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Snailclimb merged 1 commit into from
Feb 17, 2023
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Update mysql-questions-01.md #1925

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2 changes: 1 addition & 1 deletion docs/database/mysql/mysql-questions-01.md
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Expand Up @@ -402,7 +402,7 @@ MySQL 中并发事务的控制方式无非就两种：**锁** 和 **MVCC**。锁
**锁** 控制方式下会通过锁来显示控制共享资源而不是通过调度手段，MySQL 中主要是通过 **读写锁** 来实现并发控制。

- **共享锁（S 锁）** ：又称读锁，事务在读取记录的时候获取共享锁，允许多个事务同时获取（锁兼容）。
- **排他锁（X 锁）** ：又称写锁/独占锁，事务在修改记录的时候获取排他锁，不允许多个事务同时获取。如果一个记录已经被加了排他锁，那其他事务不能再对这条事务加任何类型的锁（锁不兼容）。
- **排他锁（X 锁）** ：又称写锁/独占锁，事务在修改记录的时候获取排他锁，不允许多个事务同时获取。如果一个记录已经被加了排他锁，那其他事务不能再对这条记录加任何类型的锁（锁不兼容）。

读写锁可以做到读读并行，但是无法做到写读、写写并行。另外，根据根据锁粒度的不同，又被分为 **表级锁(table-level locking)** 和 **行级锁(row-level locking)** 。InnoDB 不光支持表级锁，还支持行级锁，默认为行级锁。行级锁的粒度更小，仅对相关的记录上锁即可（对一行或者多行记录加锁），所以对于并发写入操作来说， InnoDB 的性能更高。不论是表级锁还是行级锁，都存在共享锁（Share Lock，S 锁）和排他锁（Exclusive Lock，X 锁）这两类。

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