Horton

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

shveta malik <shveta.malik@gmail.com>

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From: shveta malik <shveta.malik@gmail.com>
To: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Bertrand Drouvot <bertranddrouvot.pg@gmail.com>, Nathan Bossart <nathandbossart@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, shveta malik <shveta.malik@gmail.com>
Date: 2024-03-26T04:00:32Z
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, Mar 25, 2024 at 12:43 PM shveta malik <shveta.malik@gmail.com> wrote:
>
> I have one concern, for synced slots on standby, how do we disallow
> invalidation due to inactive-timeout immediately after promotion?
>
> For synced slots, last_inactive_time and inactive_timeout are both
> set. Let's say I bring down primary for promotion of standby and then
> promote standby, there are chances that it may end up invalidating
> synced slots (considering standby is not brought down during promotion
> and thus inactive_timeout may already be past 'last_inactive_time').
>

On standby, if we decide to maintain valid last_inactive_time for
synced slots, then invalidation is correctly restricted in
InvalidateSlotForInactiveTimeout() for synced slots using the check:

        if (RecoveryInProgress() && slot->data.synced)
                return false;

But immediately after promotion, we can not rely on the above check
and thus possibility of synced slots invalidation is there. To
maintain consistent behavior regarding the setting of
last_inactive_time for synced slots, similar to user slots, one
potential solution to prevent this invalidation issue is to update the
last_inactive_time of all synced slots within the ShutDownSlotSync()
function during FinishWalRecovery(). This approach ensures that
promotion doesn't immediately invalidate slots, and henceforth, we
possess a correct last_inactive_time as a basis for invalidation going
forward. This will be equivalent to updating last_inactive_time during
restart (but without actual restart during promotion).
The plus point of maintaining last_inactive_time for synced slots
could be, this can provide data to the user on when last time the sync
was attempted on that particular slot by background slot sync worker
or SQl function. Thoughts?

thanks
Shveta