Hello..
I cannot use the first advice , because i'm not aware of the prefix length
in the database...
This is why i'm ordering after length(prefix)..
On the 2nd one , i'm not sure that i can follow you..
Regards
Alex
----- Original Message -----
From: "Heikki Linnakangas" <heikki@xxxxxxxxxxxxxxxx>
To: "Alexandru Coseru" <alexandru.coseru@xxxxxxxxxxxxxxx>
Cc: "Dave Dutcher" <dave@xxxxxxxxxxxx>; <pgsql-performance@xxxxxxxxxxxxxx>
Sent: Sunday, December 03, 2006 12:04 AM
Subject: Re: [PERFORM] Regex performance issue
Alexandru Coseru wrote:
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..
Maybe you could create a functional index on substr(<minimum length of
prefix>)? It might restrict the result set prior to applying the regex
just enough to make the performance acceptable.
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..
Another idea would be to add some extra rows so that you could use normal
inequality searches. For example, let's take the Albanian rows:
3 | -1 | 0 | 00355
4 | -1 | 0 | 0035538
* 3 | -1 | 0 | 0035539
5 | -1 | 0 | 0035568
6 | -1 | 0 | 0035569
* 3 | -1 | 0 | 0035570
Now you can do "SELECT * FROM destlist WHERE ? >= prefix ORDER BY prefix
LIMIT 1".
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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