Re: May be BUG. Periodic burst growth of the checkpoint_req counter on replica.

On 2024/03/14 9:19, Alexander Korotkov wrote:
> On Mon, Mar 11, 2024 at 11:48 AM Alexander Korotkov
> <aekorotkov(at)gmail(dot)com> wrote:
>>
>> On Mon, Mar 11, 2024 at 5:43 AM Anton A. Melnikov
>> <a(dot)melnikov(at)postgrespro(dot)ru> wrote:
>>> On 11.03.2024 03:39, Alexander Korotkov wrote:
>>>> Now that we distinguish stats for checkpoints and
>>>> restartpoints, we need to update the docs. Please, check the patch
>>>> attached.
>>>
>>> Maybe bring the pg_stat_get_checkpointer_buffers_written() description in consistent with these changes?
>>> Like that:
>>>
>>> --- a/src/include/catalog/pg_proc.dat
>>> +++ b/src/include/catalog/pg_proc.dat
>>> @@ -5740 +5740 @@
>>> - descr => 'statistics: number of buffers written by the checkpointer',
>>> + descr => 'statistics: number of buffers written during checkpoints and restartpoints',
>>
>> This makes sense. I've included this into the revised patch.
>
> Pushed.

If I understand correctly, restartpoints_timed and restartpoints_done were
separated because a restartpoint can be skipped. restartpoints_timed counts
when a restartpoint is triggered by a timeout, whether it runs or not,
while restartpoints_done only tracks completed restartpoints.

Similarly, I believe checkpoints should be handled the same way.
Checkpoints can also be skipped when the system is idle, but currently,
num_timed counts even the skipped ones, despite its documentation stating
it's the "Number of scheduled checkpoints that have been performed."

Why not separate num_timed into something like checkpoints_timed and
checkpoints_done to reflect these different counters?

Regards,

--
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION