Hello Amit, thanks for your very quick response.
On 08.02.21 11:13, Amit Kapila wrote:
/* * It is possible that this transaction is not decoded at prepare time * either because by that time we didn't have a consistent snapshot or it * was decoded earlier but we have restarted. We can't distinguish between * those two cases so we send the prepare in both the cases and let * downstream decide whether to process or skip it. We don't need to * decode the xact for aborts if it is not done already. */
The way I read the surrounding code, the only case a 2PC transaction does not get decoded a prepare time is if the transaction is empty. Or are you aware of any other situation that might currently happen?
(unless the server needs to be restarted due to some reason)
Right, the repetition occurs only after a restart of the walsender in between a prepare and a commit prepared record.
That anyway is true without this work as well where restart_lsn can be advanced on commits. We haven't changed anything in that regard.
I did not mean to blame the patch, but merely try to understand some of the design decisions behind it.
And as I just learned, even if we managed to avoid the repetition, a restarted walsender still needs to see prepared transactions as in-progress in its snapshots. So we cannot move forward the restart_lsn to after a prepare record (until the final commit or rollback is consumed).
Best Regards Markus
