Re: Implement waiting for wal lsn replay: reloaded

On Sat, Nov 8, 2025 at 12:02 AM Alexander Korotkov <aekorotkov@gmail.com> wrote:
> On Wed, Nov 5, 2025 at 4:03 PM Xuneng Zhou <xunengzhou@gmail.com> wrote:
> > On Wed, Nov 5, 2025 at 5:51 PM Alexander Korotkov <aekorotkov@gmail.com> wrote:
> > > On Mon, Nov 3, 2025 at 5:13 PM Andres Freund <andres@anarazel.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.

Here is the updated patch integrating minor corrections provided by
Xuneng Zhou off-list.  I'm going to push this if no objections.

------
Regards,
Alexander Korotkov
Supabase