Re: For loop execution times in PostgreSQL 12 vs 15

Hi

pá 10. 2. 2023 v 19:53 odesílatel Adithya Kumaranchath <
akumaranchath(at)live(dot)com> napsal:

> Hi all,
>
> I am running a simple test and am curious to know why a difference in
> execution times between PostgreSQL 12 vs PostgreSQL 15.
>
> *I have this function:*
> CREATE function test() returns int language plpgsql as $$
> declare
> v_number bigint;
> v_multiplier float = 3.14159;
> loop_cnt bigint;
> begin
>
> for loop_cnt in 1..1000000000
> loop
> v_number := 1000;
> v_number := v_number * v_multiplier;
> end loop;
>
> return 0;
>
> end;$$;
>
> *I execute this in PostgreSQL 12:*
>
>
>
>
> *PostgreSQL 15:*
>
>
> It is much faster in 15 than in 12, and while I love the performance
> improvement. I am curious to know the rationale behind this improvement on
> PostgreSQL 15.
>
> The test result is from PostgreSQL on Windows but I observed the same
> behavior on Linux OS too.
>
> *Server Spec:*
> Intel i7-8650U CPU @1.90GHz 2.11GHz
> RAM 16 GB
> Windows 11 Enterprise
>
> Thanks,
> Adi
>

Please, don't send screenshots - we believe you :-)

Your code can be little bit faster if you use flag IMMUTABLE

There were more patches that reduced the overhead of expression's
evaluation in PL/pgSQL.

History
https://github.com/postgres/postgres/commits/master/src/pl/plpgsql/src/pl_exec.c

Some interesting commits
https://github.com/postgres/postgres/commit/8f59f6b9c0376173a072e4fb7de1edd6a26e6b52
https://github.com/postgres/postgres/commit/fbc7a716084ebccd2a996cc415187c269ea54b3e
https://github.com/postgres/postgres/commit/73b06cf893c9d3bb38c11878a12cc29407e78b6c

Originally, PL/pgSQL was designed as glue of SQL and the expression
evaluation was not too good. It was significantly slower in expression's
evaluation than other interpreters like Perl or Python.

But lot of people uses PL/pgSQL for numeric calculations with PostGIS, so
speed of expression's evaluation is more important than before, and after
all optimizations, although the PL/pgSQL is still slower than generic
interprets - still PL/pgSQL should be used mainly like glue of SQL, the
difference is significantly less - from 10x times slower to 2 slower. Still
there is not any JIT - so the performance is almost good I think.

Regards

Pavel