MySQL index question

Jeffrey_LSTaylor · July 20, 2010, 4:14pm

I am trying to speed up some DB operations and perhaps have gone
overboard
with indexes. Does MySQL usually use only one index per query and
simply
match keys on the results of the indexed first part? For example:

DELETE FROM tokens WHERE 6813946236211560448 <= fnv AND fnv <
6818449835838930944 AND updated_at<‘2010-06-20 14:08:55’ AND
occurrences=0;

If I understand correctly from the output of:

EXPLAIN SELECT * FROM tokens WHERE 6813946236211560448 <= fnv AND fnv <
6818449835838930944 AND updated_at<‘2010-06-20 14:08:55’ AND
occurrences=0;

only the index on fnv is used (there are indexes on updated_at and
occurrences).

Is this correct?

TIA,
Jeffrey

Jeffrey_LSTaylor · July 20, 2010, 4:38pm

On Jul 20, 3:12 pm, “Jeffrey L. Taylor” [email protected] wrote:

I am trying to speed up some DB operations and perhaps have gone overboard
with indexes. Does MySQL usually use only one index per query and simply
match keys on the results of the indexed first part? For example:

one one index will be used per table

Is this correct?
hard to say without said output

Fred

Jeffrey_LSTaylor · July 20, 2010, 4:57pm

Quoting Frederick C. [email protected]:

DELETE FROM tokens WHERE 6813946236211560448 <= fnv AND fnv < 6818449835838930944 AND updated_at<‘2010-06-20 14:08:55’ AND occurrences=0;
hard to say without said output

mysql> SHOW WARNINGS;

| Note | 1003 | select amethyst_production.tokens.fnv AS fnv,amethyst_production.tokens.user_id AS user_id,amethyst_production.tokens.occurrences AS occurrences,amethyst_production.tokens.clicks AS clicks,amethyst_production.tokens.hides AS hides,amethyst_production.tokens.ups AS ups,amethyst_production.tokens.downs AS downs,amethyst_production.tokens.expires AS expires,amethyst_production.tokens.token AS token,amethyst_production.tokens.created_at AS created_at,amethyst_production.tokens.updated_at AS updated_at from amethyst_production.tokens where ((amethyst_production.tokens.occurrences = 0) and (6813946236211560448 <= amethyst_production.tokens.fnv) and (amethyst_production.tokens.fnv < 6818449835838930944) and (amethyst_production.tokens.updated_at < _latin1’2010-06-20 14:08:55’))

Jeffrey

Jeffrey_LSTaylor · July 20, 2010, 5:08pm

On Jul 20, 3:55 pm, “Jeffrey L. Taylor” [email protected] wrote:

mysql> EXPLAIN EXTENDED SELECT * FROM tokens WHERE 6813946236211560448 <= fnv AND fnv < 6818449835838930944 AND updated_at<‘2010-06-20 14:08:55’ AND occurrences=0;
±—±------------±-------±------±------------------------------------- ------------------±--------------------------------±--------±-----±---- -±------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
±—±------------±-------±------±------------------------------------- ------------------±--------------------------------±--------±-----±---- -±------------+
| 1 | SIMPLE | tokens | range | index_tokens_on_fnv_and_user_id,updated_at,occurrences | index_tokens_on_fnv_and_user_id | 8 | NULL | 6153 | Using where |
±—±------------±-------±------±------------------------------------- ------------------±--------------------------------±--------±-----±---- -±------------+
1 row in set, 1 warning (0.00 sec)

Yup, that is just using the index on fnv.

Fred

Jeffrey_LSTaylor · July 20, 2010, 5:17pm

Quoting Frederick C. [email protected]:

Yup, that is just using the index on fnv.

Fred

Fred,
Thank you. Deleting the other indexes should speed up writes.

Jeffrey