Finding optimal indexes for this MySQL query - mysql

Question

I'm struggling to understand if I've indexed this query properly, it's somewhat slow and I feel it could use optimization. MySQL 5.1.70
select snaps.id, snaps.userid, snaps.ins_time, usr.gender
from usersnaps as snaps
join user as usr on usr.id = snaps.userid
left join user_convert as conv on snaps.userid = conv.userid
where (conv.level is null or conv.level = 4) and snaps.active = 'N'
and (usr.status = "unfilled" or usr.status = "unapproved") and usr.active = 1
order by snaps.ins_time asc
usersnaps table (irrelevant deta removed, size about 250k records) :
CREATE TABLE IF NOT EXISTS `usersnaps` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`userid` int(11) unsigned NOT NULL DEFAULT '0',
`picture` varchar(250) NOT NULL,
`active` enum('N','Y') NOT NULL DEFAULT 'N',
`ins_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
PRIMARY KEY (`id`,`userid`),
KEY `userid` (`userid`,`active`),
KEY `ins_time` (`ins_time`),
KEY `active` (`active`)
) ENGINE=InnoDB;
user table (irrelevant deta removed, size about 300k records) :
CREATE TABLE IF NOT EXISTS `user` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`active` tinyint(1) NOT NULL DEFAULT '1',
`status` enum('15','active','approval','suspended','unapproved','unfilled','rejected','suspended_auto','incomplete') NOT NULL DEFAULT 'approval',
PRIMARY KEY (`id`),
KEY `status` (`status`,`active`)
) ENGINE=InnoDB;
user_convert table (size about : 60k records) :
CREATE TABLE IF NOT EXISTS `user_convert` (
`userid` int(10) unsigned NOT NULL,
`level` tinyint(4) NOT NULL,
UNIQUE KEY `userid` (`userid`),
KEY `level` (`level`)
) ENGINE=InnoDB;
Explain extended returns :
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE snaps ref userid,default_pic,active active 1 const 65248 100.00 Using where; Using filesort
1 SIMPLE usr eq_ref PRIMARY,active,status PRIMARY 4 snaps.userid 1 100.00 Using where
1 SIMPLE conv eq_ref userid userid 4s snaps.userid 1 100.00 Using where

Answer 1

Using filesort is probably your performance killer.
You need the records from usersnaps where active = 'N' and you need them sorted by ins_time.
ALTER TABLE usersnaps ADD KEY active_ins_time (active,ins_time);
Indexes are stored in sorted order, and read in sorted order... so if the optimizer chooses that index, it will go for the records with active = 'N' and -- hey, look at that -- they're already sorted by ins_time -- because of that index. So as it reads the rows referenced by the index, the result-set internally is already in the order you want it to ORDER BY, and the optimizer should realize this... no filesort required.

Answer 2

I would recommend changing the userid index (assuming you're not using it right now) to have active first and userid later.
That should make it more useful for this query.