MySQL中开启和使用通用查询日志的实例教程

开启通用查询日志
因为为了性能考虑，一般通用查询日志general log不会开启。slow log可以定位一些有性能问题的sql，而general log会记录所有的SQL。

mysql5.0版本，如果要开启slow log、general log，需要重启，从MySQL5.1.6版开始，general query log和slow query log开始支持写到文件或者数据库表两种方式，并且日志的开启，输出方式的修改，都可以在Global级别动态修改。

mysql>select version();

+————+
| version() |
+————+
| 5.1.37-log |
+————+
1 row in set (0.02 sec)

设置日志输出方式为文件（如果设置log_output=table的话，则日志结果会记录到名为gengera_log的表中，这表的默认引擎都是CSV）：

mysql>set global log_output=file;

Query OK, 0 rows affected (0.00 sec)

设置general log的日志文件路径：

mysql>set global general_log_file='/tmp/general.log';

Query OK, 0 rows affected (0.00 sec)

 开启general log：

mysql>set global general_log=on;

Query OK, 0 rows affected (0.02 sec)

过一段时间后，关闭general log：

mysql>set global general_log=off;

Query OK, 0 rows affected (0.02 sec)

通用查询日志的系统变量

log_output=[none|file|table|file,table] #通用查询日志输出格式

general_log=[on|off]      #是否启用通用查询日志

general_log_file[=filename]    #通用查询日志位置及名字

通用查询日志的备份

在Linux或Unix中，你可以通过下面的命令重新命名文件

并创建一个新文件：

shell> mv hostname.log hostname-old.log

shell> mysqladmin flush-logs

shell> cp hostname-old.log to-backup-directory

shell> rm hostname-old.log

在Windows中，服务器打开日志文件期间不能重新命名日志文件。必须先停止服务器然后重新命名日志文件。然后重启服务器来创建新日志文件。

演示通用查询日志的使用

a、启用通用查询日志

--演示环境
root@localhost[(none)]> show variables like '%version%';

+-------------------------+------------------------------+
| Variable_name  | Value  |
+-------------------------+------------------------------+
| innodb_version | 5.5.39  |
| protocol_version | 10   |
| slave_type_conversions |   |
| version  | 5.5.39-log  |
| version_comment | MySQL Community Server (GPL) |
| version_compile_machine | x86_64  |
| version_compile_os | Linux  |
+-------------------------+------------------------------+

--查看系统变量
root@localhost[(none)]> show variables like '%general%';

+------------------+----------------------------+
| Variable_name | Value  |
+------------------+----------------------------+
| general_log | OFF  |
| general_log_file | /var/lib/mysql/suse11b.log |
+------------------+----------------------------+

--查看当前的通用日志，显示无日志文件
root@localhost[(none)]> system ls /var/lib/mysql/suse11b.log 

ls: cannot access /var/lib/mysql/suse11b.log: No such file or directory

--设置变量general_log以开启通用查询日志
root@localhost[(none)]> set @@global.general_log=1;

Query OK, 0 rows affected (0.00 sec)

--再次查看通用日志文件已存在
root@localhost[(none)]> system ls /var/lib/mysql/suse11b.log 
/var/lib/mysql/suse11b.log
root@localhost[(none)]> select * from tempdb.tb1; --执行查询

+------+------+
| id | val |
+------+------+
| 1 | jack |
+------+------+

--查看通用日志文件内容
root@localhost[(none)]> system more /var/lib/mysql/suse11b.log
/usr/sbin/mysqld, Version: 5.5.39-log (MySQL Community Server (GPL)). started with:

Tcp port: 3306 Unix socket: /var/lib/mysql/mysql.sock
Time  Id Command Argument
141003 16:18:12 4 Query show variables like '%general%'
141003 16:18:55 4 Query select * from tempdb.tb1

b、更改通用查询日志位置

root@localhost[(none)]> exit

Bye
suse11b:~ # service mysql stop
Shutting down MySQL...   done
suse11b:~ # mysqld --general_log_file=/tmp/suse11b.log --user=mysql &
[1] 47009
suse11b:~ # ps -ef|grep mysql|grep -v grep
mysql 47009 44514 1 16:22 pts/0 00:00:00 mysqld --general_log_file=/tmp/suse11b.log --user=mysql
root 47053 44514 0 16:22 pts/0 00:00:00 grep mysql
suse11b:~ # mysql

root@localhost[(none)]> system ls /tmp/suse11b.log

ls: cannot access /tmp/suse11b.log: No such file or directory

root@localhost[(none)]> show variables like '%gener%';

+------------------+------------------+
| Variable_name | Value |
+------------------+------------------+
| general_log | OFF  |
| general_log_file | /tmp/suse11b.log |
+------------------+------------------+

root@localhost[(none)]> set global general_log=on;

Query OK, 0 rows affected (0.01 sec)

--此时从系统变量看出，通用日志已经到/tmp目录下
root@localhost[(none)]> show variables like '%gener%';

+------------------+------------------+
| Variable_name | Value |
+------------------+------------------+
| general_log | ON  |
| general_log_file | /tmp/suse11b.log |
+------------------+------------------+

--发布查询
root@localhost[(none)]> select count(*) from tempdb.tb1;

+----------+
| count(*) |
+----------+
| 1 |
+----------+

--查看通用日志文件内容
root@localhost[(none)]> system more /tmp/suse11b.log

mysqld, Version: 5.5.39-log (MySQL Community Server (GPL)). started with:
Tcp port: 3306 Unix socket: /var/lib/mysql/mysql.sock
Time  Id Command Argument
141003 16:30:03 1 Query show variables like '%gener%'
141003 16:30:09 1 Query select count(*) from tempdb.tb1

c、通用查询日志输出方式

--可以输出为文件，表以及不输出，即TABLE，FILE，NONE
--系统变量log_output
root@localhost[(none)]> show variables like 'log_output';

+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| log_output | FILE |
+---------------+-------+

--下面修改为输出为表方式
root@localhost[(none)]> set global log_output='TABLE';

Query OK, 0 rows affected (0.00 sec)

root@localhost[(none)]> show variables like 'log_output';

+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| log_output | TABLE |
+---------------+-------+

--发布查询
root@localhost[(none)]> select * from tempdb.tb1;

+------+------+
| id | val |
+------+------+
| 1 | jack |
+------+------+

root@localhost[(none)]> system more /tmp/suse11b.log

mysqld, Version: 5.5.39-log (MySQL Community Server (GPL)). started with:
Tcp port: 3306 Unix socket: /var/lib/mysql/mysql.sock
Time  Id Command Argument
141003 16:30:03 1 Query show variables like '%gener%'
141003 16:30:09 1 Query select count(*) from tempdb.tb1
141003 16:31:00 1 Query show variables like 'log_output'
141003 17:00:48 1 Query set global log_output='TABLE' #通用查询日志输出到文件仅仅记录到全局变量的修改

--mysql.general_log记录了通用查询日志的信息
root@localhost[(none)]> desc mysql.general_log;

+--------------+------------------+------+-----+-------------------+-----------------------------+
| Field | Type | Null | Key | Default  | Extra  |
+--------------+------------------+------+-----+-------------------+-----------------------------+
| event_time | timestamp | NO | | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
| user_host | mediumtext | NO | | NULL  |  |
| thread_id | int(11) | NO | | NULL  |  |
| server_id | int(10) unsigned | NO | | NULL  |  |
| command_type | varchar(64) | NO | | NULL  |  |
| argument | mediumtext | NO | | NULL  |  |
+--------------+------------------+------+-----+-------------------+-----------------------------+

--从通用查询日志表里查看通用查询日志的内容
root@localhost[(none)]> select thread_id,command_type,argument from mysql.general_log; 

+-----------+--------------+---------------------------------------------------------------+
| thread_id | command_type | argument    |
+-----------+--------------+---------------------------------------------------------------+
| 1 | Query | show variables like 'log_output'   |
| 1 | Query | select * from tempdb.tb1   |
| 1 | Query | desc mysql.general_log   |
| 1 | Query | select thread_id,command_type,argument from mysql.general_log |
+-----------+--------------+---------------------------------------------------------------+

root@localhost[(none)]> show variables like 'log_output';

+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| log_output | TABLE |
+---------------+-------+

--使用FILE,TABLE 2者混合输出通用日志
root@localhost[(none)]> set global log_output='file,table';

Query OK, 0 rows affected (0.00 sec)

root@localhost[(none)]> select @@global.log_output;

+---------------------+
| @@global.log_output |
+---------------------+
| FILE,TABLE |
+---------------------+

root@localhost[(none)]> insert into tempdb.tb1 values(2,'robinson');

Query OK, 1 row affected (0.06 sec)

root@localhost[(none)]> commit;

Query OK, 0 rows affected (0.01 sec)

--验证结果，表和文件里边存在通用的日志记录
root@localhost[(none)]> system tail /tmp/suse11b.log|grep robinson

141003 17:41:54 2 Query insert into tempdb.tb1 values(2,'robinson')

root@localhost[(none)]> select thread_id,command_type,argument from mysql.general_log
 -> where argument like '%robinson%';

+-----------+--------------+------------------------------------------------------------------------+
| thread_id | command_type | argument     |
+-----------+--------------+------------------------------------------------------------------------+
| 2 | Query | insert into tempdb.tb1 values(2,'robinson')  |
| 2 | Query | select thread_id,command_type,argument from mysql.general_log |
|  |  | where argument like ''robinson''   | 
+-----------+--------------+------------------------------------------------------------------------+

d、关闭通用查询日志

--可以通过设置系统变量general_log来关闭通用查询日志，此时日志输出设置为FILE,TABLE

root@localhost[(none)]> show variables like 'log_output';

+---------------+------------+
| Variable_name | Value |
+---------------+------------+
| log_output | FILE,TABLE |
+---------------+------------+

root@localhost[(none)]> set global general_log=off;

Query OK, 0 rows affected (0.01 sec)

root@localhost[(none)]> show variables like '%gener%';

+------------------+------------------+
| Variable_name | Value |
+------------------+------------------+
| general_log | OFF  |
| general_log_file | /tmp/suse11b.log |
+------------------+------------------+

root@localhost[(none)]> delete from tempdb.tb1 where id=2;

Query OK, 1 row affected (0.12 sec)

root@localhost[(none)]> commit;

Query OK, 0 rows affected (0.00 sec)

root@localhost[(none)]> system tail -n 1 /tmp/suse11b.log

141003 17:45:13 2 Query set global general_log=off

root@localhost[(none)]> select thread_id,command_type,argument from mysql.general_log
 -> where argument like '%delete%';

Empty set (0.00 sec)
--从上面的演示可知，尽管我们设置了log_output为FILE,TABLE，但general_log为OFF，通用日志无任何记录产生

root@localhost[(none)]> set global log_output=none;

Query OK, 0 rows affected (0.00 sec)

root@localhost[(none)]> set global general_log=1;

Query OK, 0 rows affected (0.00 sec)

root@localhost[(none)]> truncate table tempdb.tb1;

Query OK, 0 rows affected (0.01 sec)

root@localhost[(none)]> system tail -n 1 /tmp/suse11b.log

Time  Id Command Argument

--通过上面的演示，在log_output=none,general_log=on的清下下无任何通用日志输出。