读一致性(Read consistency):用于多用户并发的情况下,一个用户修改了若干条记录,但没有执行commit操作,其他用户在查询时,看到的仍旧是没有修改的数据。
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作为数据库内部的逻辑时钟,数据库事务依SCN而排序,Oracle也根据SCN来实现一致性读(Read Consistency)等首要数据库功能。别的对于分布式事务(Distributed Transactions),SCN也极为首要,这里不做更多介绍。
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这一版增加了读取一致性(Read Consistency),确保用户在查询期间看到一致的数据。也就是说,当一个会话正在修改数据时,其他的会话将看不到该会话未提交的修改。
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Monotonic read consistency 单调读一致性 ; 一个用户一旦读到某个值
Transaction-Level Read Consistency 一致性
statement-level read consistency 语句级读一致性
Read-consistency error 读的一致性错误
Write Follows Read Consistency 写读一致性
Read-your-writes consistency 一致性 ; 读己所写一致性
Read Your Writes Consistency 读写一致性
Read Write Consistency 读写一致性
Oracle supports a mechanism called Multi-Version Read Consistency which is implemented by undo data in the undo segments.
Oracle支持一种称为Multi - Version Read Consistency的机制,这是用undo段中的undo数据实现的。
If the business requires greater availability but read consistency is not a premium, then an asynchronous option may be a more cost-effective approach.
如果业务要求更高的可用性,并且读一致性不是很重要,那么选择异步可能是更经济的方法。
That's also a costly option, however, because every time you iterate across the contents of the collection, you have to synchronize all operations, including read and write, to ensure consistency.
然而,这也是一个成本较高的选择,因为每当您跨集合内容进行迭代时,您就不得不同步所有操作,包括读和写,以此保证一致性。
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