Re: shared buffers

Sorry,

'someone' launches some kind of batches without telling.

Marc MILLAS
Senior Architect
+33607850334
www.mokadb.com

On Fri, Apr 25, 2025 at 3:42 PM Marc Millas <marc(dot)millas(at)mokadb(dot)com> wrote:

> hello,
>
> got something strange to me:
> Same db ie. same data, around 1.2TB,one on pg13, one on pg16
> same 16 GB of shared_buffers,
> I am the single user.
> both have track_io_timing on
>
> on pg13, if I run a big request with explain (analyze,buffers),
> I see around 6 GB read
> if I do rerun the very same request, no more read(s), all data in the
> shared buffers cache. fine
> If I check with pg_buffercache what's in it, I see the biggest tables of
> my request within the biggest users (in number of blocks used). All this is
> fine.
>
> next, if I do the very same on the pg16 machine, whatever the number of
> times I rerun the explain (analyze, buffers) of the same request, each
> time, the explain shows the same volume of reads. again and again.
> If I check with pg_buffercache, the set of objects stay the same, WITHOUT
> the objects of my request, just like if those objects where sticky.
>
> any idea ?
>
> thanks
>
> Marc MILLAS
> Senior Architect
> +33607850334
> www.mokadb.com
>
>