mysql加鎖分析
阿新 • • 發佈：2018-12-14
- 分析場景
1.1 工具：mysql5.5.53，在windows開啟兩個mysql命令列，m1、m2、m3，m1執行更新、刪除操作，m2查詢，m3查詢事務
1.2 表結構：兩個欄位，一個id，一個price
1.3 刪除SQL：delete from t1 where id=x limit 1
1.4 隔離級別# 設定m1、m2隔離級別為RC set session tx_isolation='read-committed'; # 檢視m1、m2隔離級別是否設定成功 select @@session.tx_isolation; - 分析開始
2.1
2.2# 建立t1表，id是主鍵，price是唯一鍵，使用innodb引擎 create table t1(id int(20) not null auto_increment,price int(10) not null,primary key(id),unique key(price))engine=innodb default charset=utf8mb4 collate=utf8mb4_general_ci; # m1插入1條資料 insert into t1(id,price) values(8,88888); # m1、m2查詢結果 select * from t1; +----+-------+ | id | price | +----+-------+ | 8 | 88888 | +----+-------+ # m1開啟事務，執行刪除 begin; delete from t1 where id=8 limit 1; # m3查詢事務 ① select * from information_schema.innodb_trx\G; ② show engine innodb status\G; ------------ TRANSACTIONS ------------ Trx id counter 258C35 Purge done for trx's n:o < 258C33 undo n:o < 0 History list length 766 LIST OF TRANSACTIONS FOR EACH SESSION: ---TRANSACTION 0, not started # m3事務未開啟 MySQL thread id 3, OS thread handle 0x9ec0, query id 637 localhost 127.0.0.1 root show engine innodb status ---TRANSACTION 258C31, not started # m2事務未開啟 MySQL thread id 2, OS thread handle 0x9f84, query id 631 localhost 127.0.0.1 root ---TRANSACTION 258C34, ACTIVE 29 sec # m1事務開啟，已持續29秒 2 lock struct(s), heap size 320, 1 row lock(s), undo log entries 1 # 2個鎖結構體，堆區佔用320KB，1個X鎖，1個回滾記錄 MySQL thread id 1, OS thread handle 0xa2d0, query id 636 localhost 127.0.0.1 root -------- # m1查詢（當前讀） select * from t1; empty set; # m2查詢有資料，m1提交後，m2就查詢不到資料（幻讀） select * from t1; +----+-------+ | id | price | +----+-------+ | 8 | 88888 | +----+-------+
2.3# 建立t2表，id是唯一鍵，price是主鍵，使用innodb引擎 create table t2(id int(20) not null ,price int(10) not null,primary key(price),unique key(id))engine=innodb default charset=utf8mb4 collate=utf8mb4_general_ci; # m1插入1條資料 insert into t2(id,price) values(1,10); # m1開啟事務，執行刪除 begin; delete from t2 where id=1; # m3查詢事務 ① select * from information_schema.innodb_trx\G; *************************** 1. row *************************** trx_id: 258C49 trx_state: RUNNING trx_started: 2018-10-10 16:49:46 trx_requested_lock_id: NULL trx_wait_started: NULL trx_weight: 4 trx_mysql_thread_id: 2 trx_query: NULL trx_operation_state: NULL trx_tables_in_use: 0 trx_tables_locked: 0 trx_lock_structs: 3 trx_lock_memory_bytes: 320 trx_rows_locked: 2 # 兩個行鎖，一個二級索引的X鎖，一個主鍵的X鎖 trx_rows_modified: 1 trx_concurrency_tickets: 0 trx_isolation_level: READ COMMITTED trx_unique_checks: 1 trx_foreign_key_checks: 1 trx_last_foreign_key_error: NULL trx_adaptive_hash_latched: 0 trx_adaptive_hash_timeout: 10000 1 rows in set (0.00 sec)
2.4# 建立t3表，id是普通索引，price是主鍵，使用innodb引擎 create table t3(id int(20) not null ,price int(10) not null,primary key(price),key(id))engine=innodb default charset=utf8mb4 collate=utf8mb4_general_ci; # m1插入4條資料 insert into t3(id,price) values(1,10),(1,20),(1,30),(1,40); # m1開啟事務，執行刪除 begin; delete from t3 where id=1; # m3查詢事務 ① select * from information_schema.innodb_trx\G; *************************** 1. row *************************** trx_id: 258C59 trx_state: RUNNING trx_started: 2018-10-10 17:11:31 trx_requested_lock_id: NULL trx_wait_started: NULL trx_weight: 6 trx_mysql_thread_id: 2 trx_query: NULL trx_operation_state: NULL trx_tables_in_use: 0 trx_tables_locked: 0 trx_lock_structs: 2 trx_lock_memory_bytes: 320 trx_rows_locked: 4 # 4行被鎖定，實際應該有8個，4個普通索引X鎖，4個主鍵X鎖 trx_rows_modified: 4 trx_concurrency_tickets: 0 trx_isolation_level: READ COMMITTED trx_unique_checks: 1 trx_foreign_key_checks: 1 trx_last_foreign_key_error: NULL trx_adaptive_hash_latched: 0 trx_adaptive_hash_timeout: 10000 1 row in set (0.00 sec)
2.5 在RR隔離級別下，2.1、2.2加鎖情況相同，2.3、2.4會加上間隙鎖，鎖預設不會提前釋放# 建立t4表，id無索引，price是主鍵，使用innodb引擎 create table t4(id int(20) not null ,price int(10) not null,primary key(price))engine=innodb default charset=utf8mb4 collate=utf8mb4_general_ci; # m1插入5條資料 insert into t4(id,price) values(1,10),(1,20),(1,30),(1,40),(2,50); # m1開啟事務，執行刪除 begin; delete from t4 where id=1; # m3查詢事務 ① select * from information_schema.innodb_trx\G; ② 查詢事務id：SELECT TRX_ID FROM INFORMATION_SCHEMA.INNODB_TRX WHERE TRX_MYSQL_THREAD_ID = CONNECTION_ID(); *************************** 1. row *************************** trx_id: 258C61 trx_state: RUNNING trx_started: 2018-10-10 17:21:22 trx_requested_lock_id: NULL trx_wait_started: NULL trx_weight: 6 trx_mysql_thread_id: 2 trx_query: NULL trx_operation_state: NULL trx_tables_in_use: 0 trx_tables_locked: 0 trx_lock_structs: 2 trx_lock_memory_bytes: 320 trx_rows_locked: 4 # 4個行鎖，實際上是5個行鎖，mysql資料引擎層會對所有行加X鎖，mysql服務層會對不符合條件的解鎖（使用了semi-consistent read） trx_rows_modified: 4 trx_concurrency_tickets: 0 trx_isolation_level: READ COMMITTED trx_unique_checks: 1 trx_foreign_key_checks: 1 trx_last_foreign_key_error: NULL trx_adaptive_hash_latched: 0 trx_adaptive_hash_timeout: 10000 1 row in set (0.00 sec)
2.6 死鎖執行sql順序（id為主鍵）： m1：delete from t1 where id=14; m2：delete from t1 where id=13; m1：delete from t1 where id=13; m2：delete from t1 where id=14; ------------------------ LATEST DETECTED DEADLOCK ------------------------ 181011 10:21:21 *** (1) TRANSACTION: TRANSACTION 258CB6, ACTIVE 68 sec starting index read mysql tables in use 1, locked 1 LOCK WAIT 3 lock struct(s), heap size 320, 2 row lock(s), undo log entries 1 MySQL thread id 2, OS thread handle 0xa2d0, query id 985 localhost 127.0.0.1 root updating delete from t1 where id=13 *** (1) WAITING FOR THIS LOCK TO BE GRANTED: RECORD LOCKS space id 0 page no 163855 n bits 72 index `PRIMARY` of table `trx`.`t1` trx id 258CB6 lock_mode X locks rec but not gap waiting Record lock, heap no 2 PHYSICAL RECORD: n_fields 4; compact format; info bits 32 0: len 4; hex 8000000d; asc ;; 1: len 6; hex 000000258cb4; asc % ;; 2: len 7; hex 1b000380022cea; asc , ;; 3: len 4; hex 80000309; asc ;; *** (2) TRANSACTION: TRANSACTION 258CB4, ACTIVE 154 sec starting index read, thread declared inside InnoDB 500 mysql tables in use 1, locked 1 3 lock struct(s), heap size 320, 2 row lock(s), undo log entries 1 MySQL thread id 3, OS thread handle 0x9f84, query id 986 localhost 127.0.0.1 root updating delete from t1 where id=14 *** (2) HOLDS THE LOCK(S): RECORD LOCKS space id 0 page no 163855 n bits 72 index `PRIMARY` of table `trx`.`t1` trx id 258CB4 lock_mode X locks rec but not gap Record lock, heap no 2 PHYSICAL RECORD: n_fields 4; compact format; info bits 32 0: len 4; hex 8000000d; asc ;; 1: len 6; hex 000000258cb4; asc % ;; 2: len 7; hex 1b000380022cea; asc , ;; 3: len 4; hex 80000309; asc ;; *** (2) WAITING FOR THIS LOCK TO BE GRANTED: RECORD LOCKS space id 0 page no 163855 n bits 72 index `PRIMARY` of table `trx`.`t1` trx id 258CB4 lock_mode X locks rec but not gap waiting Record lock, heap no 4 PHYSICAL RECORD: n_fields 4; compact format; info bits 32 0: len 4; hex 8000000e; asc ;; 1: len 6; hex 000000258cb6; asc % ;; 2: len 7; hex 1c000380132b35; asc +5;; 3: len 4; hex 8000029a; asc ;; *** WE ROLL BACK TRANSACTION (2)