[ 傳送門：MySQL鎖：01.總覽 ](https://www.cnblogs.com/konggg/p/14133916.html) [ 傳送門：MySQL鎖：02.InnoDB鎖 ](https://www.cnblogs.com/konggg/p/14134036.html) [ 傳送門：MySQL鎖：03.InnoDB行鎖 ](https://www.cnblogs.com/konggg/p/14134114.html) [TOC] 通過索引實現行鎖，在索引記錄上加鎖。 沒有索引就無法實現行鎖，升級成全表記錄鎖，等同於表鎖。 理解InnoDB獨特的行鎖執行機制，認識特有的四種行鎖粒度——lock_ordinary、lock_gap、lock_rec_not_gap、lock_insert_intention  # InnoDB 行鎖 - 預設都是加lock_ordinary鎖 - 如果是唯一索引列上的等值查詢，則退化成lock_rec_not_gap - 所有版本，非唯一索引列上的範圍查詢，遇到第一個不符合條件的記錄也會加上lock_ordinary。 - 8.0.18版本以前，主要指<=場景：唯一索引列上的範圍查詢，遇到第一個不符合條件的記錄也會加上lock_ordinary ，在RC下會釋放，RR下不會釋放。 - 8.0.18版本以前，非唯一索引列上的等值查詢，向右遍歷遇到第一個不符合條件的記錄時，先加上lock_ordinary，再退化成lock_gap。 ## 鎖排查可以用的檢視和資料字典 ``` mysql> show engine innodb status \G mysql> select * from performance_schema.data_lock_waits; mysql> select * from performance_schema.data_locks; mysql> select * from performance_schema.metadata_locks; ``` ## InnoDB 行鎖相容性 | | | 請求的鎖型別 | 請求的鎖型別 | 請求的鎖型別 | 請求的鎖型別 | | -------------- | --------------------- | ------------- | ---------------- | ------------ | --------------------- | | | | lock_ordinary | lock_rec_not_gap | lock_gap | lock_insert_intention | | 已獲得的鎖型別 | lock_ordinary | X | X | O | X | | 已獲得的鎖型別 | lock_rec_not_gap | X | X | O | O | | 已獲得的鎖型別 | lock_gap | O | O | O | X | | 已獲得的鎖型別 | lock_insert_intention | O | O | O | O | - gap只和insert intention鎖衝突 - insert intention和任何鎖都不衝突，除非也在相同位置做意向插入鎖 - 先獲得意向插入鎖的，再嘗試上gap lock是可以的 - 但是反過來 ，先獲得gap lock的，再嘗試加上意向插入鎖便會阻塞， - 原因是：先獲得意向插入鎖時，實際上插入已經成功，意向插入鎖會被轉變為對具體記錄的ordinary 或 rec_not_gap ，此時二者都與lock gap相容。 # InnoDB行鎖之共享鎖 ### 共享鎖： - 不允許其他事務修改被鎖定的行，只能讀 - select .. for share/ lock in share mode - 自動提交模式下的普通select是一致性非鎖定讀，不加鎖。 自動提交模式下， 不使用begin開啟事務，直接select的話： select * from xxx where .. 不加鎖 select * from xxx where .. for share ，也查詢不到加鎖， 但是實際上是加鎖的，只不過鎖的時間及其的短暫。 驗證：  此時，用排他鎖來驗證自動提交模式的for share究竟是否產生鎖動作。  可以看出，自動提交模式下select（不加for share）是一致性非鎖定讀，但是加for share後，是會有鎖定動作的，只不過沒有阻塞的情況下，鎖的持續時間是非常短暫的。 # 檢視InnoDB鎖 - 開啟引數：innodb_status_output_locks=1; 以支援使用 show engine innodb status 檢視鎖詳情。 ``` mysql> begin ; select * from k1 where id=4 for update; Query OK, 0 rows affected (0.00 sec) mysql> show engine innodb status \G .. MySQL thread id 31, OS thread handle 139620328457984, query id 1297 localhost root **TABLE LOCK table `kk`.`k1` trx id 1901 lock mode IX** RECORD LOCKS space id 3 page no 10 n bits 1056 index id of table `kk`.`k1` trx id 1901 lock_mode X Record lock, heap no 3 PHYSICAL RECORD: n_fields 2; compact format; info bits 0 0: len 4; hex 80000004; asc ;; 1: len 6; hex 000000000902; asc ;; RECORD LOCKS space id 3 page no 9 n bits 320 index GEN_CLUST_INDEX of table `kk`.`k1` trx id 1901 lock_mode X locks rec but not gap Record lock, heap no 248 PHYSICAL RECORD: n_fields 6; compact format; info bits 0 0: len 6; hex 000000000902; asc ;; 1: len 6; hex 000000000663; asc c;; 2: len 7; hex 82000000940110; asc ;; 3: len 4; hex 80000004; asc ;; 4: SQL NULL; 5: SQL NULL; RECORD LOCKS space id 3 page no 10 n bits 1056 index id of table `kk`.`k1` trx id 1901 lock_mode X locks gap before rec Record lock, heap no 4 PHYSICAL RECORD: n_fields 2; compact format; info bits 0 0: len 4; hex 80000016; asc ;; 1: len 6; hex 000000000200; asc ;; .. - space id 3 表的表空間ID - page no 10 鎖所在datapage的ID - heap no 4，slot no，記錄在page物理上的第幾個位置。 ``` - 也可以查詢P_S表 ``` mysql> select * from performance_schema.data_locks; +--------+----------------------------------------+-----------------------+-----------+----------+---------------+-------------+----------------+-------------------+------------+-----------------------+-----------+---------------+-------------+-----------+ | ENGINE | ENGINE_LOCK_ID | ENGINE_TRANSACTION_ID | THREAD_ID | EVENT_ID | OBJECT_SCHEMA | OBJECT_NAME | PARTITION_NAME | SUBPARTITION_NAME | INDEX_NAME | OBJECT_INSTANCE_BEGIN | LOCK_TYPE | LOCK_MODE | LOCK_STATUS | LOCK_DATA | +--------+----------------------------------------+-----------------------+-----------+----------+---------------+-------------+----------------+-------------------+------------+-----------------------+-----------+---------------+-------------+-----------+ | INNODB | 139620969519720:1072:139620864029240 | 2211 | 85 | 79 | kk | k1 | NULL | NULL | NULL | 139620864029240 | TABLE | IX | GRANTED | NULL | | INNODB | 139620969519720:15:4:5:139620864026200 | 2211 | 85 | 79 | kk | k1 | NULL | NULL | PRIMARY | 139620864026200 | RECORD | X,REC_NOT_GAP | GRANTED | 4 | +--------+----------------------------------------+-----------------------+-----------+----------+---------------+-------------+----------------+-------------------+------------+-----------------------+-----------+---------------+-------------+-----------+ 2 rows in set (0.00 sec) ``` - 再看下IS鎖的情況 ``` mysql> begin ; select * from k1 where id=4 for share; Query OK, 0 rows affected (0.00 sec) mysql> show engine innodb status \G 看不到IS鎖資訊。 1 row in set (0.00 sec) mysql> select * from performance_schema.data_locks; +--------+----------------------------------------+-----------------------+-----------+----------+---------------+-------------+----------------+-------------------+------------+-----------------------+-----------+---------------+-------------+-----------+ | ENGINE | ENGINE_LOCK_ID | ENGINE_TRANSACTION_ID | THREAD_ID | EVENT_ID | OBJECT_SCHEMA | OBJECT_NAME | PARTITION_NAME | SUBPARTITION_NAME | INDEX_NAME | OBJECT_INSTANCE_BEGIN | LOCK_TYPE | LOCK_MODE | LOCK_STATUS | LOCK_DATA | +--------+----------------------------------------+-----------------------+-----------+----------+---------------+-------------+----------------+-------------------+------------+-----------------------+-----------+---------------+-------------+-----------+ | INNODB | 139620969519720:1072:139620864029240 | 421095946230376 | 85 | 83 | kk | k1 | NULL | NULL | NULL | 139620864029240 | TABLE | IS | GRANTED | NULL | | INNODB | 139620969519720:15:4:5:139620864026200 | 421095946230376 | 85 | 83 | kk | k1 | NULL | NULL | PRIMARY | 139620864026200 | RECORD | S,REC_NOT_GAP | GRANTED | 4 | +--------+----------------------------------------+-----------------------+-----------+----------+---------------+-------------+----------------+-------------------+------------+-----------------------+-----------+---------------+-------------+-----------+ 2 rows in set (0.00 sec) ``` 驗證一下IS和IX的相容 ``` t1: mysql> begin ; select * from k1 where id=4 for share; Query OK, 0 rows affected (0.00 sec) +------+------+------+ | id | dtl | name | +------+------+------+ | 4 | NULL | NULL | +------+------+------+ 1 row in set (0.00 sec) t2: mysql> begin ; select * from k1 where id=11 for update; Query OK, 0 rows affected (0.00 sec) Empty set (0.00 sec) --注意:加鎖加不在相同行，否則hang。 t3: mysql> select * from performance_schema.data_locks; +--------+----------------------------------------+-----------------------+-----------+----------+---------------+-------------+----------------+-------------------+------------+-----------------------+-----------+---------------+-------------+------------------------+ | ENGINE | ENGINE_LOCK_ID | ENGINE_TRANSACTION_ID | THREAD_ID | EVENT_ID | OBJECT_SCHEMA | OBJECT_NAME | PARTITION_NAME | SUBPARTITION_NAME | INDEX_NAME | OBJECT_INSTANCE_BEGIN | LOCK_TYPE | LOCK_MODE | LOCK_STATUS | LOCK_DATA | +--------+----------------------------------------+-----------------------+-----------+----------+---------------+-------------+----------------+-------------------+------------+-----------------------+-----------+---------------+-------------+------------------------+ | INNODB | 139620969519720:1072:139620864029240 | 2212 | 85 | 89 | kk | k1 | NULL | NULL | NULL | 139620864029240 | TABLE | IX | GRANTED | NULL | | INNODB | 139620969519720:15:4:1:139620864026200 | 2212 | 85 | 89 | kk | k1 | NULL | NULL | PRIMARY | 139620864026200 | RECORD | X | GRANTED | supremum pseudo-record | | INNODB | 139620969521464:1072:139620864041176 | 421095946232120 | 84 | 110 | kk | k1 | NULL | NULL | NULL | 139620864041176 | TABLE | IS | GRANTED | NULL | | INNODB | 139620969521464:15:4:5:139620864038296 | 421095946232120 | 84 | 110 | kk | k1 | NULL | NULL | PRIMARY | 139620864038296 | RECORD | S,REC_NOT_GAP | GRANTED | 4 | +--------+----------------------------------------+-----------------------+-----------+----------+---------------+-------------+----------------+-------------------+------------+-----------------------+-----------+---------------+-------------+------------------------+ 4 rows in set (0.00 sec) ``` ## InnoDB行鎖實現機制 - 基於索引實現，逐行檢查，逐行加鎖 - 沒有索引的列上需要加鎖時，會先對所有記錄加鎖，再根據實際情況決定是否釋放鎖。 - 輔助索引上加鎖時，同時要回溯到主鍵索引上再加一次鎖。 - 加鎖的基本單位預設時lock_ordinary，當索引就具有唯一性的時候退化為lock_rec_not_gap - 等值條件逐行加鎖時，會向右遍歷到第一個不滿足條件的記錄，然後lock_ordinary退化為lock_gap - 如果發生唯一性檢測（insert\update動作），那麼會發生lock_ordinary ， 再退化成lock_rec_not_gap - 唯一索引的範圍條件加鎖時，也會對第一個不滿足條件的記錄加鎖 ### 對普通索引上鎖 普通索引next-key lock + 主鍵 not gap + 普通索引的下一個記錄的gap lock（見示意圖）。 ``` mysql> select * from k2; +----+------+------+ | id | dtl | un | +----+------+------+ | 1 | 1 | 1 | | 2 | 2 | 2 | | 3 | 5 | 5 | (回溯到pk上鎖) ------------------------------------------ <- gap (同時鎖住普通索引下一個記錄前的gap) | 4 | 7 | 7 |* | 5 | 11 | 11 | +----+------+------+ 5 rows in set (0.00 sec) ``` - 輔助索引上鎖的驗證實驗 ``` mysql> show create table k2\G *************************** 1. row *************************** Table: k2 Create Table: CREATE TABLE `k2` ( `id` int NOT NULL AUTO_INCREMENT, `dtl` int DEFAULT NULL, `un` int DEFAULT NULL, PRIMARY KEY (`id`), UNIQUE KEY `dtl` (`dtl`), KEY `un` (`un`) ) ENGINE=InnoDB AUTO_INCREMENT=9 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci 1 row in set (0.00 sec) mysql> select * from k2; +----+------+------+ | id | dtl | un | +----+------+------+ | 1 | 1 | 1 | | 2 | 2 | 2 | | 3 | 5 | 5 | | 4 | 7 | 7 |* | 5 | 11 | 11 | +----+------+------+ 5 rows in set (0.00 sec) mysql> begin ; select * from k2 where un=5 for update; Query OK, 0 rows affected (0.00 sec) +----+------+------+ | id | dtl | un | +----+------+------+ | 3 | 5 | 5 | +----+------+------+ 1 row in set (0.00 sec) mysql> select * from performance_schema.data_locks\G *************************** 1. row *************************** ENGINE: INNODB ENGINE_LOCK_ID: 139620969521464:1061:139620864041176 ENGINE_TRANSACTION_ID: 1944 THREAD_ID: 70 EVENT_ID: 65 OBJECT_SCHEMA: kk OBJECT_NAME: k2 PARTITION_NAME: NULL SUBPARTITION_NAME: NULL INDEX_NAME: NULL OBJECT_INSTANCE_BEGIN: 139620864041176 LOCK_TYPE: TABLE* LOCK_MODE: IX* LOCK_STATUS: GRANTED LOCK_DATA: NULL *************************** 2. row *************************** ENGINE: INNODB ENGINE_LOCK_ID: 139620969521464:4:6:9:139620864038296 ENGINE_TRANSACTION_ID: 1944 THREAD_ID: 70 EVENT_ID: 65 OBJECT_SCHEMA: kk OBJECT_NAME: k2 PARTITION_NAME: NULL SUBPARTITION_NAME: NULL INDEX_NAME: un* OBJECT_INSTANCE_BEGIN: 139620864038296 LOCK_TYPE: RECORD （nextkey-lock）* LOCK_MODE: X LOCK_STATUS: GRANTED LOCK_DATA: 5, 3 （un key value, primary key value, index Condion特性）* *************************** 3. row *************************** ENGINE: INNODB ENGINE_LOCK_ID: 139620969521464:4:4:11:139620864038640 ENGINE_TRANSACTION_ID: 1944 THREAD_ID: 70 EVENT_ID: 65 OBJECT_SCHEMA: kk OBJECT_NAME: k2 PARTITION_NAME: NULL SUBPARTITION_NAME: NULL INDEX_NAME: PRIMARY* OBJECT_INSTANCE_BEGIN: 139620864038640 LOCK_TYPE: RECORD LOCK_MODE: X,REC_NOT_GAP* LOCK_STATUS: GRANTED LOCK_DATA: 3* *************************** 4. row *************************** ENGINE: INNODB ENGINE_LOCK_ID: 139620969521464:4:6:10:139620864038984 ENGINE_TRANSACTION_ID: 1944 THREAD_ID: 70 EVENT_ID: 65 OBJECT_SCHEMA: kk OBJECT_NAME: k2 PARTITION_NAME: NULL SUBPARTITION_NAME: NULL INDEX_NAME: un* OBJECT_INSTANCE_BEGIN: 139620864038984 LOCK_TYPE: RECORD LOCK_MODE: X,GAP* 確認下一個記錄不符合條件，回退nextkey-lock 為 lock-gap. LOCK_STATUS: GRANTED LOCK_DATA: 7, 4 （un key value, primary key value, index Condion特性）* 4 rows in set (0.00 sec) ``` ## InnoDB隱式、顯式鎖 - 顯式鎖(explicit-lock) - select .. from .. where .. for update / for share - 隱式鎖(implicit-lock) - update set .. where .. - 任何輔助索引上鎖，或非索引列上鎖，都要回溯到主鍵上再加鎖。 - 和其他session有衝突時，隱式鎖轉換為顯式鎖。（沒實驗驗證出來。） 如果發生唯一性檢測（insert\update動作），那麼會發生lock_ordinary ， 再退化成lock_rec