MySQL中查询日志与慢查询日志的基本学习教程
一、查询日志
查询日志记录MySQL中所有的query，通过\"--log[=file_name]\"来打开该功能。由于记录了所有的query，包括所有的select，体积比较大，开启后对性能也有比较大的影响，所以请大家慎用该功能。一般只用于跟踪某些特殊的sql性能问题才会短暂打开该功能。默认的查询日志文件名为：hostname.log.
----默认情况下查看是否启用查询日志：
[root@node4 mysql5.5]# service mysql start
Starting MySQL.... [ OK ]
[root@node4 mysql5.5]# 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 \'%log\';
+--------------------------------+-------+ | Variable_name | Value | +--------------------------------+-------+ | back_log | 50 | | general_log | OFF | | innodb_locks_unsafe_for_binlog | OFF | | log | OFF | | relay_log | | | slow_query_log | OFF | | sync_binlog | 0 | | sync_relay_log | 0 | +--------------------------------+-------+ 8 rows in set (0.00 sec)
----备注：log和general_log这两个参数是兼容的。而默认的情况下查询日志是不开启的
----使用下面的命令是开启查询日志
mysql> set global log=1;
Query OK, 0 rows affected, 1 warning (0.03 sec)
mysql> show variables like \'%log\';
+--------------------------------+-------+ | Variable_name | Value | +--------------------------------+-------+ | back_log | 50 | | general_log | ON | | innodb_locks_unsafe_for_binlog | OFF | | log | ON | | relay_log | | | slow_query_log | OFF | | sync_binlog | 0 | | sync_relay_log | 0 | +--------------------------------+-------+ 8 rows in set (0.00 sec) ----其中log参数是过时的，在启动选项中使用log参数的话，会在err日志中显示出来。 ----修改my.cnf文件，添加log的参数设置
[root@node4 mysql5.5]# vi my.cnf [root@node4 mysql5.5]# cat ./my.cnf |grep \'^log=\' log=/tmp/mysqlgen.log ----清空err日志 [root@node4 mysql5.5]# cat /dev/null > /tmp/mysql3306.err [root@node4 mysql5.5]# ll /tmp/mysql3306.err -rw-rw---- 1 mysql root 0 Jul 31 07:50 /tmp/mysql3306.err [root@node4 mysql5.5]# service mysql start
Starting MySQL... [ OK ] ----启动数据库后查看err日志的内容
[root@node4 mysql5.5]# cat /tmp/mysql3306.err
130731 07:51:32 mysqld_safe Starting mysqld daemon with databases from /opt/mysql5.5/data 130731 7:51:32 [Warning] The syntax \'--log\' is deprecated and will be removed in a future release. Please use \'--general-log\'/\'--general-log-file\' instead. 130731 7:51:33 InnoDB: The InnoDB memory heap is disabled 130731 7:51:33 InnoDB: Mutexes and rw_locks use InnoDB\'s own implementation 130731 7:51:33 InnoDB: Compressed tables use zlib 1.2.3 130731 7:51:33 InnoDB: Initializing buffer pool, size = 128.0M 130731 7:51:33 InnoDB: Completed initialization of buffer pool 130731 7:51:33 InnoDB: highest supported file format is Barracuda. 130731 7:51:33 InnoDB: Waiting for the background threads to start 130731 7:51:34 InnoDB: 1.1.8 started; log sequence number 1625855 130731 7:51:34 [Note] Event Scheduler: Loaded 0 events 130731 7:51:34 [Note] /opt/mysql5.5/bin/mysqld: ready for connections. Version: \'5.5.22-log\' socket: \'/tmp/mysql.sock\' port: 3306 Source distribution ----使用最新的参数 ----general_log和general_log_file。
[root@node4 mysql5.5]# service mysql stop
Shutting down MySQL. [ OK ]
[root@node4 mysql5.5]# vi my.cnf [root@node4 mysql5.5]# cat ./my.cnf |grep \'^general\'
general_log = 1 general_log_file = /tmp/mysqlgen.log
[root@node4 mysql5.5]# service mysql start
Starting MySQL... [ OK ]
[root@node4 mysql5.5]# 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 \'%log\';
+--------------------------------+-------+ | Variable_name | Value | +--------------------------------+-------+ | back_log | 50 | | general_log | ON | | innodb_locks_unsafe_for_binlog | OFF | | log | ON | | relay_log | | | slow_query_log | OFF | | sync_binlog | 0 | | sync_relay_log | 0 | +--------------------------------+-------+ 8 rows in set (0.04 sec)
mysql> show variables like \'%file\';
+---------------------+-----------------------------------+ | Variable_name | Value | +---------------------+-----------------------------------+ | ft_stopword_file | (built-in) | | general_log_file | /tmp/mysqlgen.log | | init_file | | | local_infile | ON | | pid_file | /tmp/mysql3306.pid | | relay_log_info_file | relay-log.info | | slow_query_log_file | /opt/mysql5.5/data/node4-slow.log | +---------------------+-----------------------------------+ 7 rows in set (0.00 sec) ----在上面的操作中可以看到已经启用查询日志，并且文件目录是/tmp/mysqlgen.log。 ----查询日志记录了哪些东西？
进行下面的查询
mysql> show databases;
+--------------------+ | Database | +--------------------+ | information_schema | | mysql | | performance_schema | | test | | test2 | +--------------------+ 5 rows in set (0.08 sec)
mysql> use test;
Database changed
mysql> show tables;
Empty set (0.00 sec)
mysql> use test2;
Database changed
mysql> show tables;
+-----------------+ | Tables_in_test2 | +-----------------+ | course | | jack | | sc | | student | | t | | teacher | +-----------------+ 6 rows in set (0.07 sec)
mysql> drop table t;
Query OK, 0 rows affected (0.13 sec)
mysql> select * from sc;
Empty set (0.04 sec) ----可以看到上面的操作都记录在了mysqlgen.log里面。
[root@node4 ~]# tail -f /tmp/mysqlgen.log
/opt/mysql5.5/bin/mysqld, Version: 5.5.22-log (Source distribution). started with:
Tcp port: 3306 Unix socket: /tmp/mysql.sock
Time Id Command Argument
130731 7:55:41 1 Query show databases
130731 7:55:56 1 Query SELECT DATABASE()
1 Init DB test
130731 7:55:59 1 Query show tables
130731 7:56:19 1 Query SELECT DATABASE()
1 Init DB test2
130731 7:56:23 1 Query show tables
130731 7:56:27 1 Query drop table t
130731 7:56:39 1 Query select * from sc
二、慢查询日志
顾名思义，慢查询日志中记录的是执行时间较长的query，也就是我们常说的slow query，通过设--log-slow-queries[=file_name]来打开该功能并设置记录位置和文件名，默认文件名为hostname-slow.log，默认目录也是数据目录。
慢查询日志采用的是简单的文本格式，可以通过各种文本编辑器查看其中的内容。其中记录了语句执行的时刻，执行所消耗的时间，执行用户，连接主机等相关信息。MySQL还提供了专门用来分析满查询日志的工具程序mysqlslowdump，用来帮助数据库管理人员解决可能存在的性能问题。
----使用log_slow_queries参数打开慢查询，由于该参数已经过时，因此在err日志中将出现提示信息
----修改my.cnf文件，添加log_slow_queries参数 [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日志内容： [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
02:26:28 mysqld_safe Starting mysqld daemon with databases from /opt/mysql5.5/data 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. 2:26:28 [Warning] You need to use --log-bin to make --binlog-format work. 2:26:28 InnoDB: The InnoDB memory heap is disabled 2:26:28 InnoDB: Mutexes and rw_locks use InnoDB\'s own implementation 2:26:28 InnoDB: Compressed tables use zlib 1.2.3 2:26:28 InnoDB: Initializing buffer pool, size = 128.0M 2:26:28 InnoDB: Completed initialization of buffer pool 2:26:28 InnoDB: highest supported file format is Barracuda. 2:26:28 InnoDB: Waiting for the background threads to start 2:26:30 InnoDB: 1.1.8 started; log sequence number 3069452 2:26:30 [Note] Event Scheduler: Loaded 0 events 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 | +---------------------+---------------------+ rows in set (0.00 sec)
----关于slow_launch_time参数，首先修改一下参数值 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 | +-----------------+----------+ row in set (0.00 sec)
----进行一下相关操作，查看/tmp/mysqlslow.log1的内容
mysql> select database();
+------------+ | database() | +------------+ | NULL | +------------+ 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 ----在这里已经超过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参数实验
mysql> show variables like \'%indexes%\';
+-------------------------------+-------+ | Variable_name | Value | +-------------------------------+-------+ | log_queries_not_using_indexes | OFF | +-------------------------------+-------+ 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 | +-------------------------------+-------+ 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 | | | | +-----------------+---------------------+------+-----+---------+-------+ 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\';
PS：slow query log相关变量
命令行参数：
--log-slow-queries
指定日志文件存放位置，可以为空，系统会给一个缺省的文件host_name-slow.log
系统变量
log_slow_queries
指定日志文件存放位置，可以为空，系统会给一个缺省的文件host_name-slow.log
slow_query_log
slow quere log的开关，当值为1的时候说明开启慢查询。
slow_query_log_file
指定日志文件存放位置，可以为空，系统会给一个缺省的文件host_name-slow.log
long_query_time
记录超过的时间，默认为10s
log_queries_not_using_indexes
log下来没有使用索引的query，可以根据情况决定是否开启
三、Mysqldumpslow
如果日志内容很多，用眼睛一条一条看会累死，mysql自带了分析的工具，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
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