MySQL Variables delay_key_write 数据库 参数变量解释及正确配置使用
本站中文解释
delay_key_write 参数表示用于指定在更新索引的时候是否延迟写入索引，默认选项是OFF，当有更新索引的数据变动时就立即将索引写入磁盘，此参数被设置为ON时会延迟索引的写入，即：在关闭服务器的时候才会将更新后的索引写入磁盘。
设置该参数的方法：
1. 使用MySQL客户端连接到MySQL服务器，选择要设置参数的数据库；
2. 执行如下SQL语句以设置 delay_key_write参数为ON：
SET GLOBAL delay_key_write = ON;
3. 设置成功即可。
官方英文解释
delay_key_write
| Command-Line Format | --delay-key-write[={OFF|ON|ALL}] |
|---|---|
| System Variable | delay_key_write |
| Scope | Global |
| Dynamic | Yes |
| Type | Enumeration |
| Default Value | ON |
| Valid Values |
|
This variable specifies how to use delayed key writes. It
applies only to MyISAM tables. Delayed key
writing causes key buffers not to be flushed between writes.
See also Section 15.2.1, “MyISAM Startup Options”.
This variable can have one of the following values to affect
handling of the DELAY_KEY_WRITE table
option that can be used in CREATE statements.
TABLE
| Option | Description |
|---|---|
OFF |
DELAY_KEY_WRITE is ignored. |
ON |
MySQL honors any DELAY_KEY_WRITE option specified inCREATE TABLE statements.This is the default value. |
ALL |
All new opened tables are treated as if they were created with theDELAY_KEY_WRITE option enabled. |
If you set this variable to ALL, you
should not use MyISAM tables from within
another program (such as another MySQL server or
myisamchk) when the tables are in use.
Doing so leads to index corruption.
If DELAY_KEY_WRITE is enabled for a table,
the key buffer is not flushed for the table on every index
update, but only when the table is closed. This speeds up
writes on keys a lot, but if you use this feature, you should
add automatic checking of all MyISAM tables
by starting the server with the
myisam_recover_options system
variable set (for example,
myisam_recover_options='BACKUP,FORCE').
See Section 5.1.7, “Server System Variables”, and
Section 15.2.1, “MyISAM Startup Options”.
If you start mysqld with
--skip-new,
delay_key_write is set to
OFF.
If you enable external locking with
--external-locking, there is
no protection against index corruption for tables that use
delayed key writes.
