On Tue, Aug 22, 2023 at 2:56 PM Ashutosh Bapat <ashutosh.bapat....@gmail.com> wrote: > > On Tue, Aug 22, 2023 at 9:48 AM Amit Kapila <amit.kapil...@gmail.com> wrote: > > > > > > Another idea is to record the confirm_flush_lsn at the time of > > > persisting the slot. We can use it in two different ways 1. to mark a > > > slot dirty and persist if the last confirm_flush_lsn when slot was > > > persisted was too far from the current confirm_flush_lsn of the slot. > > > 2. at shutdown checkpoint, persist all the slots which have these two > > > confirm_flush_lsns different. > > > > > > > I think using it in the second (2) way sounds advantageous as compared > > to storing another dirty flag because this requires us to update > > last_persisted_confirm_flush_lsn only while writing the slot info. > > OTOH, having a flag dirty_for_shutdown_checkpoint will require us to > > update it each time we update confirm_flush_lsn under spinlock at > > multiple places. But, I don't see the need of doing what you proposed > > in (1) as the use case for it is very minor, basically this may > > sometimes help us to avoid decoding after crash recovery. > > Once we have last_persisted_confirm_flush_lsn, (1) is just an > optimization on top of that. With that we take the opportunity to > persist confirmed_flush_lsn which is much farther than the current > persisted value and thus improving chances of updating restart_lsn and > catalog_xmin faster after a WAL sender restart. We need to keep that > in mind when implementing (2). The problem is if we don't implement > (1) right now, we might just forget to do that small incremental > change in future. My preference is 1. Do both (1) and (2) together 2. > Do (2) first and then (1) as a separate commit. 3. Just implement (2) > if we don't have time at all for first two options. >
I prefer one of (2) or (3). Anyway, it is better to do that optimization (persist confirm_flush_lsn at a regular interval) as a separate patch as we need to test and prove its value separately. -- With Regards, Amit Kapila.
