MySQL 并发，它是如何工作的，我是否需要在我的应用程序中处理它 [英] MySQL concurrency, how does it work and do I need to handle it in my application

问题描述

我目前正在运行一个 MySQL 数据库.我所有的表都使用表引擎 InnoDB.

I am currently running a MySQL database. All of my tables are using the Table Engine InnoDB.

登录我的应用程序的每个人都可以查看记录，我担心在某些时候两个用户可能会同时更新或插入记录.MySQL 是否优雅地处理了这种类型的并发问题，还是我必须将其编程到我的代码中?

Everyone who logs into my application can view records and I am worried that at some point two users might update or insert a record at the same time. Does MySQL handle this type of concurrency issue gracefully, or is this something that I am going to have to program into my code?

如果我必须将它编程到我的代码中，您将如何处理这样的并发情况?

If I do have to program it into my code how do you go about handling a concurrency case like this?

推荐答案

SQL 语句是原子的.也就是说，如果你执行这样的事情:

SQL statements are atomic. That is, if you execute something like this:

UPDATE Cars SET Sold = Sold + 1

在此声明期间，没有人可以更改 Sold 变量.它总是加 1，即使其他人正在同时执行相同的语句.

Nobody can change the Sold variable during this statement. It is always incremented by 1, even if somebody else is executing the same statement concurrently.

如果你有相互依赖的语句，就会出现问题:

The problem occurs if you have statements that depend on each other:

a = SELECT Sold FROM Cars;
UPDATE Cars SET Sold = a + 1;

在这些查询之间，另一个用户可以更改表 Cars 并更新 Sold.为了防止这种情况，请将其包装在一个事务中:

Between these queries, another user can change the table Cars and update Sold. To prevent this, wrap it in a transaction:

BEGIN;
a = SELECT Sold FROM Cars;
UPDATE Cars SET Sold = a + 1;
COMMIT;

InnoDB 支持事务，但 MyISAM 不支持.

Transactions are supported by InnoDB, but not by MyISAM.

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