Re: parallel index creation: maintenance_work_mem not honored? - Mailing list pgsql-admin

Hi all,

Not quite following this line of logic...  If "External sorts are often faster than internal sorts", why bother with increasing work_mem to avoid sorting on disk?

Regards,
Michael Vitale

Fabio Pardi wrote on 6/22/2022 2:15 AM:

Thanks for the clarification Peter,

On 21/06/2022 08:46, Peter Geoghegan wrote:

But why the temp files are always on disk and not in RAM as other operations do?

Why not?

Systems running on slow disks will probably suffer from workers writing temp files to disk.

It is probably true that it would be better to use shared memory in
the case where there is sufficient memory, but it's not all that
significant compared to everything else that must happen at the same
time. It's rarely the bottleneck. External sorts are often faster than
internal sorts. That happens because they can be more CPU cache
friendly, for reasons that aren't fundamental.

I would expect this behavior to be mentioned in the documentation.




regards,

fabio pardi

Regards,

Michael Vitale

Michaeldba@sqlexec.com

703-600-9343