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no. of buffers? [message #187625]

Mon, 14 August 2006 13:55

Yasir Hashmi
Messages: 304
Registered: April 2006

Senior Member

Hey all,

What determines the number of buffers that DBWn should write to datafiles?

Thanks and Regards
Yasir Hashmi

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Re: no. of buffers? [message #187629 is a reply to message #187625]

Mon, 14 August 2006 14:07

Frank Naude
Messages: 4596
Registered: April 1998

Senior Member

Eventually DBWn should write ALL modified blocks back to the data files. You don't want to lose any data, or do you?

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Re: no. of buffers? [message #187632 is a reply to message #187625]

Mon, 14 August 2006 14:13

Yasir Hashmi
Messages: 304
Registered: April 2006

Senior Member

Thanks for replyng.
By default it writes all the dirty buffers to disks.
What if we want to set some limits?

Thanks and Regards
Yasir Hashmi

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Re: no. of buffers? [message #187702 is a reply to message #187632]

Tue, 15 August 2006 01:05

Frank Naude
Messages: 4596
Registered: April 1998

Senior Member

Look at the following parameters: log_checkpoint_interval and log_checkpoint_timeout

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Re: no. of buffers? [message #187786 is a reply to message #187625]

Tue, 15 August 2006 11:09

Yasir Hashmi
Messages: 304
Registered: April 2006

Senior Member

But isn't the redo log files responsble for prevention of data loss.
LGWR writes before DBWn.

Thanks and Regards
Yasir Hashmi

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Re: no. of buffers? [message #187801 is a reply to message #187786]

Tue, 15 August 2006 13:19

Frank Naude
Messages: 4596
Registered: April 1998

Senior Member

Yes it is. However, like I've said, eventually the data must be written to the data files as well.

Oracle writes to the redo log file before a COMMIT can return to the user. In contrast, the database writer is lazy - it updates the data files in the background during checkpoint operations.

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