Re: Inconsitancies in pg_stat_bgwriter and pg_stat_database returned values

On Wed, 16 Sep 2020 17:06:45 +0200 (CEST)
RECHTÉ Marc <marc(dot)rechte(at)meteo(dot)fr> wrote:

> Hello,
>
> On one particular PG12.3 instance (same behaviour with PG12.4) we are
> experimenting occasional strange values in the above tables.
>
> For instance looping (10s. period) over this request:
>
> SELECT current_timestamp, checkpoints_timed,
> checkpoints_req,
> checkpoint_write_time,
> checkpoint_sync_time,
> buffers_checkpoint,
> buffers_clean,
> maxwritten_clean,
> buffers_backend,
> buffers_backend_fsync,
> buffers_alloc
> FROM pg_stat_bgwriter
>
> Gives: [...]
>
> One can see that some columns that are supposed to increase only are not
> always. For instance checkpoints_timed suddenly jumps from 438 to 3291, then
> back to 438.
>
> We experiment the same issue in pg_stat_database.

The full row are different in your example, not just a few fields. It looks
like mixed values from different instance.

Could you share some more informations about the context and how to reproduce
it?

Regards,