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Mysql InnoDB的鎖定機制實例詳解

1.InnoDB的鎖定機制

InnoDB存儲引擎支持行級鎖，支持事務(wù)處理，事務(wù)是有一組SQL語句組成的邏輯處理單元，他的ACID特性如下：

原子性(Atomicity): 事務(wù)具有原子不可分割的特性，要么一起執(zhí)行，要么都不執(zhí)行。
一致性(Consistency): 在事務(wù)開始和事務(wù)結(jié)束時，數(shù)據(jù)都保持一致狀態(tài)。
隔離性(Isolation): 在事務(wù)開始和結(jié)束過程中，事務(wù)保持著一定的隔離特性，保證事務(wù)不受外部并發(fā)數(shù)據(jù)操作的影響。
持久性(Durability): 在事務(wù)完成后，數(shù)據(jù)將會被持久化到數(shù)據(jù)庫中。

并發(fā)事務(wù)能提高數(shù)據(jù)庫資源的利用率，提高了數(shù)據(jù)庫的事務(wù)吞吐量，但并發(fā)事務(wù)也存在一些問題，主要包括：

更新丟失(Lost Update): 兩個事務(wù)更新同一條數(shù)據(jù)，但第二個事務(wù)中途失敗退出，導(dǎo)致兩個修改都失效了；因為此時數(shù)據(jù)庫沒有執(zhí)行任何鎖操作，并發(fā)事務(wù)并沒有被隔離。(現(xiàn)代數(shù)據(jù)庫已經(jīng)不存在這種問題)
臟讀(Dirty Reads): 一個事務(wù)讀了某行數(shù)據(jù)，但是另一個事務(wù)已經(jīng)更新了這行數(shù)據(jù)，這是非常危險的，很可能導(dǎo)致所有的操作被回滾。
不可重復(fù)讀: 一個事務(wù)對一行數(shù)據(jù)重復(fù)讀取兩次(多次)，可是得到了不同的結(jié)果,在兩次讀取過程中，有可能存在另一個事務(wù)對數(shù)據(jù)進行了修改。
幻讀:事務(wù)在操作過程中進行兩次查詢，第二次查詢結(jié)果包含了第一次沒有出現(xiàn)的數(shù)據(jù)。出現(xiàn)幻讀的主要原因是兩次查詢過程中另一個事務(wù)插入新的數(shù)據(jù)。

數(shù)據(jù)庫并發(fā)中的“更新丟失”通常應(yīng)該是完全避免的，但防止更新丟失數(shù)據(jù)，并不能單靠數(shù)據(jù)庫事務(wù)控制來解決，需要應(yīng)用程序?qū)σ碌臄?shù)據(jù)加必要的鎖來解決，而以上出現(xiàn)的數(shù)據(jù)庫問題都必要由數(shù)據(jù)庫提供一定的事務(wù)隔離機制來解決。為了避免數(shù)據(jù)庫事務(wù)并發(fā)帶來的問題，在標(biāo)準(zhǔn)SQL規(guī)范中定義了4個事務(wù)的隔離級別，不同的隔離級別對事務(wù)處理不一樣。

數(shù)據(jù)庫隔離級別的比較

隔離級別	讀數(shù)據(jù)一致性	臟讀	不可重復(fù)讀	幻讀
未提交讀 (Read uncommitted)	最低級別，只能保證不讀取物理上損壞的數(shù)據(jù)	是	是	是
已提交讀 (Read committed)	語句級	否	是	是
可重復(fù)讀 (Repeatable read)	事務(wù)級	否	否	是
可序列化 (Serializable)	最高級別，事務(wù)級	否	否	否

InnoDB存儲引擎實現(xiàn)了4中行鎖，分別時共享鎖(S)、排他鎖(X)、意向共享鎖(IS)、意向排他鎖(IX)。

共享鎖：大家都能讀，但是不能改，只有其中一個獨占共享鎖時候才能改；
排它鎖：我要改，你們都不能改，也不能讀(但可以MVCC快照讀)

理解意向鎖

意向鎖不會和行級的S和X鎖沖突，只會和表級的S和X鎖沖突

意向鎖是為了避免遍歷全部行鎖

考慮這個例子：

事務(wù)A鎖住了表中的一行，讓這一行只能讀，不能寫。

之后，事務(wù)B申請整個表的寫鎖。

如果事務(wù)B申請成功，那么理論上它就能修改表中的任意一行，這與A持有的行鎖是沖突的。

數(shù)據(jù)庫需要避免這種沖突，就是說要讓B的申請被阻塞，直到A釋放了行鎖。

數(shù)據(jù)庫要怎么判斷這個沖突呢？

step1：判斷表是否已被其他事務(wù)用表鎖鎖表

step2：判斷表中的每一行是否已被行鎖鎖住。

注意step2，這樣的判斷方法效率實在不高，因為需要遍歷整個表。

于是就有了意向鎖。

在意向鎖存在的情況下，事務(wù)A必須先申請表的意向共享鎖，成功后再申請一行的行鎖。

在意向鎖存在的情況下，上面的判斷可以改成

step1：不變

step2：發(fā)現(xiàn)表上有意向共享鎖，說明表中有些行被共享行鎖鎖住了，因此，事務(wù)B申請表的寫鎖會被阻塞。

1.1通過索引檢索數(shù)據(jù)，上共享鎖，行鎖(如果不通過索引，會使用表鎖)

1.1通過索引檢索數(shù)據(jù)，上共享鎖，行鎖
SessionA                    SessionB
mysql> set autocommit=0;            mysql> set autocommit=0;
Query OK, 0 rows affected (0.02 sec)      Query OK, 0 rows affected (0.02 sec)
mysql> select * from test;           mysql> select * from test;
--------------------------------------------------------------------------------
+----+-------+-------+-------+         +----+-------+-------+-------+              
| id | name | money | level |         | id | name | money | level |
+----+-------+-------+-------+         +----+-------+-------+-------+
| 1 | tom  |  100 |   1 |         | 1 | tom  |  100 |   1 |
| 2 | jack |  200 |   2 |         | 2 | jack |  200 |   2 |
| 3 | lucas |  300 |   3 |         | 3 | lucas |  300 |   3 |
+----+-------+-------+-------+         +----+-------+-------+-------+
3 rows in set (0.00 sec)            3 rows in set (0.00 sec)
--------------------------------------------------------------------------------
對主鍵索引上共享鎖,其他事務(wù)也能獲取到共享鎖
mysql> select * from test where         
id=1 lock in share mode;
+----+------+-------+-------+
| id | name | money | level |
+----+------+-------+-------+
| 1 | tom |  100 |   1 |
+----+------+-------+-------+
1 row in set (0.01 sec)
--------------------------------------------------------------------------------
                        事務(wù)B也能繼續(xù)加共享鎖
                        mysql> select * from test where         
                        id=1 lock in share mode;
                        +----+------+-------+-------+
                        | id | name | money | level |
                        +----+------+-------+-------+
                        | 1 | tom |  100 |   1 |
                        +----+------+-------+-------+
                        1 row in set (0.01 sec)
                        但無法更新，因為事務(wù)A也加了共享鎖
                        mysql> update test set level=11 where id=1;
                        ERROR 1205 (HY000): Lock wait timeout exceeded;
                        try restarting transaction
                        
                        MORE:
                        無法加排它鎖
                        select *from test where id=1 for update;
                        ERROR 1205 (HY000): Lock wait timeout exceeded;
                        try restarting transaction
                        
                        可以更新未加鎖的，比如
                        mysql> update test set level=11 where id=2;
                        Query OK, 1 row affected (0.00 sec)
                        Rows matched: 1 Changed: 1 Warnings: 0
--------------------------------------------------------------------------------
事務(wù)A也無法更新，因為事務(wù)B加了共享鎖
mysql> update test set level=11 where id=1;
ERROR 1205 (HY000): Lock wait timeout excee
ded; try restarting transaction
--------------------------------------------------------------------------------
                        任意一個釋放共享鎖，則獨占共享鎖的事務(wù)可以更新
                        mysql> commit;
                        Query OK, 0 rows affected (0.00 sec)
--------------------------------------------------------------------------------
事務(wù)B釋放鎖，事務(wù)A獨占，可以更新了
mysql> update test set level=11 where id=1;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0

1.2通過索引檢索數(shù)據(jù)，上排他鎖，行鎖

1.2通過索引檢索數(shù)據(jù)，上排他鎖，行鎖
SessionA                    SessionB
mysql> set autocommit=0;            mysql> set autocommit=0;
Query OK, 0 rows affected (0.02 sec)      Query OK, 0 rows affected (0.02 sec)
mysql> select * from test;           mysql> select * from test;
--------------------------------------------------------------------------------
+----+-------+-------+-------+         +----+-------+-------+-------+              
| id | name | money | level |         | id | name | money | level |
+----+-------+-------+-------+         +----+-------+-------+-------+
| 1 | tom  |  100 |   1 |         | 1 | tom  |  100 |   1 |
| 2 | jack |  200 |   2 |         | 2 | jack |  200 |   2 |
| 3 | lucas |  300 |   3 |         | 3 | lucas |  300 |   3 |
+----+-------+-------+-------+         +----+-------+-------+-------+
3 rows in set (0.00 sec)            3 rows in set (0.00 sec)
--------------------------------------------------------------------------------
對主鍵索引上排他鎖,其他事務(wù)也能獲取到共享鎖
mysql> select *from test where
id=1 for update;
+----+------+-------+-------+
| id | name | money | level |
+----+------+-------+-------+
| 1 | tom |  100 |   1 |
+----+------+-------+-------+
1 row in set (0.01 sec)
--------------------------------------------------------------------------------
                        事務(wù)B則不能繼續(xù)上排它鎖，會發(fā)生等待
                        mysql> select *from test where id=1 for update;
                        ERROR 1205 (HY000): Lock wait timeout exceeded;
                        try restarting transaction
                        
                        MORE:
                        也不能更新，因為更新也是上排它鎖
                        mysql> update test set level=2 where id=1;
                        ERROR 1205 (HY000): Lock wait timeout exceeded;
                        try restarting transaction
                        
                        也不能上共享鎖
                        mysql> select * from test where level=1 lock in share mode;
                        ERROR 1205 (HY000): Lock wait timeout exceeded;
                        try restarting transaction
--------------------------------------------------------------------------------
事務(wù)A可以更新
mysql> update test set level=11 where id=1;
Query OK, 1 row affected (0.08 sec)
Rows matched: 1 Changed: 1 Warnings: 0
--------------------------------------------------------------------------------
釋放排它鎖
mysql> commit;
Query OK, 0 rows affected (0.00 sec)
--------------------------------------------------------------------------------
                        事務(wù)A釋放鎖，事務(wù)B就可以加排它鎖了
                        mysql> select * from test where id=1 for update;
                        +----+------+-------+-------+
                        | id | name | money | level |
                        +----+------+-------+-------+
                        | 1 | tom |  100 |   1 |
                        +----+------+-------+-------+
                        1 row in set (0.00 sec)

1.3通過索引更新數(shù)據(jù)，也是上排他鎖，行鎖

對于 update,insert,delete 語句會自動加排它鎖

1.3通過索引更新數(shù)據(jù)，也是上排他鎖，行鎖
SessionA                    SessionB
mysql> set autocommit=0;            mysql> set autocommit=0;
Query OK, 0 rows affected (0.02 sec)      Query OK, 0 rows affected (0.02 sec)
mysql> select * from test;           mysql> select * from test;
--------------------------------------------------------------------------------
+----+-------+-------+-------+         +----+-------+-------+-------+              
| id | name | money | level |         | id | name | money | level |
+----+-------+-------+-------+         +----+-------+-------+-------+
| 1 | tom  |  100 |   1 |         | 1 | tom  |  100 |   1 |
| 2 | jack |  200 |   2 |         | 2 | jack |  200 |   2 |
| 3 | lucas |  300 |   3 |         | 3 | lucas |  300 |   3 |
+----+-------+-------+-------+         +----+-------+-------+-------+
3 rows in set (0.00 sec)            3 rows in set (0.00 sec)
--------------------------------------------------------------------------------
更新id=1的行，就給該行上了排它鎖，其他事務(wù)
無法更新該行
mysql> update test set level=11 where id=1;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
--------------------------------------------------------------------------------
                        事務(wù)B則不能更新id=1的行，會發(fā)生等待
                        mysql> update test set level=21 where id=1;
                        ERROR 1205 (HY000): Lock wait timeout exceeded;
                        try restarting transaction
                        
                        MORE:
                        也不能上排它鎖
                        mysql> select *from test where id=1 for update;
                        ERROR 1205 (HY000): Lock wait timeout exceeded;
                        try restarting transaction
                        
                        也不能上共享鎖
                        mysql> select * from test where level=1 lock in share mode;
                        ERROR 1205 (HY000): Lock wait timeout exceeded;
                        try restarting transaction
--------------------------------------------------------------------------------
釋放排它鎖
mysql> commit;
Query OK, 0 rows affected (0.00 sec)
--------------------------------------------------------------------------------
                        事務(wù)A釋放鎖，事務(wù)B就可以加排它鎖了
                        mysql> select * from test where id=1 for update;
                        +----+------+-------+-------+
                        | id | name | money | level |
                        +----+------+-------+-------+
                        | 1 | tom |  100 |   11|
                        +----+------+-------+-------+
                        1 row in set (0.00 sec)

2.1臟讀

//臟讀
//2.1臟讀
SessionA                    SessionB
mysql> set autocommit=0;            mysql> set autocommit=0;
Query OK, 0 rows affected (0.02 sec)      Query OK, 0 rows affected (0.02 sec)
set session transaction isolation        set session transaction isolation level read uncommitted;
level read uncommitted;             Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)      
mysql> select * from test;           mysql> select * from test;
--------------------------------------------------------------------------------
+----+-------+-------+-------+         +----+-------+-------+-------+              
| id | name | money | level |         | id | name | money | level |
+----+-------+-------+-------+         +----+-------+-------+-------+
| 1 | tom  |  100 |   1 |         | 1 | tom  |  100 |   1 |
| 2 | jack |  200 |   2 |         | 2 | jack |  200 |   2 |
| 3 | lucas |  300 |   3 |         | 3 | lucas |  300 |   3 |
+----+-------+-------+-------+         +----+-------+-------+-------+
3 rows in set (0.00 sec)            3 rows in set (0.00 sec)
--------------------------------------------------------------------------------
                        mysql> update test set level=100 where id=1;
                        Query OK, 1 row affected (0.00 sec)
                        Rows matched: 1 Changed: 1 Warnings: 0
--------------------------------------------------------------------------------
//臟讀
mysql> select *from test where id=1;
+----+------+-------+-------+
| id | name | money | level |
+----+------+-------+-------+
| 1 | tom |  100 |  100 |
+----+------+-------+-------+
1 row in set (0.00 sec)
--------------------------------------------------------------------------------
                        rollback;
                        Query OK, 0 rows affected (0.01 sec)
                        
                        mysql> select *from test where id=1;
                        +----+------+-------+-------+
                        | id | name | money | level |
                        +----+------+-------+-------+
                        | 1 | tom |  100 |   1 |
                        +----+------+-------+-------+
                        1 row in set (0.00 sec)

2.2不可重復(fù)讀

2.2不可重復(fù)讀
//臟讀
SessionA                    SessionB
mysql> set autocommit=0;            mysql> set autocommit=0;
Query OK, 0 rows affected (0.02 sec)      Query OK, 0 rows affected (0.02 sec)
set session transaction isolation        set session transaction isolation level read uncommitted;
level read uncommitted;             Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)      
mysql> select * from test;           mysql> select * from test;
--------------------------------------------------------------------------------
+----+-------+-------+-------+         +----+-------+-------+-------+              
| id | name | money | level |         | id | name | money | level |
+----+-------+-------+-------+         +----+-------+-------+-------+
| 1 | tom  |  100 |   1 |         | 1 | tom  |  100 |   1 |
| 2 | jack |  200 |   2 |         | 2 | jack |  200 |   2 |
| 3 | lucas |  300 |   3 |         | 3 | lucas |  300 |   3 |
+----+-------+-------+-------+         +----+-------+-------+-------+
3 rows in set (0.00 sec)            3 rows in set (0.00 sec)
--------------------------------------------------------------------------------
                        mysql> update test set level=100 where id=1;
                        Query OK, 1 row affected (0.00 sec)
                        Rows matched: 1 Changed: 1 Warnings: 0
--------------------------------------------------------------------------------
mysql> select *from test where id=1;
+----+------+-------+-------+
| id | name | money | level |
+----+------+-------+-------+
| 1 | tom |  100 |  100 |
+----+------+-------+-------+
1 row in set (0.00 sec)
--------------------------------------------------------------------------------
                        mysql> update test set level=1000 where id=1;
                        Query OK, 1 row affected (0.00 sec)
                        Rows matched: 1 Changed: 1 Warnings: 0
--------------------------------------------------------------------------------
//不可重復(fù)讀
//讀三次，第一次是level是1，第二次是100，第三次是1000
mysql> select *from test where id=1;
+----+------+-------+-------+
| id | name | money | level |
+----+------+-------+-------+
| 1 | tom |  100 |  1000|
+----+------+-------+-------+
1 row in set (0.00 sec)

2.3幻讀

//2.3幻讀
SessionA                    SessionB
mysql> set autocommit=0;            mysql> set autocommit=0;
Query OK, 0 rows affected (0.02 sec)      Query OK, 0 rows affected (0.02 sec)
set session transaction isolation        set session transaction isolation level read uncommitted;
level read uncommitted;             Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)      
mysql> select * from test;           mysql> select * from test;
--------------------------------------------------------------------------------
+----+-------+-------+-------+         +----+-------+-------+-------+              
| id | name | money | level |         | id | name | money | level |
+----+-------+-------+-------+         +----+-------+-------+-------+
| 1 | tom  |  100 |   1 |         | 1 | tom  |  100 |   1 |
| 2 | jack |  200 |   2 |         | 2 | jack |  200 |   2 |
| 3 | lucas |  300 |   3 |         | 3 | lucas |  300 |   3 |
+----+-------+-------+-------+         +----+-------+-------+-------+
3 rows in set (0.00 sec)            3 rows in set (0.00 sec)
--------------------------------------------------------------------------------
                        mysql> update test set level=100 where id=1;
                        Query OK, 1 row affected (0.00 sec)
                        Rows matched: 1 Changed: 1 Warnings: 0
--------------------------------------------------------------------------------
mysql> select *from test where id=1;
+----+------+-------+-------+
| id | name | money | level |
+----+------+-------+-------+
| 1 | tom |  100 |  100 |
+----+------+-------+-------+
1 row in set (0.00 sec)
--------------------------------------------------------------------------------
                        mysql> insert into test (name, money，level) VALUES                             ('tim',250，4);
                        Query OK, 1 row affected (0.01 sec)
--------------------------------------------------------------------------------
//幻讀
//讀兩次，第二次多了tim的數(shù)據(jù)
//如果是rr級別，需要使用當(dāng)前讀select * from test lock in share mode;否則因為MVCC的緣故，是讀不到tim的
mysql> select * from test;
+----+-------+-------+-------+
| id | name | money | level |
+----+-------+-------+-------+
| 1 | tom  |  100 |   1 |
| 2 | jack |  200 |   2 |
| 3 | lucas |  300 |   3 |
| 4 | tim  |  250 |   4 |
+----+-------+-------+-------+
4 row in set (0.00 sec)

3 間隙鎖(Net-Key鎖)

MVCC使RR級別下，事務(wù)當(dāng)前讀，來避免了讀情況下的幻讀問題，但如果寫更新時候呢？在范圍更新的同時，往范圍內(nèi)插入新數(shù)據(jù)，怎么辦？

于是就有了間隙鎖，在更新某個區(qū)間數(shù)據(jù)時，將會鎖定這個區(qū)間的所有記錄。例如update XXX where id between 1 and 100，就會鎖住id從1到100之間的所有的記錄。值得注意的是，在這個區(qū)間中假設(shè)某條記錄并不存在，該條記錄也會被鎖住，這時，如果另一個事務(wù)往這個區(qū)間添加數(shù)據(jù)，就必須等待上一個事務(wù)釋放鎖資源。

使用間隙鎖有兩個目的，一是防止幻讀；二是滿足其恢復(fù)和賦值的需求。

3.1范圍間隙鎖，顯式左開右閉區(qū)間

//間隙鎖(Net-Key鎖) 范圍間隙鎖，左開右閉區(qū)間
SessionA                    SessionB
mysql> set autocommit=0;            mysql> set autocommit=0;
Query OK, 0 rows affected (0.02 sec)      Query OK, 0 rows affected (0.02 sec)
     
mysql> select * from test;           mysql> select * from test;
--------------------------------------------------------------------------------
+----+-------+-------+-------+         +----+-------+-------+-------+              
| id | name | money | level |         | id | name | money | level |
+----+-------+-------+-------+         +----+-------+-------+-------+
| 1 | tom  |  100 |   1 |         | 1 | tom  |  100 |   1 |
| 2 | jack |  200 |   2 |         | 2 | jack |  200 |   2 |
| 3 | lucas |  300 |   3 |         | 3 | lucas |  300 |   3 |
+----+-------+-------+-------+         +----+-------+-------+-------+
3 rows in set (0.00 sec)            3 rows in set (0.00 sec)
--------------------------------------------------------------------------------
mysql> update test set level=0
where money between 0 and 200;
Query OK, 2 rows affected (0.02 sec)
Rows matched: 2 Changed: 2 Warnings: 0
理論上應(yīng)該鎖定[0,300)這個區(qū)間
--------------------------------------------------------------------------------
                        插入money=0等待
                        mysql> insert into test (name, money,level) VALUES ('tim',0,0);
                        ERROR 1205 (HY000): Lock wait timeout exceeded;
                        try restarting transaction
                        
                        插入money=90等待
                        mysql> insert into test (name, money,level) VALUES ('tim',90,0);
                        ERROR 1205 (HY000): Lock wait timeout exceeded;
                        try restarting transaction
                        
                        插入money=100等待
                        mysql> insert into test (name, money,level) VALUES ('tim',100,0);
                        ERROR 1205 (HY000): Lock wait timeout exceeded;
                        try restarting transaction
                        
                        插入money=299等待
                        mysql> insert into test (name, money,level) VALUES ('tim',299,0);
                        ERROR 1205 (HY000): Lock wait timeout exceeded;
                        try restarting transaction
                        
                        插入money=300 ok
                        mysql> insert into test (name, money,level) VALUES ('tim',300,0);
                        Query OK, 1 row affected (0.00 sec)

3.2單個間隙鎖隱式區(qū)間

上小節(jié)是指定update某個區(qū)間，那如果說是只update一個值呢？還會有間隙鎖么？

//間隙鎖(Net-Key鎖) 單個間隙鎖，左開右閉區(qū)間
SessionA                    SessionB
mysql> set autocommit=0;            mysql> set autocommit=0;
Query OK, 0 rows affected (0.02 sec)      Query OK, 0 rows affected (0.02 sec)
     
mysql> select * from test;           mysql> select * from test;
--------------------------------------------------------------------------------
+----+-------+-------+-------+         +----+-------+-------+-------+              
| id | name | money | level |         | id | name | money | level |
+----+-------+-------+-------+         +----+-------+-------+-------+
| 1 | tom  |  100 |   1 |         | 1 | tom  |  100 |   1 |
| 2 | jack |  200 |   2 |         | 2 | jack |  200 |   2 |
| 3 | lucas |  300 |   3 |         | 3 | lucas |  300 |   3 |
+----+-------+-------+-------+         +----+-------+-------+-------+
3 rows in set (0.00 sec)            3 rows in set (0.00 sec)
--------------------------------------------------------------------------------
mysql> update test set level=0
where money = 200;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
理論上應(yīng)該鎖定[0,300)這個區(qū)間
--------------------------------------------------------------------------------
                        插入money=0 ok
                        mysql> insert into test (name, money,level) VALUES ('tim',0,0);
                        Query OK, 1 row affected (0.00 sec)
                        
                        插入money=90 ok
                        mysql> insert into test (name, money,level) VALUES ('tim',90,0);
                        Query OK, 1 row affected (0.00 sec)
                        
                        插入money=100等待
                        mysql> insert into test (name, money,level) VALUES ('tim',100,0);
                        ERROR 1205 (HY000): Lock wait timeout exceeded;
                        try restarting transaction
                        
                        插入money=150等待
                        mysql> insert into test (name, money,level) VALUES ('tim',150,0);
                        ERROR 1205 (HY000): Lock wait timeout exceeded;
                        try restarting transaction
                        
                        插入money=200等待
                        mysql> insert into test (name, money,level) VALUES ('tim',200,0);
                        ERROR 1205 (HY000): Lock wait timeout exceeded;
                        try restarting transaction
                        
                        插入money=240等待
                        mysql> insert into test (name, money,level) VALUES ('tim',240,0);
                        ERROR 1205 (HY000): Lock wait timeout exceeded;
                        try restarting transaction
                        
                        插入money=300 ok
                        mysql> insert into test (name, money,level) VALUES ('tim',300,0);
                        Query OK, 1 row affected (0.00 sec)

當(dāng)不指定區(qū)間時，隱式的區(qū)間為索引B+數(shù)前后兩個節(jié)點的值所確定的區(qū)間，也是左開右閉，對于上述例子，就是[0,300)這個區(qū)間。

總結(jié)

到此這篇關(guān)于Mysql InnoDB鎖定機制的文章就介紹到這了,更多相關(guān)Mysql InnoDB鎖定機制內(nèi)容請搜索腳本之家以前的文章或繼續(xù)瀏覽下面的相關(guān)文章希望大家以后多多支持腳本之家！

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