Re: Fix lag columns in pg_stat_replication not advancing when replay LSN stalls

Hi,

On Wed, Oct 22, 2025 at 10:45 PM Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
>
> On Wed, Oct 22, 2025 at 4:49 PM Xuneng Zhou <xunengzhou(at)gmail(dot)com> wrote:
> > How about something like:
> >
> > /*
> > * Overflow entries for read heads that collide with the write head.
> > *
> > * When the cyclic buffer fills (write head is about to collide with a read
> > * head), we save that read head's current sample here and mark it as using
> > * overflow (read_heads[i] = -1). This allows the write head to continue
> > * advancing while the overflowed mode continues lag computation using the
> > * saved sample.
> > *
> > * Once the standby's reported LSN advances past the overflow entry's LSN,
> > * we transition back to normal buffer-based tracking.
> > */
>
> LGTM. Thanks!
>
> I've created a patch adding your suggested comments (attached).
> Since this is a follow-up to commit 883a95646a8, which was recently applied
> and backpatched to all supported branches, I think we should backpatch
> this one as well. Thought?
>

LGTM. Thanks for the patch!

Best,
Xuneng