正常情況下，死鎖發生時，權重最小的連接將被kill并回滾。但是為了找出語句來優化，啟用可啟用死鎖將死鎖信息記錄下來。
#step 1：窗口一
mysql> start transaction;
mysql> update aa set name='aaa' where id = 1;
#step 2：窗口二
mysql> start transaction;
mysql> update bb set name='bbb' where id = 1;
#step 3：窗口一
mysql> update bb set name='bbb';
#step 4：窗口三
#是否自動提交
mysql> show variables like 'autocommit';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| autocommit | ON |
+---------------+-------+
#查看當前連接
mysql> show processlist;
mysql> show full processlist;
mysql> SELECT * FROM INFORMATION_SCHEMA.PROCESSLIST;
+----+------+-----------+------+---------+------+-------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------+------+---------+------+-------+------------------+
| 4 | root | localhost | test | Sleep | 244 | | NULL |
| 5 | root | localhost | test | Sleep | 111 | | NULL |
| 6 | root | localhost | NULL | Query | 0 | init | show processlist |
+----+------+-----------+------+---------+------+-------+------------------+
#查看當前正在被鎖的事務（鎖請求超時后則查不到）
mysql> SELECT * FROM INFORMATION_SCHEMA.INNODB_LOCKS;
+------------------+-------------+-----------+-----------+-------------+-----------------+------------+-----------+----------+----------------+
| lock_id | lock_trx_id | lock_mode | lock_type | lock_table | lock_index | lock_space | lock_page | lock_rec | lock_data |
+------------------+-------------+-----------+-----------+-------------+-----------------+------------+-----------+----------+----------------+
| 130718495:65:3:4 | 130718495 | X | RECORD | `test`.`bb` | GEN_CLUST_INDEX | 65 | 3 | 4 | 0x000000000300 |
| 130718496:65:3:4 | 130718496 | X | RECORD | `test`.`bb` | GEN_CLUST_INDEX | 65 | 3 | 4 | 0x000000000300 |
+------------------+-------------+-----------+-----------+-------------+-----------------+------------+-----------+----------+----------------+
#查看當前等待鎖的事務（鎖請求超時后則查不到）
mysql> SELECT * FROM INFORMATION_SCHEMA.INNODB_LOCK_WAITS;
+-------------------+-------------------+-----------------+------------------+
| requesting_trx_id | requested_lock_id | blocking_trx_id | blocking_lock_id |
+-------------------+-------------------+-----------------+------------------+
| 130718499 | 130718499:65:3:4 | 130718500 | 130718500:65:3:4 |
+-------------------+-------------------+-----------------+------------------+
#查看當前未提交的事務（如果死鎖等待超時,事務可能還沒有關閉）
mysql> SELECT * FROM INFORMATION_SCHEMA.INNODB_TRX;
+--------------------------------------------------------------------------------------------------------+
| trx_id | trx_state | trx_started | trx_requested_lock_id | trx_wait_started | trx_weight |
+-----------+-----------+---------------------+-----------------------+---------------------+------------+
| 130718500 | RUNNING | 2018-03-12 09:28:10 | NULL | NULL | 3 |
| 130718499 | LOCK WAIT | 2018-03-12 09:27:59 | 130718499:65:3:4 | 2018-03-12 09:32:48 | 5 |
==========================================================================================================
| trx_mysql_thread_id | trx_query | trx_operation_state | trx_tables_in_use |
+---------------------+---------------------------------------+---------------------+-------------------+
| 4 | NULL | NULL | 0 |
| 5 | update bb set name='bbb' | starting index read | 1 |
=========================================================================================================
| trx_tables_locked | trx_lock_structs | trx_lock_memory_bytes | trx_rows_locked | trx_rows_modified |
+-------------------+------------------+-----------------------+-----------------+-------------------+
| 0 | 2 | 360 | 3 | 1 |
| 1 | 4 | 1184 | 4 | 1 |
===========================================================================================================================
| trx_concurrency_tickets | trx_isolation_level | trx_unique_checks | trx_foreign_key_checks | trx_last_foreign_key_error |
+-------------------------+---------------------+-------------------+------------------------+----------------------------+
| 0 | REPEATABLE READ | 1 | 1 | NULL |
| 0 | REPEATABLE READ | 1 | 1 | NULL |
===========================================================================================================================
| trx_adaptive_hash_latched | trx_adaptive_hash_timeout | trx_is_read_only | trx_autocommit_non_locking |
+---------------------------+---------------------------+------------------+----------------------------+
| 0 | 10000 | 0 | 0 |
| 0 | 10000 | 0 | 0 |
+---------------------------+---------------------------+------------------+----------------------------+
#查看正在被訪問的表
mysql> show OPEN TABLES where In_use > 0;
+----------+-------+--------+-------------+
| Database | Table | In_use | Name_locked |
+----------+-------+--------+-------------+
| test | bb | 1 | 0 |
+----------+-------+--------+-------------+
#step 3：窗口一 （若第三步中鎖請求太久，則出現鎖超時而終止執行）
mysql> update bb set name='bbb';
ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction
#"窗口一" 鎖請求超時前，執行第五步，使死鎖產生，則該連接 "窗口二" 執行終止，"窗口一" 順利執行
#step 5：窗口二
mysql> update aa set name='aa';
ERROR 1213 (40001): Deadlock found when trying to get lock; try restarting transaction
查看最近一個死鎖情況
#查看最近一個死鎖情況
mysql> SHOW ENGINE INNODB STATUS\G ;
...............
------------------------
LATEST DETECTED DEADLOCK
------------------------
2018-03-12 11:01:06 7ffb4993a700 #發生時間
*** (1) TRANSACTION: #事務1
TRANSACTION 130718515, ACTIVE 19 sec starting index read
mysql tables in use 1, locked 1 #正被訪問的表
LOCK WAIT 4 lock struct(s), heap size 1184, 4 row lock(s), undo log entries 1 #影響行數
MySQL thread id 5, OS thread handle 0x7ffb498f8700, query id 205 localhost root updating #線程/連接host/用戶
update bb set name='bb' #請求語句
*** (1) WAITING FOR THIS LOCK TO BE GRANTED: #等待以下資源 （鎖定位置及鎖模式）
RECORD LOCKS space id 65 page no 3 n bits 72 index `GEN_CLUST_INDEX` of table `test`.`bb` trx id 130718515 lock_mode X waiting
Record lock, heap no 5 PHYSICAL RECORD: n_fields 5; compact format; info bits 0
0: len 6; hex 000000000300; asc ;;
1: len 6; hex 000007ca9b34; asc 4;;
2: len 7; hex 1f000002092075; asc u;;
3: len 4; hex 80000001; asc ;;
4: len 2; hex 6262; asc bb;;
*** (2) TRANSACTION: #事務2
TRANSACTION 130718516, ACTIVE 14 sec starting index read
mysql tables in use 1, locked 1
4 lock struct(s), heap size 1184, 4 row lock(s), undo log entries 1
MySQL thread id 4, OS thread handle 0x7ffb4993a700, query id 206 localhost root updating
update aa set name='aa' #請求語句
*** (2) HOLDS THE LOCK(S): #持有鎖資源
RECORD LOCKS space id 65 page no 3 n bits 72 index `GEN_CLUST_INDEX` of table `test`.`bb` trx id 130718516 lock_mode X
Record lock, heap no 1 PHYSICAL RECORD: n_fields 1; compact format; info bits 0
0: len 8; hex 73757072656d756d; asc supremum;;
Record lock, heap no 3 PHYSICAL RECORD: n_fields 5; compact format; info bits 0
0: len 6; hex 000000000301; asc ;;
1: len 6; hex 000007ca9b17; asc ;;
2: len 7; hex 9000000144011e; asc D ;;
3: len 4; hex 80000002; asc ;;
4: len 2; hex 6262; asc bb;;
Record lock, heap no 5 PHYSICAL RECORD: n_fields 5; compact format; info bits 0
0: len 6; hex 000000000300; asc ;;
1: len 6; hex 000007ca9b34; asc 4;;
2: len 7; hex 1f000002092075; asc u;;
3: len 4; hex 80000001; asc ;;
4: len 2; hex 6262; asc bb;;
*** (2) WAITING FOR THIS LOCK TO BE GRANTED:
RECORD LOCKS space id 64 page no 3 n bits 80 index `GEN_CLUST_INDEX` of table `test`.`aa` trx id 130718516 lock_mode X waiting
Record lock, heap no 7 PHYSICAL RECORD: n_fields 5; compact format; info bits 0
0: len 6; hex 000000000200; asc ;;
1: len 6; hex 000007ca9b33; asc 3;;
2: len 7; hex 1e000001d53057; asc 0W;;
3: len 4; hex 80000001; asc ;;
4: len 2; hex 6161; asc aa;;
*** WE ROLL BACK TRANSACTION (2)
...............
#死鎖記錄只記錄最近一個死鎖信息，若要將每個死鎖信息都保存到錯誤日志，啟用以下參數：
mysql> show variables like 'innodb_print_all_deadlocks';
+----------------------------+-------+
| Variable_name | Value |
+----------------------------+-------+
| innodb_print_all_deadlocks | OFF |
+----------------------------+-------+
#上面 【step 3：窗口一】若一直請求不到資源，默認50秒則出現鎖等待超時。
mysql> show variables like 'innodb_lock_wait_timeout';
+--------------------------+-------+
| Variable_name | Value |
+--------------------------+-------+
| innodb_lock_wait_timeout | 50 |
+--------------------------+-------+
ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction
#設置全局變量 鎖等待超時為60秒（新的連接生效）
#mysql> set session innodb_lock_wait_timeout=50;
mysql> set global innodb_lock_wait_timeout=60;
#上面測試中，當事務中的某個語句超時只回滾該語句，事務的完整性屬于被破壞了。為了回滾這個事務，啟用以下參數：
mysql> show variables like 'innodb_rollback_on_timeout';
+----------------------------+-------+
| Variable_name | Value |
+----------------------------+-------+
| innodb_rollback_on_timeout | OFF |
+----------------------------+-------+
最終參數設置如下：(重啟服務重新連接測試)
[mysqld]
log-error =/var/log/mysqld3306.log
innodb_lock_wait_timeout=60 #鎖請求超時時間(秒)
innodb_rollback_on_timeout = 1 #事務中某個語句鎖請求超時將回滾真個事務
innodb_print_all_deadlocks = 1 #死鎖都保存到錯誤日志
#若手動刪除堵塞會話，刪除 Command='Sleep' 、無State、無Info、trx_weight 權重最小的。
show processlist;
SELECT trx_mysql_thread_id,trx_state,trx_started,trx_weight FROM INFORMATION_SCHEMA.INNODB_TRX;
總結
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