Mysql query log

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