一、查询日志的概念：
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.
To enable the general query log as of MySQL 5.1.6,start mysqld with the --log option,and optionally use --log-ouput to specify the log output destination as described in Section 5.11.1,"Server Log Tables",Before 5.1.6,enable the general query log file with the --log[=file_name]or -l[file_name] option.If no file_name value is give,the default name is host_name,log in the data directory.
Server restarts and log flushing do not cause a new general query log file to be generated (although flushingcloses and reopens it).On Unix,you can rename the file and create a new one by using the following commands:
shell> my host_name.log host_name-old.log
shell> mysqladmin flush-logs
shell> cp host_name-old.log backup-directory
shell> rm host_name-old.log
二、实验部分：
----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