Re: 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