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

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.

Best Regards,
Hou zj