Re: The performance issues caused by upgrading PostgreSQL to version 16.3.

On Mon, Feb 17, 2025 at 2:55 AM 馬 騰飛 <ma-tengfei(at)nec(dot)cn> wrote:

> Dear PostgreSQL Community,
>
> I hope this message finds you well. I am reaching out to seek your
> technical assistance regarding a performance issue we encountered after
> upgrading our PostgreSQL version from 12.19 to 16.3.
> We have noticed a significant performance problem with a specific SQL
> query on one of our application screens.
> Interestingly, when we isolate the problematic SQL statement and replace
> its parameters with actual values, it executes in just a few seconds in
> pgAdmin.
> However, when we run the same SQL query through our application using
> Npgsql, it takes over ten minutes to complete.

We are using NpgsqlCommand.ExecuteReader to execute the SQL query, and the
> parameters are set using NpgsqlCommand.Parameters.Add.
> The main table involved in this query contains approximately 800,000
> records.
> We believe that the SQL statement itself does not have performance issues,
> but there may be problems related to how the SQL is executed in the
> application or how the parameters are set.
> However, we are unable to pinpoint the exact cause of the performance
> degradation.
>

Your situation sounds like something we encountered a few years ago in
PG12. The solution was to add:
set plan_cache_mode = force_custom_plan

This is only for when the first five or six executions of a prepared
statement run fast, and performance drops after that.
Test the query using PREPARE (
https://www.postgresql.org/docs/16/sql-prepare.html) and ten different
parameter sets, with and without "set plan_cache_mode = force_custom_plan".

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