故障解析丨一次死鎖問題的解決
作者：igoodful
根據binlog中部分SET @@SESSION.GTID_NEXT= 'e319a624-b2ce-11ee-9aac-00163e62ca8a:8697'該GTID的事務信息，可恢復T2，但T1執行的語句由于被回滾了，則不會記錄到binlog，可開啟general log日志獲取排查。
背景
業務端遇到報錯為"Deadlock found when trying to get lock; try restarting transaction"則表明有死鎖發生
名稱 | 配置 |
數據庫版本 | GreatSQL 8.0.26 |
隔離級別 | 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
------------查看表結構
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：
事務 | T1 | T2 |
操作 | insert into info values (50,11) | insert into info values (60,8) |
關聯的對象 | 表apple.info的唯一索引 uk_name | 表apple.info的唯一索引 uk_name |
持有的鎖 | lock mode S waitingheap no 7 11，40（十六進制為8，28） | lock_mode X locks rec but not gapheap no 7 11，40（十六進制為8，28） |
等待的鎖 | lock mode S waitingheap no 7 11，40（十六進制為8，28） | lock_mode X locks gap before rec insert intention waitingheap no 7 11，40（十六進制為8，28） |
- 首先事務T2獲取到了uk_name中記錄11的 lock x,rec not not gap 鎖
- 事務T1嘗試獲取uk_name中記錄11的lock s, next key lock，由于T2持有了記錄的獨占鎖，因此被T1堵塞
- 事務T2嘗試獲取uk_name中記錄11的lock x, gap before rec,insert intention，但被堵塞
獲取業務歷史SQL語句
通過系統表方式
通過performance_schema.threads、performance_schema.events_statements_history、performance_schema.events_statements_history_long等系統表獲取歷史SQL
- 根據GreatSQL thread id獲得線程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)- 根據線程id獲得線程歷史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)- 觀察show engine innodb status中的GreatSQL thread id 16和GreatSQL thread id 15
- 通過performance_schema.threads獲取THREAD_ID
- 通過performance_schema.events_statements_history獲取THREAD_ID執行的歷史SQL以及執行時間
最終可復現出如下業務SQL：
事務 | T1 | T2 |
語句 | begin; | begin; |
語句 | insert into info values (40,11); | |
語句 | insert into info values (50,11); | |
語句 | insert into info values (60,8); |
通過解析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*/;根據binlog中部分SET @@SESSION.GTID_NEXT= 'e319a624-b2ce-11ee-9aac-00163e62ca8a:8697'該GTID的事務信息，可恢復T2，但T1執行的語句由于被回滾了，則不會記錄到binlog，可開啟general log日志獲取排查
事務 | T1 | T2 |
語句 | begin; | begin; |
語句 | insert into info values (40,11); | |
語句 | insert into info values (50,11); | |
語句 | insert into info values (60,8); |
分析死鎖
- T1、T2開啟了一個事務
- 隨后T2執行了插入(40,11)的insert語句：insert into info values (40,11)
- T1執行了插入(50,11)的insert語句：insert into info values (50,11) 進行唯一性沖突檢查，嘗試獲取LOCK_S
- 然后T1所在的連接會將T2中的隱式鎖轉換為顯示鎖，此時T2將獲取Lock X, Rec_not_gap。由于T2的Lock X, Rec_not_gap與T1的LOCK S不兼容，因此T1被堵塞
- 隨后，T2又執行了(60,8)的insert語句：insert into info values (60,8) 由于其插入的唯一索引值是8，因此不存在主鍵沖突，直接執行樂觀插入操作。執行樂觀插入時，需要檢查其它事務是否堵塞insert操作。其核心是獲取待插入記錄的下一個值（這里剛好是10），并獲取該記錄上的所有鎖，與需要添加的鎖判斷是否存在沖突。
- T1持有了記錄11的LOCK_S鎖與T2的LOCK_X、LOCK_INSERT_INTENTION不兼容，因此T2被T1堵塞
- 死鎖形成。
解決
? 適當的減少Unique索引
? 避免插入重復的值（唯一索引所在列）
責任編輯：武曉燕
來源：
GreatSQL社區
