mysql中的日志（一）

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如果你是一个Web开发人员，你需要参考各种日志文件，以调试应用程序或改善其性能。日志是故障排除的最佳手段。对于著名的MySQLdatabase服务器（或MariaDB服务器），你需要参考以下日志文件：

• The Error Log. 包含服务器运行时发生的错误信息（也服务器启动和停止）
• The General Query Log. 这是mysqld运行的常规记录（连接，断开连接，查询）
• The Slow Query Log. slow SQL statements

这篇文章并不是指二进制日志。它需要非常高的标准服务器硬件，只有在特殊情况下（如复制，主 - 从机设置，某些数据恢复操作）是非常有用的。 除此之外，它只是一个“性能杀手”。

关于MySQL日志的官方文档 here.

通过配置文件启用

配置参数在 [mysqld] 下面

 vim /etc/mysql/my.cnf

默认的配置文件 (in Debian server)

# * Logging and Replication
#
# Both location gets rotated by the cronjob.
# Be aware that this log type is a performance killer.
# As of 5.1 you can enable the log at runtime!
#general_log_file        = /var/log/mysql/mysql.log
#general_log             = 1
#
# Error logging goes to syslog due to /etc/mysql/conf.d/mysqld_safe_syslog.cnf.
#
# Here you can see queries with especially long duration
#log_slow_queries       = /var/log/mysql/mysql-slow.log
#long_query_time = 2
#log-queries-not-using-indexes
#
# The following can be used as easy to replay backup logs or for replication.
# note: if you are setting up a replication slave, see README.Debian about
#       other settings you may need to change.
#server-id              = 1
#log_bin                        = /var/log/mysql/mysql-bin.log
expire_logs_days        = 10
max_binlog_size         = 100M
#binlog_do_db           = include_database_name
#binlog_ignore_db       = include_database_name

默认情况下，所有的日志文件没有启用 (除了windows吓得错误日志). Default Debian setup sends Error log to syslog

Error Log

错误日志记录到syslog的情况，配置文件 /etc/mysql/conf.d/mysqld_safe_syslog.cnf

[mysqld_safe]
syslog

推荐的方式. 移除 /etc/mysql/conf.d/mysqld_safe_syslog.cnf  然后在 /etc/mysql/my.cnf 添加

[mysqld_safe]
log_error=/var/log/mysql/mysql_error.log
 
[mysqld]
log_error=/var/log/mysql/mysql_error.log

General Query Log

general_log_file        = /var/log/mysql/mysql.log
general_log             = 1

Slow Query Log

log_slow_queries       = /var/log/mysql/mysql-slow.log
long_query_time = 2
log-queries-not-using-indexes

Restart MySQL server after changes

service mysql restart

or, using systemd

systemctl restart mysql.service

运行时启用日志

从 MySQL 5.1 你可以禁用日志 at runtime.

启用日志, (mysql -u root -p ) 

SET GLOBAL general_log = ‘ON‘;
SET GLOBAL slow_query_log = ‘ON‘;

禁用日志, (mysql -u root -p )

SET GLOBAL general_log = ‘OFF‘;
SET GLOBAL slow_query_log = ‘OFF‘;

所有平台使用，无须重启

查看日志

Error log

注意: 如果你没有指定 Error log file, 默认在 (usually /var/lib/mysql in a file named {host_name}.err).

General Query log

注意: 如果你没有指定 General log file, 默认在 (usually /var/lib/mysqlin a file named {host_name}.log).

Slow Query log

注意: 如果你没有指定 Slow Query log file, 默认在 (usually/var/lib/mysql in a file named {host_name}-slow.log).

日志切割

不要忘记了切割日志.否则日志文件将会很大

In Debian (and Debian derivatives as Ubuntu etc) 

其他版本，可能需要一些改变

查看变量配置

TIP: Use show variables like ‘%log%‘; 检验日志文件

官方文档 here.

何时启用日志

默认情况下，所有的日志被禁用 (windows下的错误日志除外).Debian下默认讲错误日志写入 syslog.

事实上，没有什么情况下，日志能解决关键问题（这里还是英文来表示比较合适）

• 总是启用错误日志.
• 启用查询日志 (preferably at runtime) 当出现以下几种情况
  • check that your application handles correctly MySQL database connection (a common mistake is to connect multiple times to MySQL from a single script)
  • monitor executed queries from your application
  • test memcached (or similar software), checking out if a query was executed or memcached has handled the request
• 启用慢查询 (preferably from MySQL configuration file for a short period of time, e.g. 2-3 days) when your application performance is reduced for some reason and you should detect the slow queries.

示例

General query log:

原文：http://www.pontikis.net/blog/how-and-when-to-enable-mysql-logs

mysql中的日志（一）

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原文地址：http://www.cnblogs.com/chenpingzhao/p/4898609.html