From: | Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> |
---|---|
To: | Konstantin Knizhnik <k(dot)knizhnik(at)postgrespro(dot)ru> |
Cc: | "Tsunakawa, Takayuki" <tsunakawa(dot)takay(at)jp(dot)fujitsu(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Why overhead of SPI is so large? |
Date: | 2019-08-23 09:10:28 |
Message-ID: | CAFj8pRC=jQaKYQHRopvZtRKvyEr3uxcdT6PLORDs5o4hMu+Xhw@mail.gmail.com |
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pá 23. 8. 2019 v 11:05 odesílatel Konstantin Knizhnik <
k(dot)knizhnik(at)postgrespro(dot)ru> napsal:
>
>
> On 22.08.2019 18:56, Pavel Stehule wrote:
>
>
>
> čt 22. 8. 2019 v 17:51 odesílatel Konstantin Knizhnik <
> k(dot)knizhnik(at)postgrespro(dot)ru> napsal:
>
>> Some more information...
>> First of all I found out that marking PL/pgSQL function as immutable
>> significantly increase speed of its execution:
>> 19808 ms vs. 27594. It happens because exec_eval_simple_expr is taken
>> snapshot if function is volatile (default).
>> I wonder if PL/pgSQL compiler can detect that evaluated expression itself
>> is actually immutable and there is no need to take snapshot
>> for each invocation of this function. Also I have tried yet another PL
>> language - JavaScript, which is now new outsider, despite to the fact that
>> v8 JIT compiler is very good.
>>
>
> I have a plan to do some work in this direction. Snapshot is not necessary
> for almost buildin functions. If expr calls only buildin functions, then
> probably can be called without snapshot and without any work with plan
> cache.
>
>
> I wonder if the following simple patch is correct?
>
You cannot to believe to user defined functions so immutable flag is
correct. Only buildin functions are 100% correct.
CREATE OR REPLACE FUNCTION foo()
RETURNS int AS $$
SELECT count(*) FROM pg_class;
$$ LANGUAGE sql IMMUTABLE;
is working.
But your patch is good enough for benchmarking.
Pavel
>
> --
> Konstantin Knizhnik
> Postgres Professional: http://www.postgrespro.com
> The Russian Postgres Company
>
>
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