Обсуждение: Temporary Files
PostgreSQL 12
I just increased my work_mem to 24 MB. I cleared my statistics. I then went back later and saw the following:
Temporary files: 21
Size of temporary files 451 MB.
If you divide 451 by 21 you get 21.4 . I would have expected to see an average size greater than 24 MB. This implies to me that PostgreSQL is creating temp files that are smaller than 24 MB.
What am I not understanding?
Thanks,
Software Architect
217.333.0382
Under the Illinois Freedom of Information Act any written communication to or from university employees regarding university business is a public record and may be subject to public disclosure.
Вложения
On Mon, Mar 29, 2021 at 11:10 AM Campbell, Lance <lance@illinois.edu> wrote: > If you divide 451 by 21 you get 21.4 . I would have expected to see an average size greater than 24 MB. This impliesto me that PostgreSQL is creating temp files that are smaller than 24 MB. > > What am I not understanding? work_mem limits the in-memory space used by sort and hash operations. It doesn't necessarily follow that the on-disk footprint is exactly (or even approximately) the same as the in-memory footprint for any given operation that barely can't fit in memory. The precise space overheads will vary based on lots of factors, most of which are implementation details. -- Peter Geoghegan