baiwfg2
commented
2 years ago lock
http://mysql.taobao.org/monthly/2020/04/02
增加SX 锁，SX模式是对X模式的一种优化，它与读操作的S模式兼容，但是多个SX锁之间是冲突的。
InnoDB读写锁实现的核心思想是避免使用pthread rwlock，而尽量使用原子操作+自旋的模式来实现加解锁，这样可以在低冲突的场景下，以尽量小的开销实现加解锁。遇到实在是冲突高的读写锁，再使用InnoDB条件变量实现等待。
InnoDB读写锁上的X锁所有权是可以在不同线程间转移的，主要用于支持Change Buffer的场景。Change Buffer是一棵全局共享的B+树，存储在系统表空间中。在读取二级索引Page的时候Change Buffer需要与二级索引Page进行合并，这时如果所有IO线程都在读取二级索引Page，将没有IO线程读取Change Buffer Page，因此Change Buffer Page的读取被放到单独的IO线程。而读取二级索引Page的时候，已经对Page加上了X锁，当在异步IO线程需要把Change Buffer合并到二级索引的Page的时候，必须在不解锁的情况下让异步线程获得Page的X锁，这就是X锁所有权转移需要实现的功能
rw_lock_t, rw_lock_x_lock_func , rw_lock_x_unlock_func, rw_lock_x_lock_move_ownership
有加解锁的流程图
innodb mutex
事务锁
https://zhuanlan.zhihu.com/p/414816343 ， 行锁分析
https://dev.mysql.com/doc/refman/8.0/en/innodb-locking.html
It is also worth noting here that conflicting locks can be held on a gap by different transactions. For example, transaction A can hold a shared gap lock (gap S-lock) on a gap while transaction B holds an exclusive gap lock (gap X-lock) on the same gap. The reason conflicting gap locks are allowed is that if a record is purged from an index, the gap locks held on the record by different transactions must be merged.
https://severalnines.com/blog/understanding-lock-granularity-mysql/ mysql 以前支持BDB，它有page-level locking
row-level locking has disadvantages too: one of them is that row-level locking usually takes up more memory than page-level or table-level locking, it’s also usually slower than page-level or table-level locks because the engine must acquire more locks
taobao mysql
https://blog.csdn.net/u011385940/article/details/120206427 taobao mysql 文章列表
test
可编 m_string-t dd_cache_t