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

On Mon, Mar 11, 2024 at 11:26 AM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> > Hm. I get the concern. Are you okay with having inavlidation_reason
> > separately for both logical and physical slots? In such a case,
> > logical slots that got invalidated on the standby will have duplicate
> > info in conflict_reason and invalidation_reason, is this fine?
> >
>
> If we have duplicate information in two columns that could be
> confusing for users. BTW, isn't the recovery conflict occur only
> because of rows_removed and wal_level_insufficient reasons? The
> wal_removed or the new reasons you are proposing can't happen because
> of recovery conflict. Am, I missing something here?

My understanding aligns with yours that the rows_removed and
wal_level_insufficient invalidations can occur only upon recovery
conflict.

FWIW, a test named 'synchronized slot has been invalidated' in
040_standby_failover_slots_sync.pl inappropriately uses
conflict_reason = 'wal_removed' logical slot on standby. As per the
above understanding, it's inappropriate to use conflict_reason here
because wal_removed invalidation doesn't conflict with recovery.

> > Another idea is to make 'conflict_reason text' as a 'conflicting
> > boolean' again (revert 007693f2a3), and have 'invalidation_reason
> > text' for both logical and physical slots. So, whenever 'conflicting'
> > is true, one can look at invalidation_reason for the reason for
> > conflict. How does this sound?
> >
>
> So, does this mean that conflicting will only be true for some of the
> reasons (say wal_level_insufficient, rows_removed, wal_removed) and
> logical slots but not for others? I think that will also not eliminate
> the duplicate information as user could have deduced that from single
> column.

So, how about we turn conflict_reason to only report the reasons that
actually cause conflict with recovery for logical slots, something
like below, and then have invalidation_cause as a generic column for
all sorts of invalidation reasons for both logical and physical slots?

ReplicationSlotInvalidationCause cause = slot_contents.data.invalidated;

if (slot_contents.data.database == InvalidOid ||
cause == RS_INVAL_NONE ||
cause != RS_INVAL_HORIZON ||
cause != RS_INVAL_WAL_LEVEL)
{
nulls[i++] = true;
}
else
{
Assert(cause == RS_INVAL_HORIZON || cause == RS_INVAL_WAL_LEVEL);

values[i++] = CStringGetTextDatum(SlotInvalidationCauses[cause]);
}

--
Bharath Rupireddy
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com