Re: Commit -> write to data file immediately???

From: Norman Dunbar <ndunbar_at_lynxfinancialsystems.co.uk>
Date: Thu, 29 Mar 2001 11:27:31 +0100
Message-ID: <F43E6BAE5BB5D411A44C00805FBE740D6DE400@apps.lynx-fsc.co.uk>

David,

when the user commits, Oracle guarantees to write the REDO information to the redo logfile. When this has been successful, the user gets the 'n records committed' message. The changed data is still held in the buffer cache but has not yet been written to disc.

Sounds bad, but because the redo log holds the details of how to rebuild that entire transaction, then it can be rolled forward in the event of a database failure with subsequent recovery. (ARCHIVE LOG mode required of course (unless the whole transaction details are still in the on-line redo logs)).

The data in the buffer cache is written to the actual datafiles at certain times when a checkpoint occurs. This is caused by a redo log switch, a timeout (every 3 seconds), when the redo log bugger becomes one third full etc.

If I've missed anything, Howard will be sure to mention it (and correct me if I got it hopelessly wrong !) :o)

Regards,
Norman.

Norman Dunbar		EMail:	NDunbar_at_LynxFinancialSystems.co.uk
Database/Unix administrator	Phone:	0113 289 6265
Lynx Financial Systems Ltd.	Fax:	0113 201 7265
			URL:	http://www.LynxFinancialSystems.com


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Received on Thu Mar 29 2001 - 04:27:31 CST