The performance issues caused by upgrading PostgreSQL to version 16.3.

On Mon, 2025-02-17 at 07:55 +0000, 馬　騰飛 wrote:

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.

I recommend using the auto_explain module to capture the plan of the statement
when the application executes it.

You best write the fast and the slow plan to the list, in plain text.

Yours,
Laurenz Albe

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On Mon, Feb 17, 2025 at 2:55 AM 馬 騰飛 <ma-tengfei@nec.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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Don't boil me, I'm still alive.
<Redacted> lobster!

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

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.

Another reason could be a poor type casting by your driver/middleware. Can
you share the query that is problematic? (also, since you mentioned a
version upgrade, also make sure you run ANALYZE; post-upgrade.)

Cheers,
Greg

--
Crunchy Data - https://www.crunchydata.com
Enterprise Postgres Software Products & Tech Support

post installing, did you run analyze verbose?

-Doron

On Mon, Feb 17, 2025 at 4:23 PM Greg Sabino Mullane <htamfids@gmail.com>
wrote:

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

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.

Another reason could be a poor type casting by your driver/middleware. Can
you share the query that is problematic? (also, since you mentioned a
version upgrade, also make sure you run ANALYZE; post-upgrade.)

Cheers,
Greg

--
Crunchy Data - https://www.crunchydata.com
Enterprise Postgres Software Products & Tech Support

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On 2/16/25 23:55, 馬 騰飛 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.
Could you please provide us with some possible reasons or suggestions for improvement? Your insights would be greatly appreciated.

This is going to need more information:

1) Was the upgrade done on the same machine or across machines?
If across machines how are they different?

2) The table definition.

3) The query text.

4) The Npgsql code.

Thank you for your assistance, and I look forward to your response.

Best regards,
Ma

--
Adrian Klaver
adrian.klaver@aklaver.com