Consulta de atualização muito lenta no Postgres 9.1

• dividir os URLs em componentes {protocol,hostname,pathname}.
• Agora você pode usar correspondências exatas para unir a parte do nome do host, evitando o % inicial na regex-match.
• a visualização destina-se a demonstrar que o full_url pode ser reconstruído, se necessário.

SET search_path='tmp';

DROP TABLE urls CASCADE;
CREATE TABLE urls
        ( id SERIAL NOT NULL PRIMARY KEY
        , full_url varchar
        , proto varchar
        , hostname varchar
        , pathname varchar
        );

INSERT INTO urls(full_url) VALUES
 ( 'ftp://www.myhost.com/secret.tgz' )
,( 'http://www.myhost.com/robots.txt' )
,( 'http://www.myhost.com/index.php' )
,( 'https://www.myhost.com/index.php' )
,( 'http://www.myhost.com/subdir/index.php' )
,( 'https://www.myhost.com/subdir/index.php' )
,( 'http://www.hishost.com/index.php' )
,( 'https://www.hishost.com/index.php' )
,( 'http://www.herhost.com/index.php' )
,( 'https://www.herhost.com/index.php' )
        ;

UPDATE urls
SET proto = split_part(full_url, '://' , 1)
        , hostname = split_part(full_url, '://' , 2)
        ;

UPDATE urls
SET pathname = substr(hostname, 1+strpos(hostname, '/' ))
        , hostname = split_part(hostname, '/' , 1)
        ;

        -- the full_url field is now redundant: we can drop it
ALTER TABLE urls
        DROP column full_url
        ;
        -- and we could always reconstruct the full_url from its components.
CREATE VIEW vurls AS (
        SELECT id
        , proto || '://' || hostname || '/' || pathname AS full_url
        , proto
        , hostname
        , pathname
        FROM urls
        );

SELECT * FROM urls;
        ;
SELECT * FROM vurls;
        ;

INSERT 0 10
UPDATE 10
UPDATE 10
ALTER TABLE
CREATE VIEW
 id | proto |    hostname     |     pathname     
----+-------+-----------------+------------------
  1 | ftp   | www.myhost.com  | secret.tgz
  2 | http  | www.myhost.com  | robots.txt
  3 | http  | www.myhost.com  | index.php
  4 | https | www.myhost.com  | index.php
  5 | http  | www.myhost.com  | subdir/index.php
  6 | https | www.myhost.com  | subdir/index.php
  7 | http  | www.hishost.com | index.php
  8 | https | www.hishost.com | index.php
  9 | http  | www.herhost.com | index.php
 10 | https | www.herhost.com | index.php
(10 rows)

 id |                full_url                 | proto |    hostname     |     pathname     
----+-----------------------------------------+-------+-----------------+------------------
  1 | ftp://www.myhost.com/secret.tgz         | ftp   | www.myhost.com  | secret.tgz
  2 | http://www.myhost.com/robots.txt        | http  | www.myhost.com  | robots.txt
  3 | http://www.myhost.com/index.php         | http  | www.myhost.com  | index.php
  4 | https://www.myhost.com/index.php        | https | www.myhost.com  | index.php
  5 | http://www.myhost.com/subdir/index.php  | http  | www.myhost.com  | subdir/index.php
  6 | https://www.myhost.com/subdir/index.php | https | www.myhost.com  | subdir/index.php
  7 | http://www.hishost.com/index.php        | http  | www.hishost.com | index.php
  8 | https://www.hishost.com/index.php       | https | www.hishost.com | index.php
  9 | http://www.herhost.com/index.php        | http  | www.herhost.com | index.php
 10 | https://www.herhost.com/index.php       | https | www.herhost.com | index.php
(10 rows)