Re: Huge table searching optimization

От: Andres Freund
Тема: Re: Huge table searching optimization
Дата: ,
Msg-id: 201004051810.57673.andres@anarazel.de
(см: обсуждение, исходный текст)
Ответ на: Huge table searching optimization  (Oliver Kindernay)
Ответы: Re: Huge table searching optimization  (Tom Lane)
Список: pgsql-performance

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Huge table searching optimization  (Oliver Kindernay, )
 Re: Huge table searching optimization  (hubert depesz lubaczewski, )
 Re: Huge table searching optimization  (Andres Freund, )
  Re: Huge table searching optimization  (Tom Lane, )
   Re: Huge table searching optimization  (Oliver Kindernay, )

Hi,

On Monday 05 April 2010 16:28:35 Oliver Kindernay wrote:
> Hi, I have table with just on column named url (it's not real url,
> just random string for testing purposes), type text. I have lots of
> entries in it (it's dynamic, i add and remove them on the fly), 100
> 000 and more. I've created index on this table to optimize
> "searching". I just want to test if some "url" is in in the table, so
> i am using this request:
>
> select url from test2 where url ~* '^URLVALUE\\s*$';
>
> there's \\s* because of padding. Here is the analyze:
>
> postgres=# explain analyze select url from test2  where url ~*
> '^zyxel\\s*$'; WARNING:  nonstandard use of \\ in a string literal
> LINE 1: ...plain analyze select url from test2  where url ~* '^zyxel\\s...
>                                                              ^
> HINT:  Use the escape string syntax for backslashes, e.g., E'\\'.
>                                               QUERY PLAN
> ---------------------------------------------------------------------------
> ---------------------------- Seq Scan on test2  (cost=0.00..1726.00 rows=10
> width=9) (actual
> time=156.489..156.502 rows=1 loops=1)
>    Filter: (url ~* '^zyxel\\s*$'::text)
>  Total runtime: 156.538 ms
> (3 rows)
>
> It takes 156 ms, it's too much for my purposes, so i want to decrease
> it. So what can I use for optimizing this request? Again, I just want
> to test if "url" ("zyxel" in this examlpe) is in the table.
>
Depending on your locale it might be sensible to create a text_pattern_ops
index - see the following link:
http://www.postgresql.org/docs/current/static/indexes-opclass.html

Like suggested by depesz it would be far better to remove the padding and do
exact lookups though.

Andres


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