Re: per backend WAL statistics

From: Bertrand Drouvot <bertranddrouvot(dot)pg(at)gmail(dot)com>
To: Michael Paquier <michael(at)paquier(dot)xyz>
Cc: pgsql-hackers(at)lists(dot)postgresql(dot)org
Subject: Re: per backend WAL statistics
Date: 2025-01-09 07:05:54
Message-ID: Z391UplSgYDemTy+@ip-10-97-1-34.eu-west-3.compute.internal
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Hi,

On Thu, Jan 09, 2025 at 01:03:15PM +0900, Michael Paquier wrote:
> On Wed, Jan 08, 2025 at 11:11:59AM +0000, Bertrand Drouvot wrote:
> > Yeah, that's more elegant as it also means that the main callback will not change
> > (should we add even more stats in the future). Done that way in v2 attached.
>
> I've put my hands on v2-0002 to begin with something.
>
> +/* flag bits for different types of statistics to flush */
> +#define PGSTAT_FLUSH_IO (1 << 0) /* Flush I/O statistics */
> +#define PGSTAT_FLUSH_ALL (PGSTAT_FLUSH_IO)
>
> These are located and used only in pgstat_backend.c. It seems to me
> that we'd better declare them in pgstat_internal.h and extend the
> existing pgstat_flush_backend() with an argument so as callers can do
> what they want.
>
> + /* Get our own entry_ref if not provided */
> + if (!entry_ref)
> + entry_ref = pgstat_get_entry_ref(PGSTAT_KIND_BACKEND, InvalidOid,
> + MyProcNumber, false, NULL);
>
> This relates to the previous remark, actually, where I think that it
> is cleaner to have pgstat_flush_backend() do pgstat_get_entry_ref(),
> same way as HEAD, and just pass down the flags.

I see, so you keep pgstat_flush_backend() calls (with an extra arg) and remove
the new "pgstat_backend_flush_io()" function.

> This comes at the cost of pgstat_flush_backend_entry()
> requiring an extra pgstat_tracks_backend_bktype(), which is not a big
> issue, and the patch gets a bit shorter.

Yeah, all of the above is fine by me.

PFA v3 which is v2 refactoring with your proposed above changes.

Regards,

--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com

Attachment Content-Type Size
v3-0001-Extract-logic-filling-pg_stat_get_wal-s-tuple-int.patch text/x-diff 3.9 KB
v3-0002-PGSTAT_KIND_BACKEND-code-refactoring.patch text/x-diff 9.7 KB
v3-0003-per-backend-WAL-statistics.patch text/x-diff 22.0 KB

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