故障解析丨一次死锁问题的解决

* GreatSQL社区原创内容未经授权不得随意使用，转载请联系小编并注明来源。 背景 业务端遇到报错为"Deadlock found when trying to get lock; try restarting transaction"则表明有死锁发生 名称配置数据库版本GreatSQL 8.0.26隔离级别Read-Commited innodb status 日志 greatsql> show engine innodb status\G *************************** 1. row *************************** Type: InnoDB Name: Status: ===================================== 2024-01-28 16:55:38 140737023727360 INNODB MONITOR OUTPUT ===================================== Per second averages calculated from the last 14 seconds ----------------- BACKGROUND THREAD ----------------- srv_master_thread loops: 41 srv_active, 0 srv_shutdown, 17830 srv_idle srv_master_thread log flush and writes: 0 ---------- SEMAPHORES ---------- ------------- RW-LATCH INFO ------------- Total number of rw-locks 132361 OS WAIT ARRAY INFO: reservation count 11180 OS WAIT ARRAY INFO: signal count 11177 RW-shared spins 0, rounds 0, OS waits 0 RW-excl spins 0, rounds 0, OS waits 0 RW-sx spins 0, rounds 0, OS waits 0 Spin rounds per wait: 0.00 RW-shared, 0.00 RW-excl, 0.00 RW-sx ------------------------ LATEST DETECTED DEADLOCK ------------------------ 2024-01-28 16:53:40 140735053358848 *** (1) TRANSACTION: TRANSACTION 37616, ACTIVE 8 sec inserting mysql tables in use 1, locked 1 LOCK WAIT 2 lock struct(s), heap size 1192, 1 row lock(s), undo log entries 1 MySQL thread id 16, OS thread handle 140737023432448, query id 652 127.0.0.1 root update insert into info values (50,11) *** (1) HOLDS THE LOCK(S): RECORD LOCKS space id 26 page no 5 n bits 80 index uk_name of table `apple`.`info` trx id 37616 lock mode S waiting Record lock, heap no 7 PHYSICAL RECORD: n_fields 2; compact format; info bits 0 0: len 4; hex 8000000b; asc ;; 1: len 4; hex 80000028; asc (;; *** (1) WAITING FOR THIS LOCK TO BE GRANTED: RECORD LOCKS space id 26 page no 5 n bits 80 index uk_name of table `apple`.`info` trx id 37616 lock mode S waiting Record lock, heap no 7 PHYSICAL RECORD: n_fields 2; compact format; info bits 0 0: len 4; hex 8000000b; asc ;; 1: len 4; hex 80000028; asc (;; *** (2) TRANSACTION: TRANSACTION 37615, ACTIVE 24 sec inserting mysql tables in use 1, locked 1 LOCK WAIT 3 lock struct(s), heap size 1192, 2 row lock(s), undo log entries 2 MySQL thread id 15, OS thread handle 140737024022272, query id 653 127.0.0.1 root update insert into info values (60,8) *** (2) HOLDS THE LOCK(S): RECORD LOCKS space id 26 page no 5 n bits 80 index uk_name of table `apple`.`info` trx id 37615 lock_mode X locks rec but not gap Record lock, heap no 7 PHYSICAL RECORD: n_fields 2; compact format; info bits 0 0: len 4; hex 8000000b; asc ;; 1: len 4; hex 80000028; asc (;; *** (2) WAITING FOR THIS LOCK TO BE GRANTED: RECORD LOCKS space id 26 page no 5 n bits 80 index uk_name of table `apple`.`info` trx id 37615 lock_mode X locks gap before rec insert intention waiting Record lock, heap no 7 PHYSICAL RECORD: n_fields 2; compact format; info bits 0 0: len 4; hex 8000000b; asc ;; 1: len 4; hex 80000028; asc (;; *** WE ROLL BACK TRANSACTION (1) ------------ TRANSACTIONS ------------ 查看表结构 greatsql> show create table info \G *************************** 1. row *************************** Table: info Create Table: CREATE TABLE `info` ( `id` int NOT NULL AUTO_INCREMENT, `name` int NOT NULL, PRIMARY KEY (`id`), UNIQUE KEY `uk_name` (`name`) ) ENGINE=InnoDB AUTO_INCREMENT=61 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci 1 row in set (0.01 sec) 梳理 innodb status 日志

• 整理如下：

事务T1T2操作insert into info values (50,11)insert into info values (60,8)关联的对象表apple.info的唯一索引 uk_name表apple.info的唯一索引 uk_name持有的锁lock mode S waitingheap no 7 11，40（十六进制为8，28）lock_mode X locks rec but not gapheap no 7 11，40（十六进制为8，28）等待的锁lock mode S waitingheap no 7 11，40（十六进制为8，28）lock_mode X locks gap before rec insert intention waitingheap no 7 11，40（十六进制为8，28）

• 首先事务T2获取到了uk_name中记录11的 lock x,rec not not gap 锁
• 事务T1尝试获取uk_name中记录11的lock s, next key lock，由于T2持有了记录的独占锁，因此被T1堵塞
• 事务T2尝试获取uk_name中记录11的lock x, gap before rec,insert intention，但被堵塞

获取业务历史SQL语句 通过系统表方式 通过performance_schema.threads、performance_schema.events_statements_history、performance_schema.events_statements_history_long等系统表获取历史SQL

• 根据GreatSQL thread id获得线程id

greatsql> select PROCESSLIST_ID,THREAD_ID,THREAD_OS_ID from performance_schema.threads where processlist_id in (15,16); +----------------+-----------+--------------+ | PROCESSLIST_ID | THREAD_ID | THREAD_OS_ID | +----------------+-----------+--------------+ | 15 | 61 | 5714 | | 16 | 62 | 5719 | +----------------+-----------+--------------+ 2 rows in set (0.00 sec)

• 根据线程id获得线程历史SQL

greatsql> select THREAD_ID,EVENT_ID,CURRENT_SCHEMA,SQL_TEXT,MESSAGE_TEXT,EVENT_NAME,SOURCE from performance_schema.events_statements_history where thread_id in (61,62) order by THREAD_ID,EVENT_ID; +-----------+----------+----------------+---------------------------------+--------------------------------------------------------------------+--------------------------+---------------------------------+ | THREAD_ID | EVENT_ID | CURRENT_SCHEMA | SQL_TEXT | MESSAGE_TEXT | EVENT_NAME | SOURCE | +-----------+----------+----------------+---------------------------------+--------------------------------------------------------------------+--------------------------+---------------------------------+ | 61 | 3762 | apple | NULL | NULL | statement/com/Field List | init_net_server_extension.cc:94 | | 61 | 3807 | apple | NULL | NULL | statement/com/Field List | init_net_server_extension.cc:94 | | 61 | 3852 | apple | NULL | NULL | statement/com/Field List | init_net_server_extension.cc:94 | | 61 | 3897 | apple | NULL | NULL | statement/com/Field List | init_net_server_extension.cc:94 | | 61 | 3942 | apple | NULL | NULL | statement/com/Field List | init_net_server_extension.cc:94 | | 61 | 3987 | apple | NULL | NULL | statement/com/Field List | init_net_server_extension.cc:94 | | 61 | 4032 | apple | NULL | NULL | statement/com/Field List | init_net_server_extension.cc:94 | | 61 | 4077 | apple | begin | NULL | statement/sql/begin | init_net_server_extension.cc:94 | | 61 | 4100 | apple | insert into info values (40,11) | NULL | statement/sql/insert | init_net_server_extension.cc:94 | | 61 | 4569 | apple | insert into info values (60,8) | NULL | statement/sql/insert | init_net_server_extension.cc:94 | | 62 | 3215 | apple | NULL | NULL | statement/com/Field List | init_net_server_extension.cc:94 | | 62 | 3260 | apple | NULL | NULL | statement/com/Field List | init_net_server_extension.cc:94 | | 62 | 3305 | apple | NULL | NULL | statement/com/Field List | init_net_server_extension.cc:94 | | 62 | 3350 | apple | NULL | NULL | statement/com/Field List | init_net_server_extension.cc:94 | | 62 | 3395 | apple | NULL | NULL | statement/com/Field List | init_net_server_extension.cc:94 | | 62 | 3440 | apple | NULL | NULL | statement/com/Field List | init_net_server_extension.cc:94 | | 62 | 3485 | apple | NULL | NULL | statement/com/Field List | init_net_server_extension.cc:94 | | 62 | 3530 | apple | NULL | NULL | statement/com/Field List | init_net_server_extension.cc:94 | | 62 | 3575 | apple | begin | NULL | statement/sql/begin | init_net_server_extension.cc:94 | | 62 | 3598 | apple | insert into info values (50,11) | Deadlock found when trying to get lock; try restarting transaction | statement/sql/insert | init_net_server_extension.cc:94 | +-----------+----------+----------------+---------------------------------+--------------------------------------------------------------------+--------------------------+---------------------------------+ 20 rows in set (0.00 sec)

• 观察show engine innodb status中的GreatSQL thread id 16和GreatSQL thread id 15
• 通过performance_schema.threads获取THREAD_ID
• 通过performance_schema.events_statements_history获取THREAD_ID执行的历史SQL以及执行时间

最终可复现出如下业务SQL： 事务T1T2语句begin;begin;语句 insert into info values (40,11);语句insert into info values (50,11); 语句 insert into info values (60,8); 通过解析binlog $ mysqlbinlog -vv --base64-output=decode-rows bin.000030 SET @@SESSION.GTID_NEXT= 'e319a624-b2ce-11ee-9aac-00163e62ca8a:8696'/*!*/; # at 10314 #240128 16:52:35 server id 1024 end_log_pos 10390 CRC32 0x59edb313 Query thread_id=18 exec_time=0 error_code=0 SET TIMESTAMP=1706431955/*!*/; BEGIN /*!*/; # at 10390 #240128 16:52:35 server id 1024 end_log_pos 10442 CRC32 0xc03dea61 Table_map: `apple`.`info` mapped to number 370 # at 10442 #240128 16:52:35 server id 1024 end_log_pos 10486 CRC32 0x670e0c66 Write_rows: table id 370 flags: STMT_END_F ### INSERT INTO `apple`.`info` ### SET ### @1=30 /* INT meta=0 nullable=0 is_null=0 */ ### @2=30 /* INT meta=0 nullable=0 is_null=0 */ # at 10486 #240128 16:52:35 server id 1024 end_log_pos 10517 CRC32 0xab4e0d89 Xid = 598 COMMIT/*!*/; # at 10517 #240128 19:22:12 server id 1024 end_log_pos 10596 CRC32 0x4f4cf08e GTID last_committed=30 sequence_number=36 rbr_only=yes original_committed_timestamp=1706440932450590 immediate_commit_timestamp=1706440932450590 transaction_length=378 /*!50718 SET TRANSACTION ISOLATION LEVEL READ COMMITTED*//*!*/; # original_commit_timestamp=1706440932450590 (2024-01-28 19:22:12.450590 CST) # immediate_commit_timestamp=1706440932450590 (2024-01-28 19:22:12.450590 CST) /*!80001 SET @@session.original_commit_timestamp=1706440932450590*//*!*/; /*!80014 SET @@session.original_server_version=80026*//*!*/; /*!80014 SET @@session.immediate_server_version=80026*//*!*/; SET @@SESSION.GTID_NEXT= 'e319a624-b2ce-11ee-9aac-00163e62ca8a:8697'/*!*/; # at 10596 #240128 16:53:16 server id 1024 end_log_pos 10672 CRC32 0xf222c003 Query thread_id=15 exec_time=0 error_code=0 SET TIMESTAMP=1706431996/*!*/; BEGIN /*!*/; # at 10672 #240128 16:53:16 server id 1024 end_log_pos 10724 CRC32 0x20cb8c86 Table_map: `apple`.`info` mapped to number 370 # at 10724 #240128 16:53:16 server id 1024 end_log_pos 10768 CRC32 0xd8f53958 Write_rows: table id 370 flags: STMT_END_F ### INSERT INTO `apple`.`info` ### SET ### @1=40 /* INT meta=0 nullable=0 is_null=0 */ ### @2=11 /* INT meta=0 nullable=0 is_null=0 */ # at 10768 #240128 16:53:40 server id 1024 end_log_pos 10820 CRC32 0x23f22580 Table_map: `apple`.`info` mapped to number 370 # at 10820 #240128 16:53:40 server id 1024 end_log_pos 10864 CRC32 0x182ecdef Write_rows: table id 370 flags: STMT_END_F ### INSERT INTO `apple`.`info` ### SET ### @1=60 /* INT meta=0 nullable=0 is_null=0 */ ### @2=8 /* INT meta=0 nullable=0 is_null=0 */ # at 10864 #240128 19:22:12 server id 1024 end_log_pos 10895 CRC32 0x57fd1d3c Xid = 650 COMMIT/*!*/; SET @@SESSION.GTID_NEXT= 'AUTOMATIC' /* added by mysqlbinlog */ /*!*/; DELIMITER ; # End of log file /*!50003 SET COMPLETION_TYPE=@OLD_COMPLETION_TYPE*/; /*!50530 SET @@SESSION.PSEUDO_SLAVE_MODE=0*/; 根据binlog中部分SET @@SESSION.GTID_NEXT= 'e319a624-b2ce-11ee-9aac-00163e62ca8a:8697'该GTID的事务信息，可恢复T2，但T1执行的语句由于被回滚了，则不会记录到binlog，可开启general log日志获取排查 事务T1T2语句begin;begin;语句 insert into info values (40,11);语句insert into info values (50,11); 语句 insert into info values (60,8); 分析死锁

• T1、T2开启了一个事务
• 随后T2执行了插入(40,11)的insert语句：insert into info values (40,11)
• T1执行了插入(50,11)的insert语句：insert into info values (50,11) 进行唯一性冲突检查，尝试获取LOCK_S
• 然后T1所在的连接会将T2中的隐式锁转换为显示锁，此时T2将获取Lock X, Rec_not_gap。由于T2的Lock X, Rec_not_gap与T1的LOCK S不兼容，因此T1被堵塞
• 随后，T2又执行了(60,8)的insert语句：insert into info values (60,8) 由于其插入的唯一索引值是8，因此不存在主键冲突，直接执行乐观插入操作。执行乐观插入时，需要检查其它事务是否堵塞insert操作。其核心是获取待插入记录的下一个值（这里刚好是10），并获取该记录上的所有锁，与需要添加的锁判断是否存在冲突。
• T1持有了记录11的LOCK_S锁与T2的LOCK_X、LOCK_INSERT_INTENTION不兼容，因此T2被T1堵塞
• 死锁形成。

解决 • 适当的减少Unique索引 • 避免插入重复的值（唯一索引所在列）