On Mon, Jun 20, 2022 at 10:38 PM Fabio Pardi <f.pardi@portavita.eu> wrote:
> Just to make sure we are on the same page: every parallel 'CREATE INDEX' writes to temp files, ok.
Yes.
> But why the temp files are always on disk and not in RAM as other operations do?
Why not?
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.
> In the case where there is amble maintenance_work_mem, all writes to
> and reads from temp files will be sequential.
Yes.
--
Peter Geoghegan