Very good point from Danny: generic and custom plans. One thing that is almost certainly not at play here, and is mentioned: there are some specific cases where the planner does not optimise for the query in total to be executed as fast/cheap as possible, but for the first few rows. One reason for that to happen is if a query is used as a cursor.
(Warning: shameless promotion) I did a writeup on JDBC clientside/serverside prepared statements and custom and generic plans: https://dev.to/yugabyte/postgres-query-execution-jdbc-prepared-statements-51e2 The next obvious question then is if something material did change with JDBC for your old and new JDBC versions, I do believe the prepareThreshold did not change. Frits Hoogland > On 5 Nov 2023, at 20:47, David Rowley <dgrowle...@gmail.com> wrote: > > On Mon, 6 Nov 2023 at 08:37, Abraham, Danny <danny_abra...@bmc.com> wrote: >> >> Both plans refer to the same DB. > > JDBC is making use of PREPARE statements, whereas psql, unless you're > using PREPARE is not. > >> #1 – Fast – using psql or old JDBC driver > > The absence of any $1 type parameters here shows that's a custom plan > that's planned specifically using the parameter values given. > >> Slow – when using JDBC 42 > > Because this query has $1, $2, etc, that's a generic plan. When > looking up statistics histogram bounds and MCV slots cannot be > checked. Only ndistinct is used. If you have a skewed dataset, then > this might not be very good. > > You might find things run better if you adjust postgresql.conf and set > plan_cache_mode = force_custom_plan then select pg_reload_conf(); > > Please also check the documentation so that you understand the full > implications for that. > > David > >
