On Thu, Jun 5, 2025 at 4:07 AM Hayato Kuroda (Fujitsu)
<kuroda.hayato@fujitsu.com> wrote:
>
> Dear Amit,
>
> > > ---
> > > I'd like to make it clear again which case we need to execute
> > > txn->invalidations as well as txn->invalidations_distributed (like in
> > > ReorderBufferProcessTXN()) and which case we need to execute only
> > > txn->invalidations (like in ReorderBufferForget() and
> > > ReorderBufferAbort()). I think it might be worth putting some comments
> > > about overall strategy somewhere.
> > >
> > > ---
> > > BTW for back branches, a simple fix without ABI breakage would be to
> > > introduce the RBTXN_INVAL_OVERFLOWED flag to limit the size of
> > > txn->invalidations. That is, we accumulate inval messages both coming
> > > from the current transaction and distributed by other transactions but
> > > once the size reaches the threshold we invalidate all caches. Is it
> > > worth considering for back branches?
> > >
> >
> > It should work and is worth considering. The main concern would be
> > that it will hit sooner than we expect in the field, seeing the recent
> > reports. So, such a change has the potential to degrade the
> > performance. I feel that the number of people impacted due to
> > performance would be more than the number of people impacted due to
> > such an ABI change (adding the new members at the end of
> > ReorderBufferTXN). However, if we think we want to go safe w.r.t
> > extensions that can rely on the sizeof ReorderBufferTXN then your
> > proposal makes sense.
>
> While considering the approach, I found a doubtful point. Consider the below
> workload:
>
> 0. S1: CREATE TABLE d(data text not null);
> 1. S1: BEGIN;
> 2. S1: INSERT INTO d VALUES ('d1')
> 3. S2: BEGIN;
> 4. S2: INSERT INTO d VALUES ('d2')
> 5. S1: ALTER PUBLICATION pb ADD TABLE d;
> 6. S1: ... lots of DDLs so overflow happens
> 7. S1: COMMIT;
> 8. S2: INSERT INTO d VALUES ('d3');
> 9. S2: COMMIT;
> 10. S2: INSERT INTO d VALUES ('d4');
>
> In this case, the inval message generated by step 5 is discarded at step 6. No
> invalidation messages are distributed in the SnapBuildDistributeSnapshotAndInval().
> While decoding S2, relcache cannot be discarded and tuples d3 and d4 won't be
> replicated. Do you think this can happen?
I think that once the S1's inval messages got overflowed, we should
mark other transactions as overflowed instead of distributing inval
messages.
Regards,
--
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com
