MySQL select with where takes a long time - mysql

Question

I have a table with about 700.000 rows:
CREATE TABLE IF NOT EXISTS `ext_log_entries` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`action` varchar(8) NOT NULL,
`logged_at` datetime NOT NULL,
`object_id` varchar(32) DEFAULT NULL,
`object_class` varchar(255) NOT NULL,
`version` int(11) NOT NULL,
`data` longtext COMMENT '(DC2Type:array)',
`username` varchar(255) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `log_date_lookup_idx` (`logged_at`),
KEY `log_user_lookup_idx` (`username`),
KEY `log_class_lookup_idx` (`object_class`),
KEY `log_version_lookup_idx` (`object_id`,`object_class`,`version`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=1219777 ;
I try to run the following query:
SELECT n0_.id AS id0, n0_.action AS action1, n0_.logged_at AS logged_at2, n0_.object_id AS object_id3, n0_.object_class AS object_class4, n0_.version AS version5, n0_.data AS data6, n0_.username AS username7
FROM ext_log_entries n0_
WHERE n0_.object_id =275634
AND n0_.object_class = 'My\\MyBundle\\Entity\\Field'
AND n0_.version <=1
ORDER BY n0_.version ASC
Here is the MySQL plan:
id 1
select_type SIMPLE
table n0_
type ref
possible_keys log_class_lookup_idx,log_version_lookup_idx
key log_class_lookup_idx
key_len 767
ref const
rows 641159
Extra Using where; Using filesort
My query need about 37 seconds to be executed for only 1 row in the result...
I tried to run the same query by deleting my indexes and it goes a little bit faster : about 31 seconds...
I don't understand why my query is taking so much time and why my indexes don't help the performance? Do you know how I can do to have good performance on this query?
Thanks in advance for your help !
EDIT
Here are the cardinalties of the indexes
log_date_lookup_idx BTREE logged_at 1221578 A
log_user_lookup_idx BTREE username 40 A YES
log_class_lookup_idx BTREE object_class 1010 A
log_version_lookup_idx BTREE object_id 1221578 A YES
object_class 1221578 A
version 1221578 A

Answer 1

I found a solution, not THE solution, but at least it works for me.
I think it could help anyway all people who are using gedmo loggable and who are lucky (like me) to have objects with only integers IDs.
I changes my column object_id to integer instead of varchar(255). My query now take 0.008 second ! It works for me because i'm sure i'll always have only integers, for people who have varchar, I'm sorry i tried many things but nothing worked....
CREATE TABLE IF NOT EXISTS `ext_log_entries` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`action` varchar(8) NOT NULL,
`logged_at` datetime NOT NULL,
`object_id` int(11) DEFAULT NULL,
`object_class` varchar(255) NOT NULL,
`version` int(11) NOT NULL,
`data` longtext COMMENT '(DC2Type:array)',
`username` varchar(255) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `log_date_lookup_idx` (`logged_at`),
KEY `log_user_lookup_idx` (`username`),
KEY `log_class_lookup_idx` (`object_class`),
KEY `log_version_lookup_idx` (`object_id`,`object_class`,`version`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=1219777 ;