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

Hi,

On Mon, Nov 24, 2025 at 11:40:44AM +0530, Soumya S Murali wrote:
> While debugging checkpointer write behavior, I recently found some of the
> enhancements related to extending pg_stat_checkpointer by including
> checkpoint type (manual/timed/immediate), last_checkpoint_time and
> checkpoint_total_time information to checkpoint completion logs through SQL
> when `log_checkpoints` is enabled. I am attaching my observations,
> screenshots and patch in support for this.
>
> 1. Log for type of checkpoint occured:
>
> 2025-11-20 11:51:06.128 IST [18026] LOG: checkpoint complete
> (immediate): wrote 7286 buffers (44.5%), wrote 4 SLRU buffers; 0 WAL
> file(s) added, 0 removed, 27 recycled; write=0.095 s, sync=0.034 s,
> total=0.279 s; sync files=17, longest=0.004 s, average=0.002 s;
> distance=447382 kB, estimate=531349 kB; lsn=0/7F4EDED8, redo
> lsn=0/7F4EDE80

I think that'd be useful; the checkpoint complete log line clearly has
the more interesting output, and having it state the type would make it
easier to answer question like "how many buffers did the last wal-based
checkpoint write?

> 2. Log for the checkpoint_total_time and last_checkpoint_time:
>
> checkpoint_total_time | last_checkpoint_time
> -----------------------+----------------------------------
> 175138 | 2025-11-20 11:58:02.879149+05:30
> (1 row)

Reading throught the patch, it looks like checkpoint_total_time is the
total time of the last checkpoint?

> + proparallel => 'r', prorettype => 'float8', proargtypes => '',
> + prosrc => 'pg_stat_get_checkpointer_checkpoint_total_time' },

If so, the naming is pretty confusing, last_checkpoint_duration or
something might be clearer.

In general I doubt how much those gauges (as oppposed to counters) only
pertaining to the last checkpoint are useful in pg_stat_checkpointer.
What would be the use case for those two values?

Also, as a nitpick, your patch adds unnecessary newlines and I think
stats_reset should be kept as last column in pg_stat_checkpointer as
usual.

Michael