On Mon, Jan 13, 2025 at 1:31 AM Ashutosh Bapat <ashutosh.bapat....@gmail.com> wrote: > > On Mon, Jan 13, 2025 at 2:52 PM vignesh C <vignes...@gmail.com> wrote: > > > > I felt that the only disadvantage with this approach is that we > > currently wait for all in-progress transactions to complete before > > enabling logical decoding. If a long-running transaction exists and > > the session enabling logical decoding fails—due to factors like > > statement_timeout, transaction_timeout, > > idle_in_transaction_session_timeout, idle_session_timeout, or any > > other failure. This would require restarting the wait. During this > > time, there's a risk that a new long-running transaction could start, > > further delaying the process. Probably this could be solved if the > > waiting is done from any of the background processes through > > PGC_SIGHUP. While this type of failure is likely rare, I’m unsure > > whether we should consider this scenario. > > A related question: While the operation is waiting for already running > transactions to end, the backends whose transactions have finished may > start new transactions. When we switch WAL from 'replica' to > 'logical', there may be some transactions running. Will this lead to > WAL stream with mixes WAL records - some with logical information and > some without?
Yes. There could be mixed WAL records until all running transactions complete. > Do we need to adjust logical decoding to tackle this > situation? Is there a chance that some WAL from same transaction have > logical information and some do not? In the current approach, we first enable logical info WAL-logging to let newly started transactions do logical info WAL-logging, then allow the logical decoding only after all running transactions complete. Therefore, at the time when we allow the logical decoding, all WAL records are written with logical information. Regards, -- Masahiko Sawada Amazon Web Services: https://aws.amazon.com
