Re: Introduce XID age based replication slot invalidation

On Wed, Mar 25, 2026 at 12:17 PM Bharath Rupireddy <
bharath.rupireddyforpostgres@gmail.com> wrote:

> Hi,
>
> On Tue, Mar 24, 2026 at 11:50 PM Masahiko Sawada <sawada.mshk@gmail.com>
> wrote:
> >
> > > Please find the v3 patch for further review.
> >
> > Thank you for updating the patch. I think the patch is reasonably
> > simple and can avoid unnecessary overheads well due to XID-based
> > checks. Here are some comments:
>
> Thank you for reviewing the patch.
>
> > vacuum_get_cutoff() is also called by VACUUM FULL, CLUSTER, and
> > REPACK. I'm not sure that users would expect the slot invalidation
> > also in these commands. I think it's better to leave
> > vacuum_get_cutoff() a pure cutoff computation function and we can try
> > to invalidate slots in heap_vacuum_rel(). It requires additional
> > ReadNextTransactionId() but we can live with it, or we can make
> > vacuum_get_cutoffs() return the nextXID as well (stored in *cutoffs).
>
> +1. I chose to perform the slot invalidation in heap_vacuum_rel by
> getting the next txn ID and calling vacuum_get_cutoffs again when a
> slot gets invalidated. IMHO, this is simple than adding a flag and do
> the invalidation selectively in vacuum_get_cutoffs.
>
> >   if (TransactionIdPrecedes(oldestXmin, cutoffXID))
> > +   {
> > +       invalidated =
> InvalidateObsoleteReplicationSlots(RS_INVAL_XID_AGE,
> > +                                                        0,
> > +                                                        InvalidOid,
> > +
> InvalidTransactionId,
> > +                                                        nextXID);
> > +   }
> >
> > I think it's better to check the procArray->replication_slot_xmin and
> > procArray->replication_slot_catalog_xmin before iterating over each
> > slot. Otherwise, we would end up checking every slot even when a long
> > running transaction holds the oldestxmin back.
>
> +1. Changed.
>
> > +   if (!TransactionIdIsNormal(cutoffXID))
> > +       cutoffXID = FirstNormalTransactionId;
> >
> > These codes have the same comment but are doing a slightly different
> > thing. I guess the latter is missing '-'?
>
> Fixed the typo.
>
> I fixed a test error being reported in CI.
>
> Please find the attached v4 patch for further review.
>

 InvalidateObsoleteReplicationSlots(uint32 possible_causes,
    XLogSegNo oldestSegno, Oid dboid,
-   TransactionId snapshotConflictHorizon)
+   TransactionId snapshotConflictHorizon, TransactionId nextXID)

May be add TransactionId nextXID in a new line?

Thinking loud, vacuum doesn't  run on a hot_standby, that means this GUC is
not applicable for hot_standby. Is this intended? Why not call during
checkpoint/restorepoint itself like other slot invalidation checks?

Thanks,
Satya