Re: Implement waiting for wal lsn replay: reloaded

On Wed, Nov 5, 2025 at 4:03 PM Xuneng Zhou <xunengzhou(at)gmail(dot)com> wrote:
>
> On Wed, Nov 5, 2025 at 5:51 PM Alexander Korotkov <aekorotkov(at)gmail(dot)com> wrote:
> > On Mon, Nov 3, 2025 at 5:13 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
> > > On 2025-11-03 16:06:58 +0100, Álvaro Herrera wrote:
> > > > On 2025-Nov-03, Alexander Korotkov wrote:
> > > >
> > > > > I'd like to give this subject another chance for pg19. I'm going to
> > > > > push this if no objections.
> > > >
> > > > Sure. I don't understand why patches 0002 and 0003 are separate though.
> > >
> > > FWIW, I appreciate such splits. Even if the functionality isn't usable
> > > independently, it's still different type of code that's affected. And the
> > > patches are each big enough to make that worthwhile for easier review.
> >
> > Thank you for the feedback, pushed.
>
> Thanks for pushing them!
>
> > > One thing that'd be nice to do once we have WAIT FOR is to make the common
> > > case of wait_for_catchup() use this facility, instead of polling...
> >
> > The draft patch for that is attached. WAIT FOR doesn't handle all the
> > possible use cases of wait_for_catchup(), but I've added usage when
> > it's appropriate.
>
> Interesting, could this approach be extended to the flush and other
> modes as well? I might need to spend some time to understand it before
> I can provide a meaningful review.

I think we might end up extending WaitLSNType enum. However, I hate
inHeap and heapNode arrays growing in WaitLSNProcInfo as they are
allocated per process. I found that we could optimize WaitLSNProcInfo
struct turning them into simple variables because a single process can
wait only for a single LSN at a time. Please, check the attached
patch.

------
Regards,
Alexander Korotkov
Supabase