锁理论

https://dev.mysql.com/doc/refman/5.6/en/innodb-locking.html

锁级别	锁名	锁模式	锁范围
表级别	读意向锁	lock mode IS
表级别	写意向锁	lock mode IX
行级别	读锁	lock S
行级别	写锁	lock X
行级别	行锁(单行)	lock_mode X locks rec but not gap	锁单行
行级别	GAP锁	lock_mode X locks gap before rec	间隙
行级别	next-key lock	lock_mode X	左开右闭
行级别	插入意向锁	lock_mode X locks gap before rec insert intention	间隙
表级锁	自增锁

 

 

 

select * from t ;   快照读，MVCC实现。
select  * from t lock in share mode; 当前读，lock S锁。

select ENGINE,THREAD_ID,EVENT_ID,OBJECT_SCHEMA,OBJECT_NAME,INDEX_NAME, LOCK_TYPE,LOCK_MODE ,LOCK_STATUS,LOCK_DATA from performance_schema.data_locks ;