On Mon, May 08, 2017 at 10:12:18AM -0700, Paul A Jungwirth wrote:
> I'm working on a problem where partitioning seems to be the right
> approach, but we would need a lot of partitions (say 10k or 100k).
> Everywhere I read that after ~100 child tables you experience
> problems. I have a few questions about that:
We use partitioning, previously one child per month (with history of 1-6
years); I tried using one child per day, and caused issues.
For us, planning time is pretty unimportant (~1sec would be acceptable 99% of
the time) but I recall seeing even more than that. I changed to using daily
granularity for only our largest tables, which seems to be working fine for the
last ~9months. So the issue isn't just "number of children" but "total number
of tables". I believe the problem may have been due to large
pg_statistic/pg_attribute and similar tables taking more than a few 100MBs, and
potentially no longer fitting in buffer cache.
> 3. Is it true that query planning time should scale linearly as I add
> more child tables?
I believe it's understood to be super-linear:
https://www.postgresql.org/message-id/26761.1483989025%40sss.pgh.pa.us
https://www.postgresql.org/message-id/4188.1298960419%40sss.pgh.pa.us
Justin