MySQL性能参数详解之Skip-External-Locking参数介绍

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MySQL性能参数详解之Skip-External-Locking参数介绍_MySQL

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May 27, 2016 pm 01:44 PM

MySQL的配置文件my.cnf中默认存在一行skip-external-locking的参数，即“跳过外部锁定”。根据MySQL开发网站的官方解释，External-locking用于多进程条件下为MyISAM数据表进行锁定。
如果你有多台服务器使用同一个数据库目录（不建议），那么每台服务器都必须开启external locking；

参数解释

当外部锁定（external-locking）起作用时，每个进程若要访问数据表，则必须等待之前的进程完成操作并解除锁定。由于服务器访问数据表时经常需要等待解锁，因此在单服务器环境下external locking会让MySQL性能下降。所以在很多Linux发行版的源中，MySQL配置文件中默认使用了skip-external-locking来避免external locking。
当使用了skip-external-locking后，为了使用MyISAMChk检查数据库或者修复、优化表，你必须保证在此过程中MySQL服务器没有使用需要操作的表。如果没有停止服务器，也至少需要先运行

代码如下:

mysqladmin flush-tables

命令，否则数据表可能出现异常。

参数使用说明
如果是多服务器环境，希望打开external locking特征，则注释掉这一行即可

代码如下:

# skip-external-locking

如果是单服务器环境，则将其禁用即可，使用如下语句

代码如下:

skip-external-locking

注意事项
在老版本的MySQL中，此参数的写法为：

代码如下:

skip-locking

如果在新版本MySQL配置中依然使用此写法，则可能出现：
[Warning] ‘–skip-locking' is deprecated and will be removed in a future release. Please use ‘–skip-external-locking' instead.
错误。

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