From: | "Pavel Stehule" <pavel(dot)stehule(at)gmail(dot)com> |
---|---|
To: | "Bruce Momjian" <bruce(at)momjian(dot)us> |
Cc: | PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: some points for FAQ |
Date: | 2007-10-09 21:36:28 |
Message-ID: | 162867790710091436l601838e6v2bf96216528a9f60@mail.gmail.com |
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Thread: | |
Lists: | pgsql-hackers |
> > >
> >
> > ok. I accept it. Can be some note there? Not this strange select.
>
> Well, with 8.3 having this be faster I am thinking we should wait to see
> if the hacks are needed.
>
difference, on 10K lines (on small think table)
postgres=# select * from test where i = any(array(select
(random()*10000)::int from generate_series(1,20))) limit 1;
i | v
-----+-----
869 | 113
(1 row)
Time: 3,984 ms
postgres=# select * from test order by random() limit 1;
i | v
------+-----
3687 | 293
(1 row)
Time: 21,978 ms
8.2
postgres=# select * from test order by random() limit 1;
i | v
------+-----
4821 | 608
(1 row)
Time: 51,299 ms
postgres=# select * from test where i = any(array(select
(random()*10000)::int from generate_series(1,20))) limit 1;
i | v
-----+-----
762 | 254
(1 row)
Time: 4,530 ms
Results:
8.3 "fast solution' is 6x faster
8.2 'fast solution' is 11x faster .. it's minimum.
Pavel
for me, it's one from typical beginers mistakes
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