Re: Show WAL write and fsync stats in pg_stat_io

Hi,

Thank you for looking into this!

On Sun, 9 Jun 2024 at 18:05, Nitin Jadhav <nitinjadhavpostgres(at)gmail(dot)com> wrote:
>
> > If possible, let's have all the I/O stats (even for WAL) in
> > pg_stat_io. Can't we show the WAL data we get from buffers in the hits
> > column and then have read_bytes or something like that to know the
> > amount of data read?
>
> The ‘hits’ column in ‘pg_stat_io’ is a vital indicator for adjusting a
> database. It signifies the count of cache hits, or in other words, the
> instances where data was located in the ‘shared_buffers’. As a result,
> keeping an eye on the ‘hits’ column in ‘pg_stat_io’ can offer useful
> knowledge about the buffer cache’s efficiency and assist users in
> making educated choices when fine-tuning their database. However, if
> we include the hit count of WAL buffers in this, it may lead to
> misleading interpretations for database tuning. If there’s something
> I’ve overlooked that’s already been discussed, please feel free to
> correct me.

I think counting them as a hit makes sense. We read data from WAL
buffers instead of reading them from disk. And, WAL buffers are stored
in shared memory so I believe they can be counted as hits in the
shared buffers. Could you please explain how this change can 'lead to
misleading interpretations for database tuning' a bit more?

--
Regards,
Nazir Bilal Yavuz
Microsoft