MySQL语句加锁的实现分析

2024-10-09 05:38:28

摘要： MySQL两条SQL语句锁的分析

看一下下面的SQL语句加什么锁

SLQ1：select * from t1 where id = 10;
SQL2：delete from t1 where id = 10;

（1）id 是不是主键

（2）当前系统的隔离级别是什么

（3）id列如果不是主键，那么id列上有索引吗

（4）id列上如果有二级索引，那么这个索引是二级索引吗

（5）两个SQL的执行计划是什么？索引扫描还是全表扫描

实际的执行计划需要根据MySQL的输出为准

组合一：id列是主键，RC隔离级别
组合二：id列是二级唯一索引，RC隔离级别
组合三：id列是二级非唯一索引，RC隔离级别
组合四：id列没有索引，RC隔离级别
组合五：id列是主键，RR隔离级别
组合六：id列是二级唯一索引，RR隔离级别
组合七：id列是二级非唯一索引，RR隔离级别
组合八：id列上没有索引，RR隔离级别

Serializable隔离级别

在RR RC隔离级别下，SQL1：select 均不加锁，采用的是快照读；以下仅讨论SQL2：delete操作的加锁
Percona

组合一：id主键+RC
Percona

---TRANSACTION 1286310, ACTIVE 9 sec
2 lock struct(s), heap size 360, 1 row lock(s), undo log entries 1
MySQL thread id 341, OS thread handle 0x7f4d540d0700, query id 4510972 localhost root cleaning up
TABLE LOCK table `test`.`t1` trx id 1286310 lock mode IX
RECORD LOCKS space id 29 page no 3 n bits 80 index `PRIMARY` of table `test`.`t1` trx id 1286310 lock_mode X locks rec but not gap

MySQL

---TRANSACTION 5936, ACTIVE 171 sec
2 lock struct(s), heap size 360, 1 row lock(s), undo log entries 1
MySQL thread id 2, OS thread handle 0x7f5677201700, query id 364 localhost root
TABLE LOCK table `test`.`t1` trx id 5936 lock mode IX
RECORD LOCKS space id 6 page no 3 n bits 80 index `PRIMARY` of table `test`.`t1` trx id 5936 lock_mode X locks rec but not gap
Record lock, heap no 5 PHYSICAL RECORD: n_fields 4; compact format; info bits 32
 0: len 4; hex 8000000a; asc   ;;
 1: len 6; hex 000000001730; asc   0;;
 2: len 7; hex 26000001550110; asc &  U ;;
 3: len 1; hex 61; asc a;;

组合二：id唯一索引+RC
在唯一索引上的更新需要两个X锁，一个对应唯一索引id=10 记录，一个对应于聚簇索引name='d'的记录
Percona

---TRANSACTION 1286327, ACTIVE 3 sec
3 lock struct(s), heap size 360, 2 row lock(s), undo log entries 1
MySQL thread id 344, OS thread handle 0x7f4d5404e700, query id 4510986 localhost root cleaning up
TABLE LOCK table `test`.`t2` trx id 1286327 lock mode IX
RECORD LOCKS space id 30 page no 4 n bits 80 index `id` of table `test`.`t2` trx id 1286327 lock_mode X locks rec but not gap
RECORD LOCKS space id 30 page no 3 n bits 80 index `PRIMARY` of table `test`.`t2` trx id 1286327 lock_mode X locks rec but not gap

MySQL

---TRANSACTION 5938, ACTIVE 3 sec
3 lock struct(s), heap size 360, 2 row lock(s), undo log entries 1
MySQL thread id 2, OS thread handle 0x7f5677201700, query id 374 localhost root
TABLE LOCK table `test`.`t2` trx id 5938 lock mode IX
RECORD LOCKS space id 7 page no 4 n bits 80 index `id` of table `test`.`t2` trx id 5938 lock_mode X locks rec but not gap
Record lock, heap no 7 PHYSICAL RECORD: n_fields 2; compact format; info bits 32
 0: len 4; hex 8000000a; asc   ;;
 1: len 1; hex 64; asc d;;

RECORD LOCKS space id 7 page no 3 n bits 80 index `PRIMARY` of table `test`.`t2` trx id 5938 lock_mode X locks rec but not gap
Record lock, heap no 7 PHYSICAL RECORD: n_fields 4; compact format; info bits 32
 0: len 1; hex 64; asc d;;
 1: len 6; hex 000000001732; asc   2;;
 2: len 7; hex 27000001560110; asc '  V ;;
 3: len 4; hex 8000000a; asc   ;;

组合三：id非唯一索引+RC
ID列为普通索引，那么对应的所有满足SQL查询条件的记录，都会被加锁；同时，这些记录在主键索引上的记录，也会被加锁
Percona

---TRANSACTION 1286339, ACTIVE 9 sec
3 lock struct(s), heap size 360, 4 row lock(s), undo log entries 2
MySQL thread id 347, OS thread handle 0x7f4b67fff700, query id 4511015 localhost root cleaning up
TABLE LOCK table `test`.`t3` trx id 1286339 lock mode IX
RECORD LOCKS space id 31 page no 4 n bits 80 index `idx_key` of table `test`.`t3` trx id 1286339 lock_mode X locks rec but not gap
RECORD LOCKS space id 31 page no 3 n bits 80 index `PRIMARY` of table `test`.`t3` trx id 1286339 lock_mode X locks rec but not gap

MySQL

---TRANSACTION 5940, ACTIVE 3 sec
3 lock struct(s), heap size 360, 4 row lock(s), undo log entries 2
MySQL thread id 2, OS thread handle 0x7f5677201700, query id 378 localhost root
TABLE LOCK table `test`.`t3` trx id 5940 lock mode IX
RECORD LOCKS space id 8 page no 4 n bits 80 index `idx_key` of table `test`.`t3` trx id 5940 lock_mode X locks rec but not gap
Record lock, heap no 4 PHYSICAL RECORD: n_fields 2; compact format; info bits 32
 0: len 4; hex 8000000a; asc   ;;
 1: len 1; hex 62; asc b;;

Record lock, heap no 5 PHYSICAL RECORD: n_fields 2; compact format; info bits 32
 0: len 4; hex 8000000a; asc   ;;
 1: len 1; hex 64; asc d;;

RECORD LOCKS space id 8 page no 3 n bits 80 index `PRIMARY` of table `test`.`t3` trx id 5940 lock_mode X locks rec but not gap
Record lock, heap no 4 PHYSICAL RECORD: n_fields 4; compact format; info bits 32
 0: len 1; hex 62; asc b;;
 1: len 6; hex 000000001734; asc   4;;
 2: len 7; hex 28000001570110; asc (  W ;;
 3: len 4; hex 8000000a; asc   ;;

Record lock, heap no 5 PHYSICAL RECORD: n_fields 4; compact format; info bits 32
 0: len 1; hex 64; asc d;;
 1: len 6; hex 000000001734; asc   4;;
 2: len 7; hex 28000001570132; asc (  W 2;;
 3: len 4; hex 8000000a; asc   ;;

组合四：id无索引+RC
Percona

---TRANSACTION 1286373, ACTIVE 5 sec
2 lock struct(s), heap size 360, 2 row lock(s), undo log entries 2
MySQL thread id 348, OS thread handle 0x7f4d54193700, query id 4511037 localhost root cleaning up
TABLE LOCK table `test`.`t4` trx id 1286373 lock mode IX
RECORD LOCKS space id 33 page no 3 n bits 80 index `PRIMARY` of table `test`.`t4` trx id 1286373 lock_mode X locks rec but not gap

MySQL

---TRANSACTION 5946, ACTIVE 2 sec
2 lock struct(s), heap size 360, 2 row lock(s), undo log entries 2
MySQL thread id 2, OS thread handle 0x7f5677201700, query id 382 localhost root
TABLE LOCK table `test`.`t4` trx id 5946 lock mode IX
RECORD LOCKS space id 9 page no 3 n bits 80 index `PRIMARY` of table `test`.`t4` trx id 5946 lock_mode X locks rec but not gap
Record lock, heap no 3 PHYSICAL RECORD: n_fields 4; compact format; info bits 32
 0: len 1; hex 62; asc b;;
 1: len 6; hex 00000000173a; asc   :;;
 2: len 7; hex 2b0000015a0110; asc +  Z ;;
 3: len 4; hex 8000000a; asc   ;;

Record lock, heap no 5 PHYSICAL RECORD: n_fields 4; compact format; info bits 32
 0: len 1; hex 64; asc d;;
 1: len 6; hex 00000000173a; asc   :;;
 2: len 7; hex 2b0000015a012c; asc +  Z ,;;
 3: len 4; hex 8000000a; asc   ;;

组合五：id主键+RR
参考组合一

组合六：id唯一索引+RR
参考组合二

组合七：id非唯一索引+RR
Percona

---TRANSACTION 1592633, ACTIVE 24 sec
4 lock struct(s), heap size 1184, 5 row lock(s), undo log entries 2
MySQL thread id 794, OS thread handle 0x7f4d5404e700, query id 7801799 localhost root cleaning up
Trx read view will not see trx with id >= 1592634, sees < 1592634
TABLE LOCK table `test`.`t3` trx id 1592633 lock mode IX
RECORD LOCKS space id 31 page no 4 n bits 80 index `idx_key` of table `test`.`t3` trx id 1592633 lock_mode X
RECORD LOCKS space id 31 page no 3 n bits 80 index `PRIMARY` of table `test`.`t3` trx id 1592633 lock_mode X locks rec but not gap
RECORD LOCKS space id 31 page no 4 n bits 80 index `idx_key` of table `test`.`t3` trx id 1592633 lock_mode X locks gap before rec

MySQL

---TRANSACTION 5985, ACTIVE 7 sec
4 lock struct(s), heap size 1184, 5 row lock(s), undo log entries 2
MySQL thread id 12, OS thread handle 0x7f56770fd700, query id 500 localhost root
TABLE LOCK table `test`.`t3` trx id 5985 lock mode IX
RECORD LOCKS space id 8 page no 4 n bits 80 index `idx_key` of table `test`.`t3` trx id 5985 lock_mode X
Record lock, heap no 4 PHYSICAL RECORD: n_fields 2; compact format; info bits 32
 0: len 4; hex 8000000a; asc   ;;
 1: len 1; hex 64; asc d;;

Record lock, heap no 5 PHYSICAL RECORD: n_fields 2; compact format; info bits 32
 0: len 4; hex 8000000a; asc   ;;
 1: len 1; hex 62; asc b;;

RECORD LOCKS space id 8 page no 3 n bits 80 index `PRIMARY` of table `test`.`t3` trx id 5985 lock_mode X locks rec but not gap
Record lock, heap no 4 PHYSICAL RECORD: n_fields 4; compact format; info bits 32
 0: len 1; hex 64; asc d;;
 1: len 6; hex 000000001761; asc   a;;
 2: len 7; hex 3f0000016d0132; asc ?  m 2;;
 3: len 4; hex 8000000a; asc   ;;

Record lock, heap no 5 PHYSICAL RECORD: n_fields 4; compact format; info bits 32
 0: len 1; hex 62; asc b;;
 1: len 6; hex 000000001761; asc   a;;
 2: len 7; hex 3f0000016d0110; asc ?  m ;;
 3: len 4; hex 8000000a; asc   ;;

RECORD LOCKS space id 8 page no 4 n bits 80 index `idx_key` of table `test`.`t3` trx id 5985 lock_mode X locks gap before rec
Record lock, heap no 8 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
 0: len 4; hex 8000000b; asc   ;;
 1: len 1; hex 66; asc f;;

组合八：id无索引+RR
Percona

---TRANSACTION 1592639, ACTIVE 4 sec
2 lock struct(s), heap size 360, 7 row lock(s), undo log entries 2
MySQL thread id 794, OS thread handle 0x7f4d5404e700, query id 7801804 localhost root cleaning up
TABLE LOCK table `test`.`t4` trx id 1592639 lock mode IX
RECORD LOCKS space id 33 page no 3 n bits 80 index `PRIMARY` of table `test`.`t4` trx id 1592639 lock_mode X

MySQL

---TRANSACTION 6000, ACTIVE 3 sec
2 lock struct(s), heap size 360, 7 row lock(s), undo log entries 2
MySQL thread id 12, OS thread handle 0x7f56770fd700, query id 546 localhost root
TABLE LOCK table `test`.`t4` trx id 6000 lock mode IX
RECORD LOCKS space id 9 page no 3 n bits 80 index `PRIMARY` of table `test`.`t4` trx id 6000 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 2 PHYSICAL RECORD: n_fields 4; compact format; info bits 0
 0: len 1; hex 61; asc a;;
 1: len 6; hex 000000001722; asc   ";;
 2: len 7; hex 9e0000014e0110; asc   N ;;
 3: len 4; hex 8000000f; asc   ;;

Record lock, heap no 3 PHYSICAL RECORD: n_fields 4; compact format; info bits 32
 0: len 1; hex 62; asc b;;
 1: len 6; hex 000000001770; asc   p;;
 2: len 7; hex 47000001730110; asc G  s ;;
 3: len 4; hex 8000000a; asc   ;;

Record lock, heap no 4 PHYSICAL RECORD: n_fields 4; compact format; info bits 0
 0: len 1; hex 63; asc c;;
 1: len 6; hex 000000001722; asc   ";;
 2: len 7; hex 9e0000014e0122; asc   N ";;
 3: len 4; hex 80000006; asc   ;;

Record lock, heap no 5 PHYSICAL RECORD: n_fields 4; compact format; info bits 32
 0: len 1; hex 64; asc d;;
 1: len 6; hex 000000001770; asc   p;;
 2: len 7; hex 4700000173012c; asc G  s ,;;
 3: len 4; hex 8000000a; asc   ;;

Record lock, heap no 6 PHYSICAL RECORD: n_fields 4; compact format; info bits 0
 0: len 1; hex 66; asc f;;
 1: len 6; hex 000000001722; asc   ";;
 2: len 7; hex 9e0000014e0134; asc   N 4;;
 3: len 4; hex 8000000b; asc   ;;

Record lock, heap no 7 PHYSICAL RECORD: n_fields 4; compact format; info bits 0
 0: len 2; hex 7a7a; asc zz;;
 1: len 6; hex 000000001722; asc   ";;
 2: len 7; hex 9e0000014e013d; asc   N =;;
 3: len 4; hex 80000002; asc   ;;

组合九：Serializable

针对前面提到的简单的SQL，最后一个情况：Serializable隔离级别。对于SQL2：delete from t1 where id = 10; 来说，Serializable隔离级别与Repeatable Read隔离级别完全一致，因此不做介绍。

Serializable隔离级别，影响的是SQL1：select * from t1 where id = 10; 这条SQL，在RC，RR隔离级别下，都是快照读，不加锁。但是在Serializable隔离级别，SQL1会加读锁，也就是说快照读不复存在，MVCC并发控制降级为Lock-Based CC。

结论：在MySQL/InnoDB中，所谓的读不加锁，并不适用于所有的情况，而是隔离级别相关的。Serializable隔离级别，读不加锁就不再成立，所有的读操作，都是当前读。

详解MySQL中的死锁情况以及对死锁的处理方法

当多个事务同时持有和请求同一资源上的锁而产生循环依赖的时候就产生了死锁.死锁发生在事务试图以不同的顺序锁定资源.以StockPrice表上的两个事务为例: 事务1 START TRANSACTION; UPDATE StockPrice SET close = 45.50 WHERE stock_id = 4 and date = '2002-05-01'; UPDATE StockPrice SET close = 19.80 WHERE stock_id = 3 and date = '20
通过mysql show processlist 命令检查mysql锁的方法

processlist命令的输出结果显示了有哪些线程在运行,可以帮助识别出有问题的查询语句,两种方式使用这个命令. 1. 进入mysql/bin目录下输入mysqladmin processlist; 2. 启动mysql,输入show processlist; 如果有SUPER权限,则可以看到全部的线程,否则,只能看到自己发起的线程(这是指,当前对应的MySQL帐户运行的线程). 得到数据形式如下(只截取了三条): mysql> show processlist; +---
mysql 数据库死锁原因及解决办法

死锁(Deadlock) 所谓死锁:是指两个或两个以上的进程在执行过程中,因争夺资源而造成的一种互相等待的现象,若无外力作用,它们都将无法推进下去.此时称系统处于死锁状态或系统产生了死锁,这些永远在互相等待的进程称为死锁进程.由于资源占用是互斥的,当某个进程提出申请资源后,使得有关进程在无外力协助下,永远分配不到必需的资源而无法继续运行,这就产生了一种特殊现象死锁. 一种情形,此时执行程序中两个或多个线程发生永久堵塞(等待),每个线程都在等待被其他线程占用并堵塞了的资源.例如,如果线程A锁住了记
MySQL死锁问题分析及解决方法实例详解

MySQL死锁问题是很多程序员在项目开发中常遇到的问题,现就MySQL死锁及解决方法详解如下: 1.MySQL常用存储引擎的锁机制 MyISAM和MEMORY采用表级锁(table-level locking) BDB采用页面锁(page-level locking)或表级锁,默认为页面锁 InnoDB支持行级锁(row-level locking)和表级锁,默认为行级锁 2.各种锁特点表级锁:开销小,加锁快;不会出现死锁;锁定粒度大,发生锁冲突的概率最高,并发度最低行级锁:开销大,加锁慢;
MySQL Innodb表导致死锁日志情况分析与归纳

案例描述在定时脚本运行过程中,发现当备份表格的sql语句与删除该表部分数据的sql语句同时运行时,mysql会检测出死锁,并打印出日志.两个sql语句如下:(1)insert into backup_table select * from source_table(2)DELETE FROM source_table WHERE Id>5 AND titleWeight<32768 AND joinTime<'$daysago_1week'teamUser表的表结构如下:PRIMARY
mysql锁表和解锁语句分享

页级的典型代表引擎为BDB. 表级的典型代表引擎为MyISAM,MEMORY以及很久以前的ISAM. 行级的典型代表引擎为INNODB. -我们实际应用中用的最多的就是行锁. 行级锁的优点如下: 1).当很多连接分别进行不同的查询时减小LOCK状态. 2).如果出现异常,可以减少数据的丢失.因为一次可以只回滚一行或者几行少量的数据. 行级锁的缺点如下: 1).比页级锁和表级锁要占用更多的内存. 2).进行查询时比页级锁和表级锁需要的I/O要多,所以我们经常把行级锁用在写操作而不是读操作. 3).
Mysql数据库锁定机制详细介绍

前言为了保证数据的一致完整性,任何一个数据库都存在锁定机制.锁定机制的优劣直接应想到一个数据库系统的并发处理能力和性能,所以锁定机制的实现也就成为了各种数据库的核心技术之一.本章将对MySQL中两种使用最为频繁的存储引擎MyISAM和Innodb各自的锁定机制进行较为详细的分析. MySQL锁定机制简介数据库锁定机制简单来说就是数据库为了保证数据的一致性而使各种共享资源在被并发访问访问变得有序所设计的一种规则.对于任何一种数据库来说都需要有相应的锁定机制,所以MySQL自然也不能例外.MyS
MySQL行级锁、表级锁、页级锁详细介绍

页级:引擎 BDB.表级:引擎 MyISAM , 理解为锁住整个表,可以同时读,写不行行级:引擎 INNODB , 单独的一行记录加锁表级,直接锁定整张表,在你锁定期间,其它进程无法对该表进行写操作.如果你是写锁,则其它进程则读也不允许行级,,仅对指定的记录进行加锁,这样其它进程还是可以对同一个表中的其它记录进行操作.页级,表级锁速度快,但冲突多,行级冲突少,但速度慢.所以取了折衷的页级,一次锁定相邻的一组记录. MySQL 5.1支持对MyISAM和MEMORY表进行表级锁定,对BDB表进行
mysql 锁表锁行语句分享(MySQL事务处理)

复制代码代码如下: mysql_query("set autocommit=0"); $list_one = $db->fetch_first("select * from prizes where id = ".$id." FOR UPDATE"); $db->query("DELETE from prizes WHERE id =".$list_one['id']); mysql_query("co
MYSQL锁表问题的解决方法

本文实例讲述了MYSQL锁表问题的解决方法.分享给大家供大家参考,具体如下: 很多时候!一不小心就锁表!这里讲解决锁表终极方法! 案例一 mysql>show processlist; 参看sql语句一般少的话 mysql>kill thread_id; 就可以解决了 kill掉第一个锁表的进程, 依然没有改善. 既然不改善, 咱们就想办法将所有锁表的进程kill掉吧, 简单的脚本如下. #!/bin/bash mysql - u root - e " show processli

MySQL语句加锁的实现分析

相关推荐

随机推荐