Horton

Re: repeated decoding of prepared transactions

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>, Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>, Markus Wanner <markus.wanner@enterprisedb.com>, pgsql-hackers <pgsql-hackers@postgresql.org>, Ajin Cherian <itsajin@gmail.com>, Simon Riggs <simon@enterprisedb.com>, Petr Jelinek <petr.jelinek@enterprisedb.com>
Date: 2021-02-09T18:38:15Z
Lists: pgsql-hackers 
On Tue, Feb 9, 2021 at 6:57 AM Amit Kapila <amit.kapila16@gmail.com> wrote:
> I think similar happens without any of the work done in PG-14 as well
> if we restart the apply worker before the commit completes on the
> subscriber. After the restart, we will send the start_decoding_at
> point based on some previous commit which will make publisher send the
> entire transaction again. I don't think restart of WAL sender or WAL
> receiver is such a common thing. It can only happen due to some bug in
> code or user wishes to stop the nodes or some crash happened.

Really? My impression is that the logical replication protocol is
supposed to be designed in such a way that once a transaction is
successfully confirmed, it won't be sent again. Now if something is
not confirmed then it has to be sent again. But if it is confirmed
then it shouldn't happen.

-- 
Robert Haas
EDB: http://www.enterprisedb.com

Commits

  1. Add option to enable two_phase commits via pg_create_logical_replication_slot.

  2. Avoid repeated decoding of prepared transactions after a restart.

  3. Allow decoding at prepare time in ReorderBuffer.