On Tue, Feb 27, 2024 at 4:49 PM Давыдов Виталий <v.davy...@postgrespro.ru> wrote: > > Thank you for your interest in the discussion! > > On Monday, February 26, 2024 16:24 MSK, Amit Kapila <amit.kapil...@gmail.com> > wrote: > > > I think the reason is probably that when the WAL record for prepared is > already flushed then what will be the idea of async commit here? > > I think, the idea of async commit should be applied for both transactions: > PREPARE and COMMIT PREPARED, which are actually two separate local > transactions. For both these transactions we may call XLogSetAsyncXactLSN on > commit instead of XLogFlush when async commit is enabled. When I use async > commit, I mean to apply async commit to local transactions, not to a twophase > (prepared) transaction itself. > > > At commit prepared, it seems we read prepare's WAL record, right? If so, it > is not clear to me do you see a problem with a flush of commit_prepared or > reading WAL for prepared or both of these. > > The problem with reading WAL is due to async commit of PREPARE TRANSACTION > which saves 2PC in the WAL. At the moment of COMMIT PREPARED the WAL with > PREPARE TRANSACTION 2PC state may not be XLogFlush-ed yet. >
As we do XLogFlush() at the time of prepare then why it is not available? OR are you talking about this state after your idea/patch where you are trying to make both Prepare and Commit_prepared records async? So, PREPARE TRANSACTION should wait until its 2PC state is flushed. > > I did some experiments with saving 2PC state in the local memory of logical > replication worker and, I think, it worked and demonstrated much better > performance. Logical replication worker utilized up to 100% CPU. I'm just > concerned about possible problems with async commit for twophase transactions. > > To be more specific, I've attached a patch to support async commit for > twophase. It is not the final patch but it is presented only for discussion > purposes. There were some attempts to save 2PC in memory in past but it was > rejected. > It would be good if you could link those threads. -- With Regards, Amit Kapila.
