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 <mich...@pgmustard.com> 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 >
