Re: [HACKERS] logical decoding of two-phase transactions

On Tue, Dec 22, 2020 at 2:51 PM Ajin Cherian <itsajin(at)gmail(dot)com> wrote:
>
> On Sat, Dec 19, 2020 at 2:13 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> > Okay, I have changed the rollback_prepare API as discussed above and
> > accordingly handle the case where rollback is received without prepare
> > in apply_handle_rollback_prepared.
>
>
> I have reviewed and tested your new patchset, I agree with all the
> changes that you have made and have tested quite a few scenarios and
> they seem to be working as expected.
> No major comments but some minor observations:
>
> Patch 1:
> logical.c: 984
> Comment should be "rollback prepared" rather than "abort prepared".
>

Agreed.

> Patch 2:
> decode.c: 737: The comments in the header of DecodePrepare seem out of
> place, I think here it should describe what the function does rather
> than what it does not.
>

Hmm, I have written it because it is important to explain the theory
of concurrent aborts as that is not quite obvious. Also, the
functionality is quite similar to DecodeCommit and the comments inside
the function explain clearly if there is any difference so not sure
what additional we can write, do you have any suggestions?

> reorderbuffer.c: 2422: It looks like pg_indent has mangled the
> comments, the numbering is no longer aligned.
>

Yeah, I had also noticed that but not sure if there is a better
alternative because we don't want to change it after each pgindent
run. We might want to use (a), (b) .. notation instead but otherwise,
there is no big problem with how it is.

> Patch 5:
> worker.c: 753: Type: change "dont" to "don't"
>

Okay.

> Patch 6: logicaldecoding.sgml
> logicaldecoding example is no longer correct. This was true prior to
> the changes done to replay prepared transactions after a restart. Now
> the whole transaction will get decoded again after the commit
> prepared.
>
> postgres=# COMMIT PREPARED 'test_prepared1';
> COMMIT PREPARED
> postgres=# select * from
> pg_logical_slot_get_changes('regression_slot', NULL, NULL,
> 'two-phase-commit', '1');
> lsn | xid | data
> -----------+-----+--------------------------------------------
> 0/168A060 | 529 | COMMIT PREPARED 'test_prepared1', txid 529
> (1 row)
>

Agreed.

> Patch 8:
> worker.c: 2798 :
> worker.c: 3445 : disabling two-phase in tablesync worker.
> considering new design of multiple commits in tablesync, do we need
> to disable two-phase in tablesync?
>

No, but let Peter's patch get committed then we can change it.

> Other than this I've noticed a few typos that are not in the patch but
> in the surrounding code.
> logical.c: 1383: Comment should mention stream_commit_cb not stream_abort_cb.
> decode.c: 686 - Extra "it's" here: "because it's it happened"
>

Anything not related to this patch, please post in a separate email.

Can you please update the patch for the points we agreed upon?

--
With Regards,
Amit Kapila.