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The following example illustrates how an error can occur when a lock request causes a deadlock. The example involves two clients, A and B.

InnoDB status contains details of the last deadlock. For frequent deadlocks, enable global variableinnodb_print_all_deadlocks. This adds deadlock information to the error log.

Client A enablesinnodb_print_all_deadlocks, creates two tables, 'Animals' and 'Birds', and inserts data into each. Client A begins a transaction, and selects a row in Animals in share mode:

mysql> SET GLOBAL innodb_print_all_deadlocks = ON;Query OK, 0 rows affected (0.00 sec)mysql> CREATE TABLE Animals (name VARCHAR(10) PRIMARY KEY, value INT) ENGINE = InnoDB;Query OK, 0 rows affected (0.01 sec)mysql> CREATE TABLE Birds (name VARCHAR(10) PRIMARY KEY, value INT) ENGINE = InnoDB;Query OK, 0 rows affected (0.01 sec)mysql> INSERT INTO Animals (name,value) VALUES ("Aardvark",10);Query OK, 1 row affected (0.00 sec)mysql> INSERT INTO Birds (name,value) VALUES ("Buzzard",20);Query OK, 1 row affected (0.00 sec)mysql> START TRANSACTION;Query OK, 0 rows affected (0.00 sec)mysql> SELECT value FROM Animals WHERE name='Aardvark' FOR SHARE;+-------+| value |+-------+|    10 |+-------+1 row in set (0.00 sec)

Next, client B begins a transaction, and selects a row in Birds in share mode:

mysql> START TRANSACTION;Query OK, 0 rows affected (0.00 sec)mysql> SELECT value FROM Birds WHERE name='Buzzard' FOR SHARE;+-------+| value |+-------+|    20 |+-------+1 row in set (0.00 sec)

The Performance Schema shows the locks after the two select statements:

mysql> SELECT ENGINE_TRANSACTION_ID as Trx_Id,    ->     OBJECT_NAME as `Table`,     ->     INDEX_NAME as `Index`,     ->     LOCK_DATA as Data,     ->     LOCK_MODE as Mode,     ->     LOCK_STATUS as Status,     ->     LOCK_TYPE as Type     -> FROM performance_schema.data_locks;+-----------------+---------+---------+------------+---------------+---------+--------+| Trx_Id          | Table   | Index   | Data       | Mode          | Status  | Type   |+-----------------+---------+---------+------------+---------------+---------+--------+| 421291106147544 | Animals | NULL    | NULL       | IS            | GRANTED | TABLE  || 421291106147544 | Animals | PRIMARY | 'Aardvark' | S,REC_NOT_GAP | GRANTED | RECORD || 421291106148352 | Birds   | NULL    | NULL       | IS            | GRANTED | TABLE  || 421291106148352 | Birds   | PRIMARY | 'Buzzard'  | S,REC_NOT_GAP | GRANTED | RECORD |+-----------------+---------+---------+------------+---------------+---------+--------+4 rows in set (0.00 sec)

Client B then updates a row in Animals:

mysql> UPDATE Animals SET value=30 WHERE name='Aardvark';

Client B has to wait. The Performance Schema shows the wait for a lock:

mysql> SELECT REQUESTING_ENGINE_LOCK_ID as Req_Lock_Id,    ->     REQUESTING_ENGINE_TRANSACTION_ID as Req_Trx_Id,    ->     BLOCKING_ENGINE_LOCK_ID as Blk_Lock_Id,     ->     BLOCKING_ENGINE_TRANSACTION_ID as Blk_Trx_Id    -> FROM performance_schema.data_lock_waits;+----------------------------------------+------------+----------------------------------------+-----------------+| Req_Lock_Id                            | Req_Trx_Id | Blk_Lock_Id                            | Blk_Trx_Id      |+----------------------------------------+------------+----------------------------------------+-----------------+| 139816129437696:27:4:2:139816016601240 |      43260 | 139816129436888:27:4:2:139816016594720 | 421291106147544 |+----------------------------------------+------------+----------------------------------------+-----------------+1 row in set (0.00 sec)mysql> SELECT ENGINE_LOCK_ID as Lock_Id,     ->     ENGINE_TRANSACTION_ID as Trx_id,     ->     OBJECT_NAME as `Table`,     ->     INDEX_NAME as `Index`,     ->     LOCK_DATA as Data,     ->     LOCK_MODE as Mode,     ->     LOCK_STATUS as Status,     ->     LOCK_TYPE as Type     -> FROM performance_schema.data_locks;+----------------------------------------+-----------------+---------+---------+------------+---------------+---------+--------+| Lock_Id                                | Trx_Id          | Table   | Index   | Data       | Mode          | Status  | Type   |+----------------------------------------+-----------------+---------+---------+------------+---------------+---------+--------+| 139816129437696:1187:139816016603896   |           43260 | Animals | NULL    | NULL       | IX            | GRANTED | TABLE  || 139816129437696:1188:139816016603808   |           43260 | Birds   | NULL    | NULL       | IS            | GRANTED | TABLE  || 139816129437696:28:4:2:139816016600896 |           43260 | Birds   | PRIMARY | 'Buzzard'  | S,REC_NOT_GAP | GRANTED | RECORD || 139816129437696:27:4:2:139816016601240 |           43260 | Animals | PRIMARY | 'Aardvark' | X,REC_NOT_GAP | WAITING | RECORD || 139816129436888:1187:139816016597712   | 421291106147544 | Animals | NULL    | NULL       | IS            | GRANTED | TABLE  || 139816129436888:27:4:2:139816016594720 | 421291106147544 | Animals | PRIMARY | 'Aardvark' | S,REC_NOT_GAP | GRANTED | RECORD |+----------------------------------------+-----------------+---------+---------+------------+---------------+---------+--------+6 rows in set (0.00 sec)

InnoDB only uses sequential transaction ids when a transaction attempts to modify the database. Thererfore, the previous read-only transaction id changes from 421291106148352 to 43260.

If client A attempts to update a row in Birds at the same time, this will lead to a deadlock:

mysql> UPDATE Birds SET value=40 WHERE name='Buzzard';ERROR 1213 (40001): Deadlock found when trying to get lock; try restarting transaction

InnoDB rolls back the transaction that caused the deadlock. The first update, from Client B, can now proceed.

The Information Schema contains the number of deadlocks:

mysql> SELECT `count` FROM INFORMATION_SCHEMA.INNODB_METRICS          WHERE NAME="lock_deadlocks";+-------+| count |+-------+|     1 |+-------+1 row in set (0.00 sec)

The InnoDB status contains the following information about the deadlock and transactions. It also shows that the read-only transaction id 421291106147544 changes to sequential transaction id 43261.

mysql> SHOW ENGINE INNODB STATUS;------------------------LATEST DETECTED DEADLOCK------------------------2022-11-25 15:58:22 139815661168384*** (1) TRANSACTION:TRANSACTION 43260, ACTIVE 186 sec starting index readmysql tables in use 1, locked 1LOCK WAIT 4 lock struct(s), heap size 1128, 2 row lock(s)MySQL thread id 19, OS thread handle 139815619204864, query id 143 localhost u2 updatingUPDATE Animals SET value=30 WHERE name='Aardvark'*** (1) HOLDS THE LOCK(S):RECORD LOCKS space id 28 page no 4 n bits 72 index PRIMARY of table `test`.`Birds` trx id 43260 lock mode S locks rec but not gapRecord lock, heap no 2 PHYSICAL RECORD: n_fields 4; compact format; info bits 0 0: len 7; hex 42757a7a617264; asc Buzzard;; 1: len 6; hex 00000000a8fb; asc       ;; 2: len 7; hex 82000000e40110; asc        ;; 3: len 4; hex 80000014; asc     ;;*** (1) WAITING FOR THIS LOCK TO BE GRANTED:RECORD LOCKS space id 27 page no 4 n bits 72 index PRIMARY of table `test`.`Animals` trx id 43260 lock_mode X locks rec but not gap waitingRecord lock, heap no 2 PHYSICAL RECORD: n_fields 4; compact format; info bits 0 0: len 8; hex 416172647661726b; asc Aardvark;; 1: len 6; hex 00000000a8f9; asc       ;; 2: len 7; hex 82000000e20110; asc        ;; 3: len 4; hex 8000000a; asc     ;;*** (2) TRANSACTION:TRANSACTION 43261, ACTIVE 209 sec starting index readmysql tables in use 1, locked 1LOCK WAIT 4 lock struct(s), heap size 1128, 2 row lock(s)MySQL thread id 18, OS thread handle 139815618148096, query id 146 localhost u1 updatingUPDATE Birds SET value=40 WHERE name='Buzzard'*** (2) HOLDS THE LOCK(S):RECORD LOCKS space id 27 page no 4 n bits 72 index PRIMARY of table `test`.`Animals` trx id 43261 lock mode S locks rec but not gapRecord lock, heap no 2 PHYSICAL RECORD: n_fields 4; compact format; info bits 0 0: len 8; hex 416172647661726b; asc Aardvark;; 1: len 6; hex 00000000a8f9; asc       ;; 2: len 7; hex 82000000e20110; asc        ;; 3: len 4; hex 8000000a; asc     ;;*** (2) WAITING FOR THIS LOCK TO BE GRANTED:RECORD LOCKS space id 28 page no 4 n bits 72 index PRIMARY of table `test`.`Birds` trx id 43261 lock_mode X locks rec but not gap waitingRecord lock, heap no 2 PHYSICAL RECORD: n_fields 4; compact format; info bits 0 0: len 7; hex 42757a7a617264; asc Buzzard;; 1: len 6; hex 00000000a8fb; asc       ;; 2: len 7; hex 82000000e40110; asc        ;; 3: len 4; hex 80000014; asc     ;;*** WE ROLL BACK TRANSACTION (2)------------TRANSACTIONS------------Trx id counter 43262Purge done for trx's n:o < 43256 undo n:o < 0 state: running but idleHistory list length 0LIST OF TRANSACTIONS FOR EACH SESSION:---TRANSACTION 421291106147544, not started0 lock struct(s), heap size 1128, 0 row lock(s)---TRANSACTION 421291106146736, not started0 lock struct(s), heap size 1128, 0 row lock(s)---TRANSACTION 421291106145928, not started0 lock struct(s), heap size 1128, 0 row lock(s)---TRANSACTION 43260, ACTIVE 219 sec4 lock struct(s), heap size 1128, 2 row lock(s), undo log entries 1MySQL thread id 19, OS thread handle 139815619204864, query id 143 localhost u2

The error log contains this information about transactions and locks:

mysql> SELECT @@log_error;+---------------------+| @@log_error         |+---------------------+| /var/log/mysqld.log |+---------------------+1 row in set (0.00 sec)TRANSACTION 43260, ACTIVE 186 sec starting index readmysql tables in use 1, locked 1LOCK WAIT 4 lock struct(s), heap size 1128, 2 row lock(s)MySQL thread id 19, OS thread handle 139815619204864, query id 143 localhost u2 updatingUPDATE Animals SET value=30 WHERE name='Aardvark'RECORD LOCKS space id 28 page no 4 n bits 72 index PRIMARY of table `test`.`Birds` trx id 43260 lock mode S locks rec but not gapRecord lock, heap no 2 PHYSICAL RECORD: n_fields 4; compact format; info bits 0 0: len 7; hex 42757a7a617264; asc Buzzard;; 1: len 6; hex 00000000a8fb; asc       ;; 2: len 7; hex 82000000e40110; asc        ;; 3: len 4; hex 80000014; asc     ;;RECORD LOCKS space id 27 page no 4 n bits 72 index PRIMARY of table `test`.`Animals` trx id 43260 lock_mode X locks rec but not gap waitingRecord lock, heap no 2 PHYSICAL RECORD: n_fields 4; compact format; info bits 0 0: len 8; hex 416172647661726b; asc Aardvark;; 1: len 6; hex 00000000a8f9; asc       ;; 2: len 7; hex 82000000e20110; asc        ;; 3: len 4; hex 8000000a; asc     ;;TRANSACTION 43261, ACTIVE 209 sec starting index readmysql tables in use 1, locked 1LOCK WAIT 4 lock struct(s), heap size 1128, 2 row lock(s)MySQL thread id 18, OS thread handle 139815618148096, query id 146 localhost u1 updatingUPDATE Birds SET value=40 WHERE name='Buzzard'RECORD LOCKS space id 27 page no 4 n bits 72 index PRIMARY of table `test`.`Animals` trx id 43261 lock mode S locks rec but not gapRecord lock, heap no 2 PHYSICAL RECORD: n_fields 4; compact format; info bits 0 0: len 8; hex 416172647661726b; asc Aardvark;; 1: len 6; hex 00000000a8f9; asc       ;; 2: len 7; hex 82000000e20110; asc        ;; 3: len 4; hex 8000000a; asc     ;;RECORD LOCKS space id 28 page no 4 n bits 72 index PRIMARY of table `test`.`Birds` trx id 43261 lock_mode X locks rec but not gap waitingRecord lock, heap no 2 PHYSICAL RECORD: n_fields 4; compact format; info bits 0 0: len 7; hex 42757a7a617264; asc Buzzard;; 1: len 6; hex 00000000a8fb; asc       ;; 2: len 7; hex 82000000e40110; asc        ;; 3: len 4; hex 80000014; asc     ;;