Re: [EXTERNAL] Re: Performance down with JDBC 42

On Mon, 6 Nov 2023 at 08:37, Abraham, Danny <danny_abraham(at)bmc(dot)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