热备份与RMAN备份中split block的处理

最新推荐文章于 2024-06-18 02:21:43 发布

转载最新推荐文章于 2024-06-18 02:21:43 发布 · 120 阅读

本文详细介绍了在Oracle数据库中，分裂块（split block）这一特定类型的介质损坏现象及其处理方法。在热备份过程中，为避免分裂块导致的数据损坏，需要将表空间置于备份模式。而使用RMAN进行备份时，服务器进程会确保读取到一致性的数据块版本。

fractured block (split block 定义)
A type of media corruption that can occur when database writer is writing a block at the same time an operating system utility is reading the block for backup. The block that the operating system reads can be split, that is, the top of the block is written at one point in time while the bottom of the block is written at another point in time. If you restore a file containing a fractured block and Oracle reads the block, then the block is considered a corrupt block.

热备份中split block的处理：
The potential for fractured blocks necessitates putting tablespaces in backup mode before user-managed online backups. A database in backup mode writes whole Oracle data blocks to the redo log, so that if a block is split during the backup, you can repair it by using redo.

RMAN 中split block的处理：

Recovery Manager does not experience this problem because the server process performing the backup or copy reads each block to determine whether it is split and re-reads the block until it gets a consistent version.

由于热备份是在begin backup 之后的OS 上的cp命令，所以在遭遇split block的时候，只能将整个block 写入redo log . 以便后面能通过redo 来修复它(split block) 。

RMAN备份处理split block与热备份不一样，它不存在这样的问题，是因为它在执行备份每个数据块的时候会判断这个数据块是否是split 的，如果是它会重新读这个数据块直到得到一个consistent version .

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