Re: Performance Concern

John Pagakis kirjutas L, 25.10.2003 kell 12:56:

> I wrote a JAVA simulation of the above that did 1000 updates in 37 seconds.
> That left me scratching my head because in psql when I did the
> semi-equivalent:
>
> UPDATE baz SET customer_id = '1234' WHERE baz_key IN( SELECT baz_key FROM
> baz WHERE customer_id IS NULL LIMIT 1000 );

try it this way, maybe it will start using an index :

UPDATE baz
SET customer_id = '1234'
WHERE baz_key IN (
SELECT baz_key
FROM baz innerbaz
WHERE customer_id IS NULL
and innerbaz.baz_key = baz.baz_key
LIMIT 1000 );

you may also try to add a conditional index to baz:

CREATE INDEX baz_key_with_null_custid_nxd
ON baz
WHERE customer_id IS NULL;

to make the index access more efficient.

----------------
Hannu