此语法对MySQL 5.6非常重要，在MySQL 5.6中，创建READ ONLY事务可避免InnoDB从内部设置许多结构.

This syntax was important for MySQL 5.6, where creating a READ ONLY transaction saved InnoDB from setting up a number of structures internally.

在MySQL 5.7中，优化得到了扩展，以便所有事务将从READ ONLY开始，然后根据需要转换为READ_WRITE. 此博客文章中对此进行了进一步描述.

In MySQL 5.7, the optimization was extended so that all transactions would start out READ ONLY and then convert to READ_WRITE as required. This is described further in this blog post.