Thanks a lot for all your comments! I did disable Query cache before testing with
set query_cache_type=OFF for the current session. I will report this to the MySQL bugs site later. 2012/10/16 Rick James <rja...@yahoo-inc.com> > **Ø **My initial question was why MySQL logs it in the slow log if the > query uses an INDEX? > > **** > > That _may_ be worth a bug report.**** > > ** ** > > A _possible_ answer... EXPLAIN presents what the optimizer is in the mood > for at that moment. It does not necessarily reflect what it was in the > mood for when it ran the query.**** > > ** ** > > When timing things, run them twice (and be sure not to hit the Query > cache). The first time freshens the cache (buffer_pool, etc); the second > time gives you a 'reproducible' time. I believe (without proof) that the > cache contents can affect the optimizer's choice.**** > > ** ** > > *From:* spameden [mailto:spame...@gmail.com] > *Sent:* Monday, October 15, 2012 3:29 PM > > *To:* Rick James > *Cc:* mysql@lists.mysql.com > *Subject:* Re: mysql logs query with indexes used to the slow-log and not > logging if there is index in reverse order**** > > ** ** > > Sorry, forgot to say: > > mysql> show variables like 'long_query_time%'; > +-----------------+-----------+ > | Variable_name | Value | > +-----------------+-----------+ > | long_query_time | 10.000000 | > +-----------------+-----------+ > 1 row in set (0.00 sec) > > It's getting in the log only due: > > mysql> show variables like '%indexes%'; > +-------------------------------+-------+ > | Variable_name | Value | > +-------------------------------+-------+ > | log_queries_not_using_indexes | ON | > +-------------------------------+-------+ > 1 row in set (0.00 sec) > > If I turn it off - it's all fine > > My initial question was why MySQL logs it in the slow log if the query > uses an INDEX? > > And why it's not logging if I create an INDEX (time, priority) (but in the > query there is FORCE INDEX (priority,time) specified, so MySQL shouldn't > use newly created INDEX (time, priority) at all).**** > > 2012/10/16 spameden <spame...@gmail.com>**** > > Sorry, my previous e-mail was a test on MySQL-5.5.28 on an empty table. > > Here is the MySQL-5.1 Percona testing table: > > mysql> select count(*) from send_sms_test; > +----------+ > | count(*) | > +----------+ > | 143879 | > +----------+ > 1 row in set (0.03 sec) > > Without LIMIT: > mysql> desc select * from send_sms_test FORCE INDEX (time_priority) where > time<=UNIX_TIMESTAMP(NOW()) order by priority; > > +----+-------------+---------------+-------+---------------+---------------+---------+------+-------+-----------------------------+ > **** > > > | id | select_type | table | type | possible_keys | key > | key_len | ref | rows | Extra |**** > > > +----+-------------+---------------+-------+---------------+---------------+---------+------+-------+-----------------------------+ > | 1 | SIMPLE | send_sms_test | range | time_priority | time_priority > | 8 | NULL | 73920 | Using where; Using filesort | > > +----+-------------+---------------+-------+---------------+---------------+---------+------+-------+-----------------------------+ > **** > > 1 row in set (0.00 sec)**** > > mysql> desc select * from send_sms_test FORCE INDEX (priority_time) where > time<=UNIX_TIMESTAMP(NOW()) order by priority; > > +----+-------------+---------------+-------+---------------+---------------+---------+------+--------+-------------+ > **** > > > | id | select_type | table | type | possible_keys | key > | key_len | ref | rows | Extra |**** > > > +----+-------------+---------------+-------+---------------+---------------+---------+------+--------+-------------+ > | 1 | SIMPLE | send_sms_test | index | NULL | priority_time > | 12 | NULL | 147840 | Using where | > > +----+-------------+---------------+-------+---------------+---------------+---------+------+--------+-------------+ > **** > > > 1 row in set (0.00 sec)**** > > But I actually need to use LIMIT, because client uses this to limit the > number of records returned to process. > > mysql> select * from send_sms_test FORCE INDEX (priority_time) where > time<=UNIX_TIMESTAMP(NOW()) order by priority LIMIT 0,100; > 100 rows in set (0.00 sec) > > mysql> show profile; > +--------------------+----------+ > | Status | Duration | > +--------------------+----------+ > | starting | 0.000053 | > | Opening tables | 0.000009 | > | System lock | 0.000005 | > | Table lock | 0.000004 | > | init | 0.000037 | > | optimizing | 0.000005 | > | statistics | 0.000007 | > | preparing | 0.000005 | > | executing | 0.000001 | > | Sorting result | 0.000003 | > | Sending data | 0.000856 | > | end | 0.000003 | > | query end | 0.000001 | > | freeing items | 0.000015 | > | logging slow query | 0.000001 | > | logging slow query | 0.000047 | > | cleaning up | 0.000002 | > +--------------------+----------+ > 17 rows in set (0.00 sec) > > mysql> select * from send_sms_test FORCE INDEX (time_priority) where > time<=UNIX_TIMESTAMP(NOW()) order by priority LIMIT 0,100; > 100 rows in set (0.08 sec) > mysql> show profile; > +--------------------+----------+ > | Status | Duration | > +--------------------+----------+ > | starting | 0.000048 | > | Opening tables | 0.000009 | > | System lock | 0.000002 | > | Table lock | 0.000004 | > | init | 0.000047 | > | optimizing | 0.000006 | > | statistics | 0.000043 | > | preparing | 0.000018 | > | executing | 0.000001 | > | Sorting result | 0.076725 | > | Sending data | 0.001406 | > | end | 0.000003 | > | query end | 0.000001 | > | freeing items | 0.000012 | > | logging slow query | 0.000001 | > | cleaning up | 0.000002 | > +--------------------+----------+ > 16 rows in set (0.00 sec) > > As you can see latter query takes more time, because it's using filesort > as well. > > Now, handler: > mysql> SHOW SESSION STATUS LIKE 'Handler_read%';select * from > send_sms_test FORCE INDEX (priority_time) where time<=UNIX_TIMESTAMP(NOW()) > order by priority LIMIT 0,100;SHOW SESSION STATUS LIKE 'Handler_read%'; > +-----------------------+--------+ > | Variable_name | Value | > +-----------------------+--------+ > | Handler_read_first | 18 | > | Handler_read_key | 244 | > | Handler_read_next | 719969 | > | Handler_read_prev | 0 | > | Handler_read_rnd | 226 | > | Handler_read_rnd_next | 223 | > +-----------------------+--------+ > 6 rows in set (0.00 sec) > .... 100 rows in set (0.00 sec) > +-----------------------+--------+ > | Variable_name | Value | > +-----------------------+--------+ > | Handler_read_first | 19 | > | Handler_read_key | 245 | > | Handler_read_next | 720068 | > | Handler_read_prev | 0 | > | Handler_read_rnd | 226 | > | Handler_read_rnd_next | 223 | > +-----------------------+--------+ > 6 rows in set (0.00 sec) > > > mysql> SHOW SESSION STATUS LIKE 'Handler_read%'; > +-----------------------+--------+ > | Variable_name | Value | > +-----------------------+--------+ > | Handler_read_first | 17 | > | Handler_read_key | 143 | > | Handler_read_next | 576090 | > | Handler_read_prev | 0 | > | Handler_read_rnd | 126 | > | Handler_read_rnd_next | 223 | > +-----------------------+--------+ > 6 rows in set (0.00 sec) > > mysql> select * from send_sms_test FORCE INDEX (time_priority) where > time<=UNIX_TIMESTAMP(NOW()) order by priority LIMIT 0,100; > 100 rows in set (0.09 sec) > > mysql> SHOW SESSION STATUS LIKE 'Handler_read%'; > +-----------------------+--------+ > | Variable_name | Value | > +-----------------------+--------+ > | Handler_read_first | 18 | > | Handler_read_key | 244 | > | Handler_read_next | 719969 | > | Handler_read_prev | 0 | > | Handler_read_rnd | 226 | > | Handler_read_rnd_next | 223 | > +-----------------------+--------+ > 6 rows in set (0.00 sec) > > I don't understand much in Handler thing, could you please explain more, > based on the results I've posted ? In which case it works better and how it > uses the index? > > About BIGINT(20) and INT(3) I will look further into this later, I > understand it might be oversized, but my main question is about index why > it's using it so weird. > > Many thanks for your quick answer!**** > > ** ** > > 2012/10/16 Rick James <rja...@yahoo-inc.com>**** > > * 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**** > > ** ** > > ** ** >
