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.
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.
On 5 Nov 2023, at 20:47, David Rowley <dgrowleyml@gmail.com> wrote:
On Mon, 6 Nov 2023 at 08:37, Abraham, Danny <danny_abraham@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
