Re: Notes about Pl/PgSQL assignment performance

Hi

2017-12-19 12:28 GMT+01:00 Андрей Жиденков <pensnarik@gmail.com>:

Few day ago a faced a problem: Pl/PgSQL procedure works slower when running in parallel threads. I found the correlation between number of assignments in procedure code and performance. I decided to write the simple benchmark procedures and perform some test on PostgreSQL 9.6.5 database installed on the server with 20 CPU cores (2 Xeon E5-2690V2 CPUs).

This benchmark showed me that a simple Pl/PgSQL procedure with a simple loop inside works slower when running even in 2 threads. There is a procedure:

CREATE OR REPLACE FUNCTION benchmark_test() RETURNS VOID AS $$

DECLARE

  v INTEGER; i INTEGER;

BEGIN

  for i in 1..1000 loop

    v := 1;

  end loop;

END;

$$ LANGUAGE plpgsql;

What is the point? I know, that Pl/PgSQL performs a SELECT query to calculate each value for assignment but I didn't expect that it produce side effects like this. If there is some buffer lock or anything else?

I am little bit lost when you are speaking about threads. Postgres doesn't use it.

your test is not correct - benchmark_test should be marked as immutable.

What will be result?

Regards

Pavel

 

I've been written a post with charts and detailed explanation to display these side effects: http://telegra.ph/Notes-about-PlPgSQL-assignment-performance-12-19

Any help would be greatly appreciated.

--

-- 
Hannu Krosing
PostgreSQL Consultant
Performance, Scalability and High Availability
https://2ndquadrant.com/