Re: pg_buffercache: Add per-relation summary stats

Hi Bertrand,

Thanks for your review, and sorry it took me a while to get to it -
other patches took more of my attention unexpectedly.

On Mon, Mar 9, 2026 at 2:15 AM Bertrand Drouvot
<bertranddrouvot(dot)pg(at)gmail(dot)com> wrote:
> === 1
>
> +typedef struct
> +{
> + RelFileNumber relfilenumber;
> + Oid reltablespace;
> + Oid reldatabase;
> + ForkNumber forknum;
> +} BufferRelStatsKey;
>
> What about making use of RelFileLocator (instead of 3 members relfilenumber,
> reltablespace and reldatabase)?

Agreed, and noted by others later too - will adjust.

> + <para>
> + The <function>pg_buffercache_relation_stats()</function> function returns a
> + set of rows summarizing the state of all shared buffers, aggregated by
> + relation and fork number. Similar and more detailed information is
> + provided by the <structname>pg_buffercache</structname> view, but
> + <function>pg_buffercache_relation_stats()</function> is significantly
> + cheaper.
> + </para>
>
> I'm not 100% sure about the name of the function since the stats are "reset"
> after a rewrite. What about pg_buffercache_relfilenode or
> pg_buffercache_aggregated?

I'll gone with "pg_buffercache_relations" for now in v2, but I could
also see "pg_buffercache_relfilenodes" making sense, if we wanted to
be more clear about the fact that these are physical relation files,
not logical relations.

Thanks,
Lukas

--
Lukas Fittl