In MySQL 5, SELECT COUNT(1) FROM table_name is very slow -

-

i have mysql 5.0 database few tables containing on 50m rows. how know this? running "select count(1) foo", of course. query on 1 table containing 58.8m rows took 10 minutes complete!

mysql> select count(1) large_table; +----------+ | count(1) | +----------+ | 58778494 |  +----------+ 1 row in set (10 min 23.88 sec)  mysql> explain select count(1) large_table; +----+-------------+-------------------+-------+---------------+----------------------------------------+---------+------+-----------+-------------+ | id | select_type | table             | type  | possible_keys | key                                    | key_len | ref  | rows      |       | +----+-------------+-------------------+-------+---------------+----------------------------------------+---------+------+-----------+-------------+ |  1 | simple      | large_table       | index | null          | fk_large_table_other_table_id          | 5       | null | 167567567 | using index |  +----+-------------+-------------------+-------+---------------+----------------------------------------+---------+------+-----------+-------------+ 1 row in set (0.00 sec)  mysql> desc large_table; +-------------------+---------------------+------+-----+---------+----------------+ | field             | type                | null | key | default |          | +-------------------+---------------------+------+-----+---------+----------------+ | id                | bigint(20) unsigned | no   | pri | null    | auto_increment |  | created_on        | datetime            | yes  |     | null    |                |  | updated_on        | datetime            | yes  |     | null    |                |  | other_table_id    | int(11)             | yes  | mul | null    |                |  | parent_id         | bigint(20) unsigned | yes  | mul | null    |                |  | name              | varchar(255)        | yes  |     | null    |                |  | property_type     | varchar(64)         | yes  |     | null    |                |  +-------------------+---------------------+------+-----+---------+----------------+ 7 rows in set (0.00 sec)

all of tables in question innodb.

any ideas why slow, , how can speed up?

if need have result instantly , don't care if it's 58.8m or 51.7m, can find out approximate number of rows calling

show table status 'large_table';

see column rows
more information result take @ manual @ http://dev.mysql.com/doc/refman/5.1/en/show-table-status.html


Comments

Post a Comment

Popular posts from this blog

Javascript line number mapping -

-
magically formatted comments change reported line number of javascript errors in browsers; this: //@line n "f" n line number , f file name. unfortunately, //@line appears ungoogleable. know there documentation on feature, , browsers support it? (i found references here , here .) from can find available in mozilla based browsers. it using js_setoptions command can turn these options on or off depending on values passed. https://developer.mozilla.org/en/js_setoptions
Read more

c# - Is it possible to remove an existing registration from Autofac container builder? -

-
something along lines: builder.registertype<mytype>().as<itype>(); builder.registertype<mytype2>().as<itype>(); builder.deregistertype<mytype>().as<itype>() var container = builder.build(); var types = container.resolve<ienumerable<itype>>(); assert.istrue(types.count == 1); assert.istrue(types[0].gettype == typeof(mytype2)); scenario: go through bunch of assemblies , go register types want make sure have 1 implementation of given type. need before create container. track on own nice if autofac me bit. this cannot done directly using containerbuilder , unless start on new one. mind you, having first built container should able construct new container filtering away unwanted types , reusing registrations first container. this: ... var container = builder.build(); builder = new containerbuilder(); var components = container.componentregistry.registrations .where(cr => cr.activator.limittype != typ...
Read more

php - Mysql PK and FK char(36) vs int(10) -

-
i have read mysql can handle indexes , searches better if tables keys integers rather char(36) uuid's. is worth converting int(10)? note: use 1 server , have have plans use multiple databases concurrently therefore removing 1 of big reasons using uuid. our tables innodb if makes difference. thanks in advance. usually rdbms can handle integer keys pk more efficient, other datatypes. reason how build index column, yes: long dont require string (or other typed) keys, should use integers. however: char(36) , int(10) far away being equal, because int(10) much smaller, char(36). dont know, if require many different keys, should keep in mind. update, complete last paragraph: int(10) 32-bit, char(36) 36 - ^byte^ (= 288-bit). not mean, int consumes less space, means, char(36) has 4 times more different keys.
Read more