Re[4]: Postgresql planning time too high

["Sterpu Victor" <victor@xxxxxxxx>]

I did some testing and the results are surprising.

I did 3 tests:

	Test 1	Test 2	Test 3
Test conditions	SHOW geqo: "on" SHOW geqo_threshold: "5"	SHOW geqo: "on" SHOW geqo_threshold: "12"	SHOW geqo: "off"
Planning Time	43691.910 ms	5114.959 ms	7305.504 ms
Execution Time	4.002 ms	3.987 ms	5.034 ms

This are things that are way over my knowledge, I can only speculate about this: in the documentation from here geqo_threshold is defined as the number of joins after wich postgres will start to use the generic planner.

On my query there are  about 50 joins so test 1 and test 2 should both be done with the generic planner but the planning time of these tests sugest that this is not the case.

So I think test 1 is generic and test 2 and 3 are deterministic(test 3 can be only deterministic as as setted this way the postgres server).

Anyway, in the end the deterministic planner is much more effective at planning this query that the generic one(test 3 is with generic planner turned off).

------ Original Message ------

From: "Pavel Stehule" <pavel.stehule@xxxxxxxxx>

To: "Sterpu Victor" <victor@xxxxxxxx>

Cc: "Fırat Güleç" <firat.gulec@xxxxxxxxxxxx>; "Pgsql Performance" <pgsql-performance@xxxxxxxxxxxxxxxxxxxx>

Sent: 2019-11-22 2:59:11 PM

Subject: Re: Re[2]: Postgresql planning time too high

pá 22. 11. 2019 v 12:46 odesílatel Sterpu Victor <victor@xxxxxxxx> napsal:

No rows should be returned, DB is empty.

I'm testing now on a empty DB trying to find out how to improve this.

In this query I have 3 joins like this: 

SELECT t1.id, t2.valid_from

FROM t1

JOIN t2 ON (t1.id_t1 = t1.id)

LEFT JOIN t3 ON (t3.id_t1 = t1.id AND t3.valid_from<t2.valid_from)

WHERE t3.id IS NULL

If I delete these 3 joins than the planning time goes down from 5.482 ms to 754.708 ms but I'm not sure why this context is so demanding on the planner.

I'm tryng now to make a materialized view that will allow me to stop using the syntax above.

This query is little bit crazy - it has more than 40 joins - but 700ms for planning is looks too much. Maybe your comp has slow CPU.

Postgres has two planners - deterministic and genetic

  https://www.postgresql.org/docs/9.1/geqo-pg-intro.html

Probably slow plan is related to deterministic planner.

I reattached the same files, they should be fine like this.

------ Original Message ------

From: "Fırat Güleç" <firat.gulec@xxxxxxxxxxxx>

To: "Sterpu Victor" <victor@xxxxxxxx>

Cc: pgsql-performance@xxxxxxxxxxxxxxxxxxxx

Sent: 2019-11-22 1:35:15 PM

Subject: RE: Postgresql planning time too high

Hello Sterpu,

 

First, please run vaccum for your Postgresql DB.

 

No rows returned from your query. Could you double check your query criteria.

 

After that could you send explain analyze again .

 

Regards,

 

FIRAT GÜLEÇ 
Infrastructure & Database Operations Manager
firat.gulec@xxxxxxxxxxxx

 

M: 0 532 210 57 18 
İnönü Mh. Mimar Sinan Cd. No:3 Güzeller Org.San.Bölg. GEBZE / KOCAELİ

 

 

 

From: Sterpu Victor <victor@xxxxxxxx>
Sent: Friday, November 22, 2019 2:21 PM
To: pgsql-performance@xxxxxxxxxxxxxxxxxxxx
Subject: Postgresql planning time too high

 

Hello

 

I'm on a PostgreSQL 12.1 and I just restored a database from a backup.

When I run a query I get a big execution time: 5.482 ms

After running EXPLAIN ANALYZE I can see that the "Planning Time: 5165.742 ms" and the "Execution Time: 6.244 ms".

The database is new(no need to vacuum) and i'm the only one connected to it. I use a single partition on the harddrive.

I also tried this on a postgresql 9.5 and the result was the same.

I'm not sure what to do to improve this situation.

The query and the explain is attached.

 

Thank you