Re: Invocation overhead for procedural languages

2008/8/6 Giorgio Valoti <giorgio_v(at)mac(dot)com>:
> Hi all, I think I've read somewhere in the documentation that the invocation
> of functions written in procedural languages (with the exception of plpgsql)
> incur in performance hit due to the call the language interpreter. Is that
> correct or am I completely off track?

it's depend. Start of interpret is only one overhead. Other is date
conversions to language compatible types (without C and plpgsql).
Only plpgsql share expression evaluation with database, so it's
specific overhead only for plpgsql.

postgres=# create function testpg(a integer) returns integer as
$$begin return 1; end; $$ language plpgsql immutable;
CREATE FUNCTION
postgres=# create function testperl(a integer) returns integer as
$$return 1;$$ language plperl;
CREATE FUNCTION

postgres=# select sum(testperl(i)) from generate_series(1,10000) g(i);
sum
-------
10000
(1 row)

Time: 588,649 ms
postgres=# select sum(testpg(i)) from generate_series(1,10000) g(i);
sum
-------
10000
(1 row)

Time: 51,214 ms

so in this trivial function is plpgql faster then perl, that is fata morgana :).

first start is diferent:
postgres=# select testpg(1);
testpg
--------
1
(1 row)

Time: 3,409 ms
postgres=# select testperl(1);
testperl
----------
1
(1 row)

Time: 86,199 ms
second is similar
postgres=# select testperl(1);
testperl
----------
1
(1 row)

Time: 1,059 ms
postgres=# select testpg(1);
testpg
--------
1
(1 row)

Time: 0,955 ms

but you can load perl after server start - look on preload_libraries
section in postgresql.conf

regards
Pavel Stehule

>
> Thank you in advance
> --
> Giorgio Valoti
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