Wow Michael you are absolutely right. Turning jit off results in a query execution about twice as fast as pg11. That is a huge relief. I will read the jit related docs and see if there is anything smarter I should be doing other than disabling jit entirely, but it works a treat for this query.
Regards
Bob
On Wed, 31 May 2023 at 11:11, Michael Christofides <michael@xxxxxxxxxxxxx> wrote:
Does anyone have a theory of why pg15 should behave so differently to pg11 here? Better still, any suggestions for configuration that might make pg15 behave more like pg10. I am really dreading the prospect of stepping our many live implementations back to pg11 :-(.One major factor here appears to be JIT compilation, which is off by default in pg11, but on by default in pg12+.
You can see at the bottom of your slowest query plan that about 233s of the 240s are JIT related.
There is good info in the docs about tuning, or turning off, JIT: https://www.postgresql.org/docs/current/jit-decision.html
