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

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?

Regards,

--
Fujii Masao