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

On Wed, Sep 4, 2024 at 9:17 AM shveta malik <shveta(dot)malik(at)gmail(dot)com> wrote:
>
> On Tue, Sep 3, 2024 at 3:01 PM shveta malik <shveta(dot)malik(at)gmail(dot)com> wrote:
> >
> >
> > 1)
> > I see that ReplicationSlotAlter() will error out if the slot is
> > invalidated due to timeout. I have not tested it myself, but do you
> > know if slot-alter errors out for other invalidation causes as well?
> > Just wanted to confirm that the behaviour is consistent for all
> > invalidation causes.
>
> I was able to test this and as anticipated behavior is different. When
> slot is invalidated due to say 'wal_removed', I am still able to do
> 'alter' of that slot.
> Please see:
>
> Pub:
> slot_name | failover | synced | inactive_since |
> invalidation_reason
> -------------+----------+--------+----------------------------------+---------------------
> mysubnew1_1 | t | f | 2024-09-04 08:58:12.802278+05:30 |
> wal_removed
>
> Sub:
> newdb1=# alter subscription mysubnew1_1 disable;
> ALTER SUBSCRIPTION
>
> newdb1=# alter subscription mysubnew1_1 set (failover=false);
> ALTER SUBSCRIPTION
>
> Pub: (failover altered)
> slot_name | failover | synced | inactive_since |
> invalidation_reason
> -------------+----------+--------+----------------------------------+---------------------
> mysubnew1_1 | f | f | 2024-09-04 08:58:47.824471+05:30 |
> wal_removed
>
>
> while when invalidation_reason is 'inactive_timeout', it fails:
>
> Pub:
> slot_name | failover | synced | inactive_since |
> invalidation_reason
> -------------+----------+--------+----------------------------------+---------------------
> mysubnew1_1 | t | f | 2024-09-03 14:30:57.532206+05:30 |
> inactive_timeout
>
> Sub:
> newdb1=# alter subscription mysubnew1_1 disable;
> ALTER SUBSCRIPTION
>
> newdb1=# alter subscription mysubnew1_1 set (failover=false);
> ERROR: could not alter replication slot "mysubnew1_1": ERROR: can no
> longer get changes from replication slot "mysubnew1_1"
> DETAIL: The slot became invalid because it was inactive since
> 2024-09-04 08:54:20.308996+05:30, which is more than 0 seconds ago.
> HINT: You might need to increase "replication_slot_inactive_timeout.".
>
> I think the behavior should be same.
>

We should not allow the invalid replication slot to be altered
irrespective of the reason unless there is any benefit.

--
With Regards,
Amit Kapila.