Thread: BUG #18694: DISCARD ALL does not reset execution counters for plpgsql functions
BUG #18694: DISCARD ALL does not reset execution counters for plpgsql functions
From
PG Bug reporting form
Date:
The following bug has been logged on the website: Bug reference: 18694 Logged by: David Pavlíček Email address: pavlicek.david@gmail.com PostgreSQL version: 13.13 Operating system: Linux Description: Recently, I encountered a issue where execution plans for SQL queries within plpgsql functions differed significantly in a pooled database session, even though after each call the session state was cleared using the DISCARD ALL command. As per documentation, DISCARD ALL resets the session to its initial state, which is probably not true for plpgsql exec counters. When considering that execution plans for internal queries is generated based on number of execution within single session (custom vs generic), this can have huge impact on how the functions behaves in combination with connection pooler, whether central one like pgbouncer or those built into client libraries. In my opinion, the DISCARD ALL command should reset the internal execution counters of plpgsql functions.
Re: BUG #18694: DISCARD ALL does not reset execution counters for plpgsql functions
From
"David G. Johnston"
Date:
On Thursday, November 7, 2024, PG Bug reporting form <noreply@postgresql.org> wrote:
The following bug has been logged on the website:
Bug reference: 18694
Logged by: David Pavlíček
Email address: pavlicek.david@gmail.com
PostgreSQL version: 13.13
Operating system: Linux
Description:
In my opinion, the DISCARD ALL command should reset the internal
execution counters of plpgsql functions.
To my knowledge there is no user-exposed way to reset those counters. Thus discard all cannot reset them. It is a missing feature, not a bug. One that I agree makes sense to add.
David J.
Re: BUG #18694: DISCARD ALL does not reset execution counters for plpgsql functions
From
David Pavlíček
Date:
In my opinion it is a bug. Documentation clearly states that DISCARD ALL "resets the session to its initial state", which is not true. So either it's a documentation error and DISCARD ALL isn't meant to completely reset the state, or it's meant to completely reset the state and then it's a bug in its implementation (whether it is a missing feature or bug in existing one). I agree that Implementing a new user-exposed command and then calling it within DISCARD ALL is probably the right solution to the problem.
David P.
čt 7. 11. 2024 v 14:38 odesílatel David G. Johnston <david.g.johnston@gmail.com> napsal:
On Thursday, November 7, 2024, PG Bug reporting form <noreply@postgresql.org> wrote:The following bug has been logged on the website:
Bug reference: 18694
Logged by: David Pavlíček
Email address: pavlicek.david@gmail.com
PostgreSQL version: 13.13
Operating system: Linux
Description:
In my opinion, the DISCARD ALL command should reset the internal
execution counters of plpgsql functions.To my knowledge there is no user-exposed way to reset those counters. Thus discard all cannot reset them. It is a missing feature, not a bug. One that I agree makes sense to add.David J.
Re: BUG #18694: DISCARD ALL does not reset execution counters for plpgsql functions
From
Pavel Stehule
Date:
Hi
pá 8. 11. 2024 v 10:27 odesílatel David Pavlíček <pavlicek.david@gmail.com> napsal:
In my opinion it is a bug. Documentation clearly states that DISCARD ALL "resets the session to its initial state", which is not true. So either it's a documentation error and DISCARD ALL isn't meant to completely reset the state, or it's meant to completely reset the state and then it's a bug in its implementation (whether it is a missing feature or bug in existing one). I agree that Implementing a new user-exposed command and then calling it within DISCARD ALL is probably the right solution to the problem.
Please, don't send the top posting style https://en.wikipedia.org/wiki/Posting_style in this mailing list.
Generally inside Postgres are more internal counters that ensure some unique numbers or names, that are not reset by DISCARD ALL. DISCARD ALL is synonym for
CLOSE ALL; SET SESSION AUTHORIZATION DEFAULT; RESET ALL; DEALLOCATE ALL; UNLISTEN *; SELECT pg_advisory_unlock_all(); DISCARD PLANS; DISCARD TEMP; DISCARD SEQUENCES;
other features not promised. It is hard to say if unique numbers should be resetted too. There are two reasons - possibly performance impact, and it can be hard to implement it. There is not any list of these counters (some counters are inside extensions). It can be better explained in doc.
Regards
Pavel
David P.čt 7. 11. 2024 v 14:38 odesílatel David G. Johnston <david.g.johnston@gmail.com> napsal:On Thursday, November 7, 2024, PG Bug reporting form <noreply@postgresql.org> wrote:The following bug has been logged on the website:
Bug reference: 18694
Logged by: David Pavlíček
Email address: pavlicek.david@gmail.com
PostgreSQL version: 13.13
Operating system: Linux
Description:
In my opinion, the DISCARD ALL command should reset the internal
execution counters of plpgsql functions.To my knowledge there is no user-exposed way to reset those counters. Thus discard all cannot reset them. It is a missing feature, not a bug. One that I agree makes sense to add.David J.