Re: log XLogPrefetch stats at end of recovery

Hi all,

Thank you for your feedback. Please see the attached patch.

On Mon, Mar 23, 2026 at 4:30 AM Jakub Wartak <jakub(dot)wartak(at)enterprisedb(dot)com>
wrote:

> On Sun, Mar 22, 2026 at 1:43 AM Bharath Rupireddy
> <bharath(dot)rupireddyforpostgres(at)gmail(dot)com> wrote:
>
> Hi,
>
> > On Sat, Mar 21, 2026 at 1:16 AM SATYANARAYANA NARLAPURAM
> > <satyanarlapuram(at)gmail(dot)com> wrote:
> > >
> > > > While investigating a long recovery, I noticed that XLogPrefetch
> stats were not logged at the end of recovery. This log message will be
> useful to understand how effective XLogPrefetch was during recovery. Adding
> a patch to address this.
> > >
> > > Applied this patch and validated the log message. This log message
> appears to be useful to me, particularly while doing fleet wide analysis.
> > >
> > > 2026-03-20 23:33:13.756 PDT [2265441] LOG: XLogPrefetcher stats:
> prefetch=14, hit=6, skip_init=5, skip_new=28, skip_fpw=18, skip_rep=996
> >
> > This looks useful to understand how the prefetch helped during long
> recoveries.
> >
> > > I am wondering if we can periodically log this in standby mode as
> well, not just before promoting?
> >
> > Timer-based startup progress messaging allows logging such things
> > (ereport_startup_progress API). There was an attempt to enable "redo
> > in progress" for standbys, but that seemed to flood the standby logs
> > even at the default progress interval of 10 sec.
> >
> > Having said that, the prefetcher stats could be added to the existing
> > ereport_startup_progress("redo in progress xxx") message that works
> > for crash recoveries—however, I don't prefer doing a bunch of atomic
> > reads every progress interval of 10 sec.
>
> > Therefore, logging at the end of recovery looks good to me.
>
> +1 from me too to only of logging at the end of recovery (so -1 to logging
> every now and then). If someone is interested in current state (or progress
> over time) I think he can query pg_stat_recovery_prefetch view already,
> even
> today, right?

> I reviewed the patch. I have the following comment:
> >
> > + elog(LOG, "XLogPrefetcher stats: prefetch=%lu, hit=%lu,
> > skip_init=%lu, skip_new=%lu, skip_fpw=%lu, skip_rep=%lu",
> >
> > XLogPrefetcher is an internal data structure name, how about "redo
> > prefetch stats: xxxx" to be consistent with other redo log messages?
>
> +1
>

please find the attached patch addressing this.

Regards,
Lakshmi