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关于rac环境下flush redolog情况

1^#

发表于 2012-4-19 21:00:33 | 查看: 5955| 回复: 6

当发生global cache current blocks的传输时，会发生flush redo log,这点比较好理解！但是，为什么构造cr块，发生global cache cr blocks也会触发flush redo log呢？

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Maclean Liu(刘相兵

2^#

发表于 2012-4-19 21:44:05

A log flush for a cr block transfer is required when a cr buffer is cloned from a current buffer which has redo
pending. A high percentage is indicative of hot blocks with frequent read after write access.

consistent read 中 cr block 可能来源于 current block 的 clone ，而current block 的相关redo 可能会未写出，需要这些 redo flush后 cr block才能被send 。

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Maclean Liu(刘相兵

3^#

发表于 2012-4-19 21:53:26

PS:

可以通过设置_cr_server_log_flush to false(LMS are/is waiting for LGWR to flush the pending redo during CR fabrication. Without going too much in to details, you can turn off the behaviour by setting _cr_server_log_flush to false.) 来禁止cr server flush redo log，但是该参数对于current block的flush time无效，也强烈不推荐使用。

_cr_server_log_flush TRUE TRUE if TRUE, flush redo log before serving a CR buffer

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gdpr-dba

4^#

发表于 2012-4-19 22:05:23

原帖由 maclean 于 2012-4-19 21:44 发表
A log flush for a cr block transfer is required when a cr buffer is cloned from a current buffer which has redo
pending. A high percentage is indicative of hot blocks with frequent read after write ac ...