浅析My sql事务隔离级别与锁 seanlook
1 like445 views
This document discusses InnoDB locking mechanisms in MySQL, including: - Row-level locks are used to prevent conflicts between transactions accessing the same rows. - Different isolation levels determine which types of locks are used and what kinds of conflicts are allowed. Read committed is the default isolation level. - Deadlocks can occur when multiple transactions try to acquire locks in incompatible orders. InnoDB detects and rolls back transactions involved in deadlocks.
浅析My sql事务隔离级别与锁 seanlook
- 3. 会锁定多少行记录？ CREATE TABLE `t` ( `f_id` int(11) AUTO_INCREMENT NOT NULL, `f_name` varchar(30) NOT NULL DEFAULT ‘’, `f_group` tinyint(3) unsigned, PRIMARY KEY (`f_id`), UNIQUE KEY `idx_name` (`f_name`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8;
- 6. session A session B BEGIN WORK BEGIN WORK select count(*) update a record InnoDB Lock Compatity S X IS IX S 兼容 不兼容 兼容 不兼容 X 不兼容 不兼容 不兼容 不兼容 IS 兼容 不兼容 兼容 兼容 IX 不兼容 不兼容 兼容 兼容
- 7. 两段封锁法 SELECT * FROM t where f_id=1 SELECT * FROM t where f_id=1 FOR update SELECT * FROM t where f_id>10 LOCK IN share mode insert into table values (…) update table set ? where ? delete from table where ?
- 9. (buffer) (LSN) (顺序IO) • 2 Phase Commit • innodb_flush_log_at_trx_commit • sync_binlog UNDO -> 原子性 REDO -> 永久性 Lock+Undo -> 隔离性 Constraint -> 一致性
- 11. (MVCC) 1 a 0001 0x123456 018 f_id f_name f_age DATA_TRX_ID DATA_ROLL_PTR DELETE_BIT undo log 100 trx_1 1 aa 0002 0x234567 018 undo log 101 undo log 100 trx_2
- 12. 读未提交 (Read Uncommitted) YES YES YES 已提交读 (Read Committed) NO YES YES 可重复读 (Repeatable Read) NO NO YES ? 可串行化 (Serializable) NO NO NO (default for RDS) (default for Official) 隔离级别 脏读 (Dirty Read) 不可重复读 (Non-Repeatable Read) 幻读 (Phantom Read)
- 13. session A session B 1 START TRANSACTION START TRANSACTION 2 select * from t where f_id>0 and f_id<5; 3 update t set f_name='aa' where f_id=1; 4 insert into t values(3,'c'); 5 select * from t where f_id>0 and f_id<5; 6 COMMIT 7 select * from t where f_id>0 and f_id<5; 8 COMMIT 9 select * from t where f_id>0 and f_id<5; 分别在RC和RR级别下执行
- 14. session A session B 1 START TRANSACTION START TRANSACTION 2 select * from t where f_group>10 and f_gender=1 for update; 3 update t set f_gender=0 where f_id=99; 分别在RC和RR级别下执行 RC: 0 rows affected RR: blocked
- 15. delete from t1 where id = 10;
- 16. RR session A session B 1 START TRANSACTION START TRANSACTION 2 update t set f_group=0 where f_group < 20 3 insert into t values(111,'10K',18); 4 commit
- 18. session A session B session C 1 START TRANSACTION START TRANSACTION START TRANSACTION 2 INSERT INTO t (f_name) VALUES (‘cc'); 3 INSERT INTO t (f_name) VALUES (‘cc'); 4 INSERT INTO t (f_name) VALUES (‘cc'); 5 rollback ERROR 1213 (40001): Deadlock found when trying to get lock; try restarting transaction