mysql中一个RR模式下UPDATE锁范围扩展案例分析
发布时间：2021-12-17 12:45:45 所属栏目：MySql教程 来源：互联网
导读：本篇内容介绍了mysql中一个RR模式下UPDATE锁范围扩大案例分析的有关知识，在实际案例的操作过程中，不少人都会遇到这样的困境，接下来就让小编带领大家学习一下如何处理这些情况吧！希望大家仔细阅读，能够学有所成！ 一、前言 这里只研究下锁的模式,借用叶
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本篇内容介绍了“mysql中一个RR模式下UPDATE锁范围扩大案例分析”的有关知识，在实际案例的操作过程中，不少人都会遇到这样的困境，接下来就让小编带领大家学习一下如何处理这些情况吧！希望大家仔细阅读，能够学有所成！ 一、前言 这里只研究下锁的模式,借用叶老师的表和语句 mysql> select * from t1; +----+----+----+----+ | c1 | c2 | c3 | c4 | +----+----+----+----+ | 0 | 0 | 0 | 0 | | 1 | 1 | 1 | 0 | | 3 | 3 | 3 | 0 | | 4 | 2 | 2 | 0 | | 6 | 8 | 5 | 0 | | 7 | 6 | 6 | 10 | | 10 | 10 | 4 | 0 | +----+----+----+----+ CREATE TABLE `t1` ( `c1` int(10) unsigned NOT NULL DEFAULT '0', `c2` int(10) unsigned NOT NULL DEFAULT '0', `c3` int(10) unsigned NOT NULL DEFAULT '0', `c4` int(10) unsigned NOT NULL DEFAULT '0', PRIMARY KEY (`c1`), KEY `c2` (`c2`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 二、RR模式下的锁模式 我们先来看看下面两个语句的执行计划 mysql> desc update t1 set c4=123 where c2>=8; +----+-------------+-------+------------+-------+---------------+------+---------+-------+------+----------+------------------------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+-------+---------------+------+---------+-------+------+----------+------------------------------+ | 1 | UPDATE | t1 | NULL | range | c2 | c2 | 4 | const | 2 | 100.00 | Using where; Using temporary | +----+-------------+-------+------------+-------+---------------+------+---------+-------+------+----------+------------------------------+ mysql> desc update t1 set c4=123 where c2>=6; +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+------------------------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+------------------------------+ | 1 | UPDATE | t1 | NULL | index | c2 | PRIMARY | 4 | NULL | 7 | 100.00 | Using where; Using temporary | +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+------------------------------+ 下面两个语句的执行计划不一致，主要注意 type:index和range key:PRIMARY和c2 我们先要清楚type:index和range的区别 这里借用我以前写的一篇文章 http://blog.itpub.net/7728585/viewspace-2139010/ type:index 不使用索引B+树结构,只使用索引叶子结点链表结构进行扫描，我们知道在索引的叶子结点有一个叶子结点之间的双向指针， 并且叶子结点的数据是排序好的。他和ALL的方式类似，访问效率并不高，其主要的应用场景为用于避免order by使用using filesort 也就是避免排序。他是一种访问数据的方式，和range、const、ref、eq_ref等一样。 type:range 显然用于范围查询比如> between 等，其访问方式是考虑到索引的B+树结构的，需要通过根结点-->分支节点-->叶子结点的顺序访问 其实const、ref、eq_ref等一样也需要这样的定位过程。 我大概画一个图，示意图而已，但是足以解释我的意思 mysql中一个RR模式下UPDATE锁范围扩大案例分析 1.jpg 剩下我们需要考虑RR模式下，如下语句有哪些所结构： mysql> desc update t1 set c4=123 where c2>=6; +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+------------------------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+------------------------------+ | 1 | UPDATE | t1 | NULL | index | c2 | PRIMARY | 4 | NULL | 7 | 100.00 | Using where; Using temporary | +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+------------------------------+ RECORD LOCKS space id 532 page no 3 n bits 80 index PRIMARY of table `test`.`t1` trx id 348084 lock_mode X(LOCK_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 2 PHYSICAL RECORD: n_fields 6; compact format; info bits 0 0: len 4; hex 00000000; asc ;; 1: len 6; hex 000000054abd; asc J ;; 2: len 7; hex ba00000e180110; asc ;; 3: len 4; hex 00000000; asc ;; 4: len 4; hex 00000000; asc ;; 5: len 4; hex 00000000; asc ;; Record lock, heap no 3 PHYSICAL RECORD: n_fields 6; compact format; info bits 0 0: len 4; hex 00000001; asc ;; 1: len 6; hex 000000054abd; asc J ;; 2: len 7; hex ba00000e18011d; asc ;; 3: len 4; hex 00000001; asc ;; 4: len 4; hex 00000001; asc ;; 5: len 4; hex 00000000; asc ;; Record lock, heap no 4 PHYSICAL RECORD: n_fields 6; compact format; info bits 0 0: len 4; hex 00000003; asc ;; 1: len 6; hex 000000054abd; asc J ;; 2: len 7; hex ba00000e18012a; asc *;; 3: len 4; hex 00000003; asc ;; 4: len 4; hex 00000003; asc ;; 5: len 4; hex 00000000; asc ;; Record lock, heap no 5 PHYSICAL RECORD: n_fields 6; compact format; info bits 0 0: len 4; hex 00000004; asc ;; 1: len 6; hex 000000054abd; asc J ;; 2: len 7; hex ba00000e180137; asc 7;; 3: len 4; hex 00000002; asc ;; 4: len 4; hex 00000002; asc ;; 5: len 4; hex 00000000; asc ;; Record lock, heap no 6 PHYSICAL RECORD: n_fields 6; compact format; info bits 0 0: len 4; hex 00000006; asc ;; 1: len 6; hex 000000054fb4; asc O ;; 2: len 7; hex 3300000c430b49; asc 3 C I;; 3: len 4; hex 00000008; asc ;; 4: len 4; hex 00000005; asc ;; 5: len 4; hex 0000007b; asc {;; Record lock, heap no 7 PHYSICAL RECORD: n_fields 6; compact format; info bits 0 0: len 4; hex 00000007; asc ;; 1: len 6; hex 000000054fb4; asc O ;; 2: len 7; hex 3300000c430b6b; asc 3 C k;; 3: len 4; hex 00000006; asc ;; 4: len 4; hex 00000006; asc ;; 5: len 4; hex 0000007b; asc {;; Record lock, heap no 8 PHYSICAL RECORD: n_fields 6; compact format; info bits 0 0: len 4; hex 0000000a; asc ;; 1: len 6; hex 000000054fb4; asc O ;; 2: len 7; hex 3300000c430b8d; asc 3 C ;; 3: len 4; hex 0000000a; asc ;; 4: len 4; hex 00000004; asc ;; 5: len 4; hex 0000007b; asc {;; 我们这里先不考虑表级意向锁，只考虑这里打印出来的锁结构 行锁为：lock_mode X(LOCK_X)|LOCK_ORDINARY(next key lock) 同时我们注意到 0: len 8; hex 73757072656d756d; asc supremum 那么我们用一张图来表示 mysql中一个RR模式下UPDATE锁范围扩大案例分析 2.jpg 实际上我们从图中可以看出这种情况下RR模式下是主键上所有的行都加上了NEXT_KEY LOCK,所以你其他任何DML操作都会锁定 那么如下语句的锁结构呢？ mysql> desc update t1 set c4=123 where c2>=8; +----+-------------+-------+------------+-------+---------------+------+---------+-------+------+----------+------------------------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+-------+---------------+------+---------+-------+------+----------+------------------------------+ | 1 | UPDATE | t1 | NULL | range | c2 | c2 | 4 | const | 2 | 100.00 | Using where; Using temporary | +----+-------------+-------+------------+-------+---------------+------+---------+-------+------+----------+------------------------------+ 1 row in set (0.01 sec) 如下： -----TRX NO:348661 LOCK STRUCT(1)(Add by gaopeng) TABLE LOCK table `test`.`t1` trx id 348661 lock mode IX -----TRX NO:348661 LOCK STRUCT(1)(Add by gaopeng) RECORD LOCKS space id 532 page no 4 n bits 80 index c2 of table `test`.`t1` trx id 348661 lock_mode X(LOCK_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 6 PHYSICAL RECORD: n_fields 2; compact format; info bits 0 0: len 4; hex 00000008; asc ;; 1: len 4; hex 00000006; asc ;; Record lock, heap no 8 PHYSICAL RECORD: n_fields 2; compact format; info bits 0 0: len 4; hex 0000000a; asc ;; 1: len 4; hex 0000000a; asc ;; -----TRX NO:348661 LOCK STRUCT(1)(Add by gaopeng) RECORD LOCKS space id 532 page no 3 n bits 80 index PRIMARY of table `test`.`t1` trx id 348661 lock_mode X(LOCK_X) locks rec but not gap(LOCK_REC_NOT_GAP) Record lock, heap no 6 PHYSICAL RECORD: n_fields 6; compact format; info bits 0 0: len 4; hex 00000006; asc ;; 1: len 6; hex 0000000551f5; asc Q ;; 2: len 7; hex 71000002700ad1; asc q p ;; 3: len 4; hex 00000008; asc ;; 4: len 4; hex 00000005; asc ;; 5: len 4; hex 0000007b; asc {;; Record lock, heap no 8 PHYSICAL RECORD: n_fields 6; compact format; info bits 0 0: len 4; hex 0000000a; asc ;; 1: len 6; hex 0000000551f5; asc Q ;; 2: len 7; hex 71000002700af3; asc q p ;; 3: len 4; hex 0000000a; asc ;; 4: len 4; hex 00000004; asc ;; 5: len 4; hex 0000007b; asc {;; 我们可以清晰的观察到INDEX c2上包含 lock_mode X(LOCK_X)|LOCK_ORDINARY(next key lock) 其行包含了 C2:8/C1:6 C2:10/C2:10 还包含 supremum 同时传递到了主键PRIMARY锁结构为 lock_mode X(LOCK_X)|rec but not gap(LOCK_REC_NOT_GAP) 也就是主键上只是锁定了C1:6 C1:10这两行，并且不是gap lock，如果需要画图就是如下: mysql中一个RR模式下UPDATE锁范围扩大案例分析 3.jpg 我们可以发现锁定的范围小了很多很多，这种情况如下语句： select * from t1 where c1 = 7 for update; (这里叶老师写的c2=7不知道是不是写错了) 是可以完成的，因为不会落到PRIMARY的锁定范围内。 三、RC模式下的锁定模式 这里只是看看RC模式的锁定结构如下： mysql> desc update t1 set c4=123 where c2>=6; +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+------------------------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+------------------------------+ | 1 | UPDATE | t1 | NULL | index | c2 | PRIMARY | 4 | NULL | 7 | 100.00 | Using where; Using temporary | +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+------------------------------+ 1 row in set (0.22 sec) -----TRX NO:348596 LOCK STRUCT(1)(Add by gaopeng) RECORD LOCKS space id 532 page no 3 n bits 80 index PRIMARY of table `test`.`t1` trx id 348596 lock_mode X(LOCK_X) locks rec but not gap(LOCK_REC_NOT_GAP) Record lock, heap no 6 PHYSICAL RECORD: n_fields 6; compact format; info bits 0 0: len 4; hex 00000006; asc ;; 1: len 6; hex 0000000551b4; asc Q ;; 2: len 7; hex 3300000c430c03; asc 3 C ;; 3: len 4; hex 00000008; asc ;; 4: len 4; hex 00000005; asc ;; 5: len 4; hex 0000007b; asc {;; Record lock, heap no 7 PHYSICAL RECORD: n_fields 6; compact format; info bits 0 0: len 4; hex 00000007; asc ;; 1: len 6; hex 0000000551b4; asc Q ;; 2: len 7; hex 3300000c430c25; asc 3 C %;; 3: len 4; hex 00000006; asc ;; 4: len 4; hex 00000006; asc ;; 5: len 4; hex 0000007b; asc {;; Record lock, heap no 8 PHYSICAL RECORD: n_fields 6; compact format; info bits 0 0: len 4; hex 0000000a; asc ;; 1: len 6; hex 0000000551b4; asc Q ;; 2: len 7; hex 3300000c430c47; asc 3 C G;; 3: len 4; hex 0000000a; asc ;; 4: len 4; hex 00000004; asc ;; 5: len 4; hex 0000007b; asc {;; 我们可以清晰的看到RC模式下不考虑隐含锁的情况下只是锁定了PRIMARY的相应的行： lock_mode X(LOCK_X) locks|rec but not gap(LOCK_REC_NOT_GAP) 注意这里NOT GAP “mysql中一个RR模式下UPDATE锁范围扩大案例分析”的内容就介绍到这里了，感谢大家的阅读。如果想了解更多行业相关的知识可以关注亿速云网站，小编将为大家输出更多高质量的实用文章！ （编辑：源码门户网） 【声明】本站内容均来自网络，其相关言论仅代表作者个人观点，不代表本站立场。若无意侵犯到您的权利，请及时与联系站长删除相关内容! |
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