Re: Regex performance issue

I may miss something but I'd use tsearch2. Check
intdict dictionary for basic idea - http://www.sai.msu.su/~megera/wiki/Gendict

Oleg
On Sat, 2 Dec 2006, Alexandru Coseru wrote:

> Hello...
>
> I cannot use LIKE , because the order of the match is reversed.
> The prefix column is containing telephone destinations.
> IE: ^001 - US , ^0039 Italy , etc..
>
> Here is a small sample:
>
> asterisk=> select * from destlist LIMIT 10;
> id | id_ent | dir | prefix | country | network | tip
> ----+--------+-----+------------+-------------+--------------------+-----
> 1 | -1 | 0 | (^0093) | AFGHANISTAN | AFGHANISTAN | 6
> 2 | -1 | 0 | (^00937) | AFGHANISTAN | AFGHANISTAN Mobile | 5
> 3 | -1 | 0 | (^00355) | ALBANIA | ALBANIA | 6
> 4 | -1 | 0 | (^0035538) | ALBANIA | ALBANIA Mobile | 5
> 5 | -1 | 0 | (^0035568) | ALBANIA | ALBANIA Mobile | 5
> 6 | -1 | 0 | (^0035569) | ALBANIA | ALBANIA Mobile | 5
> 7 | -1 | 0 | (^00213) | ALGERIA | ALGERIA | 6
> 8 | -1 | 0 | (^0021361) | ALGERIA | ALGERIA Mobile | 5
> 9 | -1 | 0 | (^0021362) | ALGERIA | ALGERIA Mobile | 5
> 10 | -1 | 0 | (^0021363) | ALGERIA | ALGERIA Mobile | 5
>
>
> Now , I have to match a dialednumber (let's say 00213618833) and find
> it's destination...(It's algeria mobile).
> I tried to make with a query of using LIKE , but i was not able to get
> something..
>
>
> Regards
> Alex
>
>
>
>
>
> ----- Original Message ----- From: "Dave Dutcher" <dave(at)tridecap(dot)com>
> To: "'Alexandru Coseru'" <alexandru(dot)coseru(at)totaltelecom(dot)ro>;
> <pgsql-performance(at)postgresql(dot)org>
> Sent: Saturday, December 02, 2006 10:36 PM
> Subject: RE: [PERFORM] Regex performance issue
>
>
>> -----Original Message-----
>> From: pgsql-performance-owner(at)postgresql(dot)org On Behalf Of Alexandru Coseru
>> asterisk=> explain analyze SELECT * FROM destlist WHERE
>> '0039051248787' ~
>> prefix AND id_ent='-2' AND dir=0 ORDER by length(prefix) DESC;
>>
>>
>> QUERY PLAN
>> --------------------------------------------------------------
>> ----------------------------------------------------------------------
>> Sort (cost=7925.07..7925.15 rows=31 width=67) (actual
>> time=857.715..857.716 rows=2 loops=1)
>> Sort Key: length((prefix)::text)
>> -> Bitmap Heap Scan on destlist (cost=60.16..7924.30
>> rows=31 width=67)
>> (actual time=2.156..857.686 rows=2 loops=1)
>> Recheck Cond: ((id_ent = -2) AND (dir = 0))
>> Filter: ('0039051248787'::text ~ (prefix)::text)
>> -> Bitmap Index Scan on destlist_indx2 (cost=0.00..60.16
>> rows=6193 width=0) (actual time=1.961..1.961 rows=5205 loops=1)
>> Index Cond: ((id_ent = -2) AND (dir = 0))
>> Total runtime: 857.804 ms
>> (8 rows)
>>
>>
>> "mmumu" btree (prefix varchar_pattern_ops)
>>
>
> I'm surpised Postgres isn't using the index on prefix seeing as the index
> uses the varchar_pattern_ops operator class. It could be that the index
> isn't selective enough, or is Postgres not able to use an index with Posix
> regular expressions? The docs seem to say that it can, but I'd be curious
> to see what happens if you use LIKE instead of ~.
>
> Dave
>
>
>
>
>
>

Regards,
Oleg
_____________________________________________________________
Oleg Bartunov, Research Scientist, Head of AstroNet (www.astronet.ru)
Sternberg Astronomical Institute, Moscow University, Russia
Internet: oleg(at)sai(dot)msu(dot)su, http://www.sai.msu.su/~megera/
phone: +007(495)939-16-83, +007(495)939-23-83