Re: Introduce XID age and inactive timeout based replication slot invalidation - Mailing list pgsql-hackers

On Thu, Sep 5, 2024 at 9:30 AM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Wed, Sep 4, 2024 at 9:17 AM shveta malik <shveta.malik@gmail.com> wrote:
> >
> > On Tue, Sep 3, 2024 at 3:01 PM shveta malik <shveta.malik@gmail.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.
>

Okay, then I think we need to change the existing behaviour of the
other invalidation causes which still allow alter-slot.

thanks
Shveta