Re: Log Switches in RAC

From: Yong Huang <>
Date: Wed, 11 Nov 2009 15:03:42 -0800 (PST)
Message-ID: <>

> If any of the thread is not archived for longer duration
> and if the critical changes are recorded in that thread,
> you may not be able recover the database as the physiological
> logging requires all the changes from ALL the thread to make
> the recovery complete

There is (or was?) the concept "force archive SCN". I know of two sources where this is talked about. Rama Velpuri's "Oracle(8) Backup and Recovery Handbook" and Lawrence To's "Archiving Tips and Hints". The latter can be found at

"Threads are kept relatively current by forcing log switches or kicking idle instances to archive. For an open and enabled thread, a lock is used to kick an idle instance. For a closed and enabled thread, the ARCH process for an active instance will log switch and archive the closed
thread. A force archive SCN is maintained in the control file to implement this feature.

"OPS: The ARCH process scans the archive link list found in the control file and archives all inactive redo logs whose SCN is less than the force archive SCN. Oracle strives to archive any log that contain less than or equal to the force archive SCN. Generally, the log with the lowest SCN is archived first."

Yong Huang       

Received on Wed Nov 11 2009 - 17:03:42 CST

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