一、概念部分：
顧名思義，慢查詢日志中記錄的是執行時間較長的query，也就是我們常說的slow query，通過設--log-slow-queries[=file_name]來打開該功能並設置記錄位置和文件名，默認文件名為hostname-slow.log，默認目錄也是數據目錄。
慢查詢日志采用的是簡單的文本格式，可以通過各種文本編輯器查看其中的內容。其中記錄了語句執行的時刻，執行所消耗的時間，執行用戶，連接主機等相關信息。MySQL還提供了專門用來分析滿查詢日志的工具程序mysqlslowdump，用來幫助數據庫管理人員解決可能存在的性能問題。
二、slow query log相關變量
2.1、命令行參數：
--log-slow-queries
指定日志文件存放位置，可以為空，系統會給一個缺省的文件host_name-slow.log
2.2、系統變量
log_slow_queries
指定日志文件存放位置，可以為空，系統會給一個缺省的文件host_name-slow.log
slow_query_log
slow quere log的開關，當值為1的時候說明開啟慢查詢。
slow_query_log_file
指定日志文件存放位置，可以為空，系統會給一個缺省的文件host_name-slow.log
long_query_time
記錄超過的時間，默認為10s
log_queries_not_using_indexes
log下來沒有使用索引的query，可以根據情況決定是否開啟
三、實驗部分：
----使用log_slow_queries參數打開慢查詢，由於該參數已經過時，因此在err日志中將出現提示信息 ----修改my.cnf文件，添加log_slow_queries參數 [root@node4 ~]# vi /opt/mysql5.5/my.cnf [root@node4 ~]# cat /opt/mysql5.5/my.cnf |grep '^log_slow' log_slow_queries = /tmp/mysqlslow.log ----清空err日志內容： [root@node4 ~]# cat /dev/null > /tmp/mysql3306.err [root@node4 ~]# service mysql start Starting MySQL.... [ OK ] ----查看err日志的信息 [root@node4 data]# tail -f /tmp/mysql3306.err 130801 02:26:28 mysqld_safe Starting mysqld daemon with databases from /opt/mysql5.5/data 130801 2:26:28 [Warning] The syntax '--log-slow-queries' is deprecated and will be removed in a future release. Please use '--slow-query-log'/'--slow-query-log-file' instead. 130801 2:26:28 [Warning] You need to use --log-bin to make --binlog-format work. 130801 2:26:28 InnoDB: The InnoDB memory heap is disabled 130801 2:26:28 InnoDB: Mutexes and rw_locks use InnoDB's own implementation 130801 2:26:28 InnoDB: Compressed tables use zlib 1.2.3 130801 2:26:28 InnoDB: Initializing buffer pool, size = 128.0M 130801 2:26:28 InnoDB: Completed initialization of buffer pool 130801 2:26:28 InnoDB: highest supported file format is Barracuda. 130801 2:26:28 InnoDB: Waiting for the background threads to start 130801 2:26:30 InnoDB: 1.1.8 started; log sequence number 3069452 130801 2:26:30 [Note] Event Scheduler: Loaded 0 events 130801 2:26:30 [Note] /opt/mysql5.5/bin/mysqld: ready for connections. Version: '5.5.22-log' socket: '/tmp/mysql.sock' port: 3306 Source distribution ----使用slow_query_log和slow_query_log_file [root@node4 ~]# vi /opt/mysql5.5/my.cnf [root@node4 ~]# cat /opt/mysql5.5/my.cnf |grep '^slow_query' slow_query_log = 1 slow_query_log_file = /tmp/mysqlslow.log1 [root@node4 ~]# service mysql start Starting MySQL... [ OK ] [root@node4 ~]# mysql Welcome to the MySQL monitor. Commands end with ; or \g. Your MySQL connection id is 1 Server version: 5.5.22-log Source distribution Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved. Oracle is a registered trademark of Oracle Corporation and/or its affiliates. Other names may be trademarks of their respective owners. Type 'help;' or '\h' for help. Type '\c' to clear the current input statement. mysql> show variables like '%slow%'; +---------------------+---------------------+ | Variable_name | Value | +---------------------+---------------------+ | log_slow_queries | ON | | slow_launch_time | 10 | | slow_query_log | ON | | slow_query_log_file | /tmp/mysqlslow.log1 | +---------------------+---------------------+ 4 rows in set (0.00 sec) ----關於slow_launch_time參數，首先修改一下參數值 mysql> set global long_query_time=1; Query OK, 0 rows affected (0.00 sec) mysql> show variables like '%long_query%'; +-----------------+----------+ | Variable_name | Value | +-----------------+----------+ | long_query_time | 1.000000 | +-----------------+----------+ 1 row in set (0.00 sec) ----進行一下相關操作，查看/tmp/mysqlslow.log1的內容 mysql> select database(); +------------+ | database() | +------------+ | NULL | +------------+ 1 row in set (0.00 sec) mysql> use test; Database changed mysql> show tables; Empty set (0.00 sec) mysql> create table t as select * from information_schema.tables; Query OK, 85 rows affected (0.38 sec) Records: 85 Duplicates: 0 Warnings: 0 mysql> insert into t select * from t; Query OK, 85 rows affected (0.05 sec) Records: 85 Duplicates: 0 Warnings: 0 mysql> insert into t select * from t; Query OK, 170 rows affected (0.03 sec) Records: 170 Duplicates: 0 Warnings: 0 mysql> insert into t select * from t; Query OK, 340 rows affected (0.05 sec) Records: 340 Duplicates: 0 Warnings: 0 mysql> insert into t select * from t; Query OK, 680 rows affected (0.08 sec) Records: 680 Duplicates: 0 Warnings: 0 mysql> insert into t select * from t; Query OK, 1360 rows affected (0.29 sec) Records: 1360 Duplicates: 0 Warnings: 0 mysql> insert into t select * from t; Query OK, 2720 rows affected (1.49 sec) Records: 2720 Duplicates: 0 Warnings: 0 ----在這里已經超過1s了，查看/tmp/mysqlslow.log1 [root@node4 data]# tail -f /tmp/mysqlslow.log1 # Time: 130801 2:36:25 # User@Host: root[root] @ localhost [] # Query_time: 2.274219 Lock_time: 0.000322 Rows_sent: 0 Rows_examined: 5440 use test; SET timestamp=1375295785; insert into t select * from t; ----log_queries_not_using_indexes參數實驗 mysql> show variables like '%indexes%'; +-------------------------------+-------+ | Variable_name | Value | +-------------------------------+-------+ | log_queries_not_using_indexes | OFF | +-------------------------------+-------+ 1 row in set (0.00 sec) mysql> set log_queries_not_using_indexes = 1; ERROR 1229 (HY000): Variable 'log_queries_not_using_indexes' is a GLOBAL variable and should be set with SET GLOBAL mysql> set global log_queries_not_using_indexes = 1; Query OK, 0 rows affected (0.01 sec) mysql> show variables like '%indexes%'; +-------------------------------+-------+ | Variable_name | Value | +-------------------------------+-------+ | log_queries_not_using_indexes | ON | +-------------------------------+-------+ 1 row in set (0.00 sec) mysql> desc t; +-----------------+---------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-----------------+---------------------+------+-----+---------+-------+ | TABLE_CATALOG | varchar(512) | NO | | | | | TABLE_SCHEMA | varchar(64) | NO | | | | | TABLE_NAME | varchar(64) | NO | | | | | TABLE_TYPE | varchar(64) | NO | | | | | ENGINE | varchar(64) | YES | | NULL | | | VERSION | bigint(21) unsigned | YES | | NULL | | | ROW_FORMAT | varchar(10) | YES | | NULL | | | TABLE_ROWS | bigint(21) unsigned | YES | | NULL | | | AVG_ROW_LENGTH | bigint(21) unsigned | YES | | NULL | | | DATA_LENGTH | bigint(21) unsigned | YES | | NULL | | | MAX_DATA_LENGTH | bigint(21) unsigned | YES | | NULL | | | INDEX_LENGTH | bigint(21) unsigned | YES | | NULL | | | DATA_FREE | bigint(21) unsigned | YES | | NULL | | | AUTO_INCREMENT | bigint(21) unsigned | YES | | NULL | | | CREATE_TIME | datetime | YES | | NULL | | | UPDATE_TIME | datetime | YES | | NULL | | | CHECK_TIME | datetime | YES | | NULL | | | TABLE_COLLATION | varchar(32) | YES | | NULL | | | CHECKSUM | bigint(21) unsigned | YES | | NULL | | | CREATE_OPTIONS | varchar(255) | YES | | NULL | | | TABLE_COMMENT | varchar(2048) | NO | | | | +-----------------+---------------------+------+-----+---------+-------+ 21 rows in set (0.05 sec) ----下面的命令是查看索引的 mysql> show index from t; Empty set (0.01 sec) mysql> select * from t where engine='xxx'; Empty set (0.18 sec) # Time: 130801 2:43:43 # User@Host: root[root] @ localhost [] # Query_time: 0.185773 Lock_time: 0.148868 Rows_sent: 0 Rows_examined: 5440 SET timestamp=1375296223; select * from t where engine='xxx';
四、Mysqldumpslow
如果日志內容很多，用眼睛一條一條看會累死，mysql自帶了分析的工具，使用方法如下：
[root@node4 data]# mysqldumpslow --help Usage: mysqldumpslow [ OPTS... ] [ LOGS... ] Parse and summarize the MySQL slow query log. Options are --verbose verbose --debug debug --help write this text to standard output -v verbose -d debug -s ORDER what to sort by (al, at, ar, c, l, r, t), 'at' is default al: average lock time ar: average rows sent at: average query time c: count l: lock time r: rows sent t: query time -r reverse the sort order (largest last instead of first) -t NUM just show the top n queries -a don't abstract all numbers to N and strings to 'S' -n NUM abstract numbers with at least n digits within names -g PATTERN grep: only consider stmts that include this string -h HOSTNAME hostname of db server for *-slow.log filename (can be wildcard), default is '*', i.e. match all -i NAME name of server instance (if using mysql.server startup script) -l don't subtract lock time from total time