* Rows = 11 / 22 -- don't take the numbers too seriously; they are crude approximations based on estimated cardinality.
* The 11 comes from the LIMIT -- therefore useless in judging the efficiency. (The 22 may be 2*11; I don't know.) * Run the EXPLAINs without LIMIT -- that will avoid the bogus 11/22. * If the CREATE INDEX took only 0.67 sec, I surmise that you have very few rows in the table?? So this discussion is not necessarily valid in general cases. * What percentage of time values meet the WHERE? This has a big impact on the choice of explain plan and performance. * Set long_query_time = 0; to get it in the slowlog even if it is fast. Then look at the various extra values (such as filesort, on disk, temp table used, etc). * Do this (with each index): SHOW SESSION STATUS LIKE 'Handler_read%'; SELECT ... FORCE INDEX(...) ...; SHOW SESSION STATUS LIKE 'Handler_read%'; Then take the diffs of the handler counts. This will give you a pretty detailed idea of what is going on; better than the SlowLog. * INT(3) is not a 3-digit integer, it is a full 32-bit integer (4 bytes). Perhaps you should have SMALLINT UNSIGNED (2 bytes). * BIGINT takes 8 bytes -- usually over-sized. > -----Original Message----- > From: spameden [mailto:spame...@gmail.com] > Sent: Monday, October 15, 2012 1:42 PM > To: mysql@lists.mysql.com > Subject: mysql logs query with indexes used to the slow-log and not > logging if there is index in reverse order > > Hi, list. > > Sorry for the long subject, but I'm really interested in solving this > and need a help: > > I've got a table: > > mysql> show create table send_sms_test; > +---------------+------------------------------------------------------ > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > -------------------------------+ > | Table | Create > Table > | > +---------------+------------------------------------------------------ > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > ----------------------------------------------------------------------- > -------------------------------+ > | send_sms_test | CREATE TABLE `send_sms_test` ( > `sql_id` bigint(20) NOT NULL AUTO_INCREMENT, > `momt` enum('MO','MT') DEFAULT NULL, > `sender` varchar(20) DEFAULT NULL, > `receiver` varchar(20) DEFAULT NULL, > `udhdata` blob, > `msgdata` text, > `time` bigint(20) NOT NULL, > `smsc_id` varchar(255) DEFAULT 'main', > `service` varchar(255) DEFAULT NULL, > `account` varchar(255) DEFAULT NULL, > `id` bigint(20) DEFAULT NULL, > `sms_type` tinyint(1) DEFAULT '2', > `mclass` bigint(20) DEFAULT NULL, > `mwi` bigint(20) DEFAULT NULL, > `coding` bigint(20) DEFAULT NULL, > `compress` bigint(20) DEFAULT NULL, > `validity` bigint(20) DEFAULT NULL, > `deferred` bigint(20) DEFAULT NULL, > `dlr_mask` bigint(20) DEFAULT NULL, > `dlr_url` varchar(255) DEFAULT NULL, > `pid` bigint(20) DEFAULT NULL, > `alt_dcs` bigint(20) DEFAULT NULL, > `rpi` bigint(20) DEFAULT NULL, > `charset` varchar(255) DEFAULT NULL, > `boxc_id` varchar(255) DEFAULT NULL, > `binfo` varchar(255) DEFAULT NULL, > `meta_data` text, > `task_id` bigint(20) DEFAULT NULL, > `msgid` bigint(20) DEFAULT NULL, > `priority` int(3) unsigned NOT NULL DEFAULT '500', > PRIMARY KEY (`sql_id`), > KEY `task_id` (`task_id`), > KEY `receiver` (`receiver`), > KEY `msgid` (`msgid`), > KEY `priority_time` (`priority`,`time`) > ) ENGINE=InnoDB AUTO_INCREMENT=7806318 DEFAULT CHARSET=utf8 > > Slow-queries turned on with an option: > | log_queries_not_using_indexes | ON | > > mysqld --version > mysqld Ver 5.1.65-rel14.0 for debian-linux-gnu on x86_64 ((Percona > Server (GPL), 14.0, Revision 475)) > > If I check with EXPLAIN MySQL says it would use the index: > mysql> *desc select * from send_sms_test where > mysql> time<=UNIX_TIMESTAMP(NOW()) > order by priority limit 0,11;* > +----+-------------+---------------+-------+---------------+----------- > ----+---------+------+------+-------------+ > | id | select_type | table | type | possible_keys | key > | key_len | ref | rows | Extra | > +----+-------------+---------------+-------+---------------+----------- > ----+---------+------+------+-------------+ > | 1 | SIMPLE | send_sms_test | index | NULL | > priority_time > | 12 | NULL | * 11* | Using where | > +----+-------------+---------------+-------+---------------+----------- > ----+---------+------+------+-------------+ > 1 row in set (0.00 sec) > > But If I issue the query I see in the mysql-slow.log: > select * from send_sms_test where time<=UNIX_TIMESTAMP(NOW()) order by > priority limit 0,11; > > If I do create INDEX time,priority (in reverse order instead of > priority,time) I get still the same usage of priority_time key with the > same length, but rows now are doubled): > mysql> *create index time_priority ON send_sms_test (time,priority);* > Query OK, 0 rows affected (0.67 sec) > Records: 0 Duplicates: 0 Warnings: 0 > > mysql> *desc select * from send_sms_test where > mysql> time<=UNIX_TIMESTAMP(NOW()) > order by priority limit 0,11;* > +----+-------------+---------------+-------+---------------+----------- > ----+---------+------+------+-------------+ > | id | select_type | table | type | possible_keys | key > | key_len | ref | rows | Extra | > +----+-------------+---------------+-------+---------------+----------- > ----+---------+------+------+-------------+ > | 1 | SIMPLE | send_sms_test | index | time_priority | > priority_time > | 12 | NULL | *22* | Using where | > +----+-------------+---------------+-------+---------------+----------- > ----+---------+------+------+-------------+ > > And if both indexes created I do not have anymore this query in the > slow-log. > > Of course If I disable log_queries_not_using_indexes I get none of the > queries. > > So is it a bug inside Percona's implementation or it's generally MySQL > behavior? > > Thanks -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/mysql
