Temporary files usage in explain

[Matteo Bonardi]

Hi everybody,

I have a query that creates a large number of temporary files, in this
example ~ 45GB.
Looking at the query plan I can't figure out where temporary files are
being generated.

Explain plan: https://explain.depesz.com/s/BXGT

Usually I'm looking for "external merge Disk" to see temp files usage but,
in this case, the only reference to that is 299,368kB in the last but one
node of explain.
Can anyone help me understand where the 45GB are in that explain?

Thanks,
Matteo

Re: Temporary files usage in explain

[Matteo Bonardi]

Okay, I had a misconception of the buffers option.
As I reread the documentation, I realized how stupid the question was.

I confirm that with the buffers option I now see:

Buffers: shared hit=9617011 read=1328356 dirtied=793 written=397, temp
read=2996659 written=5956399


Thank you both,
Matteo


Il giorno mar 27 apr 2021 alle ore 11:38 David Rowley 
ha scritto:

> On Tue, 27 Apr 2021 at 21:15, Matteo Bonardi  wrote:
> > Explain plan: https://explain.depesz.com/s/BXGT
> >
> > Usually I'm looking for "external merge Disk" to see temp files usage
> but, in this case, the only reference to that is 299,368kB in the last but
> one node of explain.
> > Can anyone help me understand where the 45GB are in that explain?
>
> If you do EXPLAIN (ANALYZE, BUFFERS) you might find that the recursive
> CTE is writing the rest of them out.  Something like "temp written =
> ", likely around 5 million or so, I imagine.
>
> David
>