READ_UNCOMMITTED与没有交易？ [英] READ_UNCOMMITTED vs No transactions?

问题描述

在READ_UNCOMMITTED隔离模式下执行SQL与执行SQL之间有什么区别？

What's the difference between executing SQL outside of a transaction versus executing it under READ_UNCOMMITTED isolation mode?

澄清：我试图了解 java.sql.Connection.TRANSACTION_NONE之间的差异和 java.sql.Connection。 TRANSACTION_READ_UNCOMMITTED

推荐答案

TRANSACTION_NONE 表示连接不支持事务，并且对该连接强加事务语义的任何尝试都将失败。我不能看到这有用，除非你使用一个假数据库，如CSV文件。

TRANSACTION_NONE means that the connection does not support transactions at all, and any attempt to impose transaction semantics on that connection should fail. I can't see this ever being useful, except perhaps in cases where you're using a "fake" database, like CSV files.

另一方面，READ_UNCOMMITTED 意味着连接正在使用事务，并且将能够从其他连接的未提交事务读取数据。

READ_UNCOMMITTED, on the other hand, means that the connection is using transactions, and will be able to read data from other connections' uncommitted transactions. As @Pax said, this should be used with extreme caution.

请注意 setTransactionIsolation 方法：

Note also the setTransactionIsolation method:

请注意，不能使用 Connection.TRANSACTION_NONE ，因为它指定不支持事务。

Note that Connection.TRANSACTION_NONE cannot be used because it specifies that transactions are not supported.

所以你不能强制连接使用 TRANSACTION_NONE - 连接支持事务或它不

So you cannot force a connection to use TRANSACTION_NONE - the connection either supports transactions or it doesn't, and if it doesn't you can't mess with this method.

READ_UNCOMMITTED 仍然意味着你在交易中。您仍然会得到原子写入，并且其他事务仍然与您的写入隔离。然而，你的交易不是孤立于其他人的。 TRANSACTION_NONE 是一个免费的所有 - 没有人从任何隔离。

READ_UNCOMMITTED still means you're in a transaction. You still get atomic writes, and other transactions are still isolated from your writes. However, your transaction is not isolated from other peoples'. TRANSACTION_NONE is a free for all - no one gets isolation from anything.

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