Horton

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

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Cc: Peter Smith <smithpb2250@gmail.com>, Ajin Cherian <itsajin@gmail.com>, Bertrand Drouvot <bertranddrouvot.pg@gmail.com>, shveta malik <shveta.malik@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, Nathan Bossart <nathandbossart@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2024-09-18T12:10:10Z
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 Mon, Sep 16, 2024 at 10:41 PM Bharath Rupireddy
<bharath.rupireddyforpostgres@gmail.com> wrote:
>
> Thanks for looking into this.
>
> On Mon, Sep 16, 2024 at 4:54 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> >
> > Why raise the ERROR just for timeout invalidation here and why not if
> > the slot is invalidated for other reasons? This raises the question of
> > what happens before this patch if the invalid slot is used from places
> > where we call ReplicationSlotAcquire(). I did a brief code analysis
> > and found that for StartLogicalReplication(), even if the error won't
> > occur in ReplicationSlotAcquire(), it would have been caught in
> > CreateDecodingContext(). I think that is where we should also add this
> > new error. Similarly, pg_logical_slot_get_changes_guts() and other
> > logical replication functions should be calling
> > CreateDecodingContext() which can raise the new ERROR. I am not sure
> > about how the invalid slots are handled during physical replication,
> > please check the behavior of that before this patch.
>
> When physical slots are invalidated due to wal_removed reason, the failure happens at a much later point for the streaming standbys while reading the requested WAL files like the following:
>
> 2024-09-16 16:29:52.416 UTC [876059] FATAL:  could not receive data from WAL stream: ERROR:  requested WAL segment 000000010000000000000005 has already been removed
> 2024-09-16 16:29:52.416 UTC [872418] LOG:  waiting for WAL to become available at 0/5002000
>
> At this point, despite the slot being invalidated, its wal_status can still come back to 'unreserved' even from 'lost', and the standby can catch up if removed WAL files are copied either by manually or by a tool/script to the primary's pg_wal directory. IOW, the physical slots invalidated due to wal_removed are *somehow* recoverable unlike the logical slots.
>
> IIUC, the invalidation of a slot implies that it is not guaranteed to hold any resources like WAL and XMINs. Does it also imply that the slot must be unusable?
>

If we can't hold the dead rows against xmin of the invalid slot, then
how can we make it usable even after copying the required WAL?

-- 
With Regards,
Amit Kapila.