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为什么MySQL引入Double Writer_MySQL

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Release： 2016-06-01 13:28:37
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为什么MySQL引入Double Writer
 

㈠ 是什么

   

   double writer是ibdata1(共享表空间)里面的一块连续空间

   BTW:为什么取名时叫buffer呢？难道一切缓冲写都叫buffer，加速读叫cache，哈哈

   

㈡ 为什么需要

   

   redo有效应用的前提是data的一致性，当data flush到磁盘时发生故障，比如16K只写了4K

   并且redo条目是change vector形式，属于逻辑记录，那么在InnoDB recovery时，redo就不知道从哪开始跑起

   简言之，就是为了解决部分写问题(partial page write)

   

㈢ 影响性能吗

   

   第一阶段，data写到double writer buffer属于顺序IO，节省IO开销

   第二阶段，因为double writer buffer积累了很多dirty page，再写向真正的位置时有可能合并，减少fsync()次数

   故，对性能影响不大

   

㈣ 相关参数

   

   ① show variables like '%double%';

   ② show status like '%innodb_dblwr%'; bitsCN.com

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