Thread

Re: [PATCH] Expose checkpoint timestamp and duration in pg_stat_checkpointer

Soumya S Murali <soumyamurali.work@gmail.com> — 2025-12-01T05:35:19Z

Hi all,

> On Fri, Nov 28, 2025 at 10:23:54AM +0530, Soumya S Murali wrote:
> > I have updated the code based on the feedback received to my earlier
> > mails and prepared a patch for further review.
>
> I think the logging change and the pg_stat_checkpointer changes are
> different enough that they should be separate patches. If not just
> because the logging change seems to not have had any non-positive
> feedback.

Thank you for the review and for the clarification. I understand the
point about separating the logging change and the pg_stat_checkpointer
additions. As per the suggestion, I will make sure to split them into
two independent patches before sending the updated one.

> > In this patch, I have renamed the checkpoint_total_time to
> > last_checkpoint_duration, stats_reset has been kept as the last column
> > following the usual pattern, last_checkpoint_duration and
> > last_checkpoint_time will now be overwritten per checkpoint and also
> > have removed unnecessary lines as per the usual format. I had
> > successfully verified the checkpointer duration with different write
> > loads and I am  attaching the observations for further reference.
>
> I am still not convinced of the usefulness of those changes to
> pg_stat_checkpointer, but some feedback on the patch:

According to my understanding, The monitoring systems can already poll
pg_stat_checkpointer at a reasonable frequency but with the checkpoint
duration values exposed, I think it will be easier to compute - the
checkpoint deltas, fluctuations in duration, notice unusualities and
the timing instabilities in WAL-driven checkpoints etc. These may seem
simple but are useful signals that many existing monitoring dashboards
lack today.

> diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
> index 9217508917..4a45f4f708 100644
> --- a/src/backend/access/transam/xlog.c
> +++ b/src/backend/access/transam/xlog.c
> @@ -6778,7 +6778,7 @@ LogCheckpointEnd(bool restartpoint, int flags)
>
>
>         /* Store in PendingCheckpointerStats */
> -       PendingCheckpointerStats.checkpoint_total_time += (double) total_msecs;
> +       PendingCheckpointerStats.last_checkpoint_duration = (double) total_msecs;
>         PendingCheckpointerStats.last_checkpoint_time = CheckpointStats.ckpt_end_t;
>
> [...]
>
> diff --git a/src/include/pgstat.h b/src/include/pgstat.h
> index a8eb1f8add..73688041c8 100644
> --- a/src/include/pgstat.h
> +++ b/src/include/pgstat.h
> @@ -263,7 +263,7 @@ typedef struct PgStat_CheckpointerStats
>         PgStat_Counter sync_time;
>         PgStat_Counter buffers_written;
>         PgStat_Counter slru_written;
> -       PgStat_Counter checkpoint_total_time;  /* new: total ms of last checkpoint */
> +       PgStat_Counter last_checkpoint_duration;  /* new: total ms of last checkpoint */
>         TimestampTz    last_checkpoint_time;   /* new: end time of last checkpoint */
>         TimestampTz    stat_reset_timestamp;
>  } PgStat_CheckpointerStats;
>
> This looks like an incremental patch based on your original one? It is
> customary to send the full, updated, patch again.
>
>
> Michael

Ok noted. I will resend a full updated patch set soon and will make
sure every updation goes as per the intended flow.
Thank you for the guidance. Looking forward to more feedback.

Regards,
Soumya