From: Dathan Pattishall
Date: January 18 2005 11:34pm
Subject: RE: Doubt about Performance
List-Archive: http://lists.mysql.com/mysql/178687
Message-Id: <62D6B7C12242244DA66D9A4428688D922E0863@fiexchange.friendster.local>
MIME-Version: 1.0
Content-Type: text/plain;
	charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable

=20




> -----Original Message-----
> From: Ronan Lucio [mailto:ronanl@stripped]=20
> Sent: Tuesday, January 18, 2005 10:13 AM
> To: mysql@stripped
> Subject: Doubt about Performance
>=20
> Hello,
>=20
> Trying to keep the database and the application fast, I=B4d=20
> like to clearify my mind about it.
>=20
> 1) Is a SELECT DISTINCT over 5,000 records a weight
>     query? (Supposing it has about 20 different option the the
>     DISTINCT key).

	This is not bad, it's a mysql function that uses a KEY if a key exist.

>=20
> 2) Is SELECT ORDER BY RAND() over 1,500 records
>     a weight query?
>=20
> I need to put these two queries in the first page of our site.
> So, I=B4ve been worried if it can slow down our site in the pics.

	DO SELECT ORDER BY RAND() LIMIT  <<< 1500=20

Such that <<< means much less then 1500 on the order of 10.

This is a rather expensive operation and should be used with care.

I've gotten around this by generating a random number in my app and =
trying to match it to a known id by making multiple selects. This was =
less intensive then ORDER BY RAND.

--
DVP
>=20
> Thanks,
> Ronan
>=20
>=20
>=20
> --
> MySQL General Mailing List
> For list archives: http://lists.mysql.com/mysql
> To unsubscribe:   =20
> http://lists.mysql.com/mysql?unsub=3Ddathan@stripped
>=20
>=20