有个关于cache的问题，请指教

Cluster

If it's say "For example" every 3 Sec. maybe o.k. Otherwise totally misleading!
Why you need all that parameters ? What all control variables for?
Do you take that as true?
Sorry, I don't know where can sent the 悄悄话. how about just post your problems here if not the 悄悄话?

snowhite2000

I do like to post my questions and all my experience here.  I just wish I can have some good resourses when I really need help sometime. Maybe  I asked too much.

Here is some information about LGWR for your refenerce:

From Oracle training Book, enterprise DBA Part 1B: backup and Recovery Workshop, Page 2-15:

Function of the LGWR Background Process
The log writer(LAWR) writes redo entries to the redo log files that have been copied into redo log buffer since the last time it wrote to the redo log files:

1. when the redo log buffer is one-third full
2. when a timeout occures (every three seconds)
3. before DBWn writes modified blocks in the database buffer cache to the data files
4. When a transaction commits
5. As long as the database, if obliged to archive the redo log files, did archive the redo log to be overwritten again

And about DBW0, on the training book:
DBW0 write when:
1.The number of dirty buffers reaches a threshold value (snowhite:  on DIRTY LIST)
2. a sprocess scans a specified number of blocks when scanning for free buffers and cannot find any (snonwhite:  on LRU)
3. A timeout occurs (every three sconds)
4. a checkpoint occurs

I also remember on another Oracle training class - Oracle internal, Oracle explains the parameters controling the values of DIRTY LIST and LRU.  I am sorry I don't have that material now.

ttdb

what snowhite post is  clear enough .

我讨厌  这样的词 “请指教（低手不宜） ”

降龙十八掌

闻过即改

其实我也是不得已才出此下策，否则这个问题也不会有人回答，不过，这个问题确实有质量。希望有更多人深入探讨一下Oracle的内部机制，这样更有利于理解Oracle的运作。

TOM

[1、如果Dirty list超过1/3满了，DBWR自动写dirty buffer到文件也会出发LGWR吗？
2、如果Buffer Cache在3秒后自动进行一次DBWR，那也会触发LGWR吗？
[/B][/QUOTE]
lgwr进程在启动事例时自动启动。
lgwr进行写操作的情况在：
1、用户进程提交一个事物（commit）；
2、日志缓冲区达到1/3范围，DBWR对一个检查点需要清除缓冲快；
3、出现超时（3秒钟未活动，则进行一次写操作）；

machao

我上星期在metalink上无意中找到这个文件,觉得对你有帮助.
它详细的解释了dbwr和cache manager的概念问题.

我在这里顺便问一个问题,我们如何在metalink上找到类似的文档?
比如说lgwr,checkpoint的更深入讨论.我知道很多人都不是很清楚,
我就是其中一个.
假如有100个这样的文档.我们便好使了.

Cluster

machao:  Thank you for the paper attaching, which help many of us to clear out the misleading stuff  from Oracle Education.
How to use Metalink, you can find out from on line help or just use KEY Words search, i.e. LGRW,
CHECKPOINT....  Most of those papers from Oracle Developer team and Oracle Support team, with much precise technical description compare to the lousy Oracle Education materials, and the best quality of papers are from Oracle COE team,  unfortunately, those papers for Oracle internal only.