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Read Committed Isolation (327)

原创 ERP 作者:tsinglee 时间:2007-12-08 13:42:45 0 删除 编辑

For many applications, read committed is the most appropriate isolation level. Read
committed isolation can provide considerably more concurrency with a somewhat
increased risk of inconsistent results due to phantoms and non-repeatable reads for
some transactions.

Many high-performance environments with high transaction arrival rates require more
throughput and faster response times than can be achieved with serializable isolation.
Other environments that supports users with a very low transaction arrival rate also
face very low risk of incorrect results due to phantoms and nonrepeatable reads. Read
committed isolation is suitable for both of these environments.

Oracle read committed isolation provides transaction set consistency for every query.
That is, every query sees data in a consistent state. Therefore, read committed isolation
will suffice for many applications that might require a higher degree of isolation if run
on other database management systems that do not use multiversion concurrency

Read committed isolation mode does not require application logic to trap the Cannot
serialize access error and loop back to restart a transaction. In most applications,
few transactions have a functional need to issue the same query twice, so for many
applications protection against phantoms and non-repeatable reads is not important.

Therefore many developers choose read committed to avoid the need to write such
error checking and retry code in each transaction.

幻象读取的风险也较低. 以上两种系统均适合采用已提交读取隔离


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