inactivity data rather than giving primary's
> slot data. We update inactive_since on standby only at 3 occasions:
> 1) at the time of creation of the synced slot.
> 2) during standby restart.
> 3) during promotion of standby.
> 
> I have attached a sample patch for this idea as.txt file.

Thanks!

> I am fine with any of these approaches.  One gives data synced from
> primary for synced slots, while another gives actual inactivity data
> of synced slots.

What about another approach?: inactive_since gives data synced from primary for
synced slots and another dedicated field (could be added later...) could
represent what you suggest as the other option.

Another cons of updating inactive_since at the current time during each slot
sync cycle is that calling GetCurrentTimestamp() very frequently
(during each sync cycle of very active slots) could be too costly.

Regards,

-- 
Bertrand Drouvot
PostgreSQL Contributors Team
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