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

On Tue, Feb 11, 2025 at 11:42 AM Zhijie Hou (Fujitsu)
<houzj(dot)fnst(at)fujitsu(dot)com> wrote:
>
> On Monday, February 10, 2025 8:03 PM Nisha Moond <nisha(dot)moond412(at)gmail(dot)com> wrote:
> >
> > On Sat, Feb 8, 2025 at 12:28 PM Zhijie Hou (Fujitsu) <houzj(dot)fnst(at)fujitsu(dot)com>
> > wrote:
> > >
> >
> > > 3.
> > >
> > > + if (cause & RS_INVAL_HORIZON)
> > > + {
> > > + if (!SlotIsLogical(s))
> > > + goto invalidation_marked;
> > >
> > > I am not sure if this logic is correct. Even if the slot would not be
> > > invalidated due to RS_INVAL_HORIZON, we should continue to check other
> > causes.
> > >
> >
> > Used goto here since we do not expect RS_INVAL_HORIZON to be combined
> > with any other "cause" and to keep the pgHead behavior.
> > However, with the bitflag approach, the code should be future-safe, so
> > replacing goto in v73 should handle this now.
>
> I think the following logic needs some adjustments.
>
> + if (invalidation_cause == RS_INVAL_NONE &&
> + (possible_causes & RS_INVAL_HORIZON))
> + {
> + if (SlotIsLogical(s) &&
> + /* invalid DB oid signals a shared relation */
> + (dboid == InvalidOid || dboid == s->data.database) &&
> + TransactionIdIsValid(initial_effective_xmin) &&
> + TransactionIdPrecedesOrEquals(initial_effective_xmin,
> + snapshotConflictHorizon))
> + invalidation_cause = RS_INVAL_HORIZON;
> + else if (TransactionIdIsValid(initial_catalog_effective_xmin) &&
> + TransactionIdPrecedesOrEquals(initial_catalog_effective_xmin,
> + snapshotConflictHorizon))
> + invalidation_cause = RS_INVAL_HORIZON;
> + }
>
> I think we assign RS_INVAL_HORIZON to invalidation_cause only when the slot is
> logical and the dboid is valid, but it is not guaranteed in the second if
> condition ("else if (TransactionIdIsValid(initial_catalog_effective_xmin)").
>
> Here is a top-up patch to fix this.

Thank you for reviewing and providing the fix! v75 addresses this bug
with a slightly different approach after introducing the new function
EvaluateSlotInvalidationCause().

--
Thanks,
Nisha