为什么具有单事务的mysqldump比没有事务的mysqldump更一致?

问题描述

限时删除！！

我已经阅读了手册，并提到每个事务在开始进行转储之前都会添加一个BEGIN语句.有人可以用更容易理解的方式阐述这一点吗?

I have gone through the manual and it was mentioned that every transaction will add a BEGIN statement before it starts taking the dump. Can someone elaborate this in a more understandable manner?

这是我读到的:

可以详细说明一下吗?

推荐答案

由于转储在一个事务中，因此您可以获得数据库中所有表的一致视图.最好用一个反例来解释.假设您转储具有两个表Orders和OrderLines

Since the dump is in one transaction, you get a consistent view of all the tables in the database. This is probably best explained by a counterexample. Say you dump a database with two tables, Orders and OrderLines

1. 您无需进行单个交易即可开始转储.
2. 另一个进程在Orders表中插入一行.
3. 另一个进程在OrderLines表中插入一行.
4. 转储处理OrderLines表.
5. 另一个进程将删除Orders和OrderLines记录.
6. 转储处理Orders表.

1. You start the dump without a single transaction.
2. Another process inserts a row into the Orders table.
3. Another process inserts a row into the OrderLines table.
4. The dump processes the OrderLines table.
5. Another process deletes the Orders and OrderLines records.
6. The dump processes the Orders table.

在此示例中，您的转储将具有OrderLines的行，但没有Orders的行.如果Orders和OrderLines之间有外键，则数据将处于不一致状态，并且还原时将失败.

In this example, your dump would have the rows for OrderLines, but not Orders. The data would be in an inconsistent state and would fail on restore if there were a foreign key between Orders and OrderLines.

如果您是在单个事务中完成的，则转储将既没有顺序也没有行(但是将是一致的)，因为在事务开始之后，两者都被插入然后被删除了.

If you had done it in a single transaction, the dump would have neither the order or the lines (but it would be consistent) since both were inserted then deleted after the transaction began.

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