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Re: DR Failover data loss

From: Carel-Jan Engel <>
Date: Fri, 24 Jun 2005 11:41:56 +0200
Message-Id: <>

Hi Visal,

Please see my comments inline.

On Fri, 2005-06-24 at 09:47, vishal shah wrote:

> Hi,
> We have a 2 node RAC database with a physical standby at a remote
> location in MAXIMUM PERFORMANCE mode.

Version, OS?

> This ensures that the primary
> database works smoothly in case there are any issues with the DR site.

What is smoothly? If the standby fails, even MAX. AVAILABILITY will let the primary continue after the (configurable timeout) passed.

> Opting this also means that there might be data loss in case of the
> primary site going down. The data loss will be for all the archive
> logs that are not transported and applied at the standby database.

Max. performance is not restricted to redo shipping by ARCH. It can also be implemented with LGWR redo shipping in place, in ASYNC mode. In that case you might have some transactions in the online redo replicated to the other end as well. If you're lucky, all transactions might be there.

> That might be a few minutes in case of peak time and a few hours in
> case there is no load. Is there some way to find out how much will be
> the data loss time? 10 minutes / 20 minutes?

Monitor V$ARCHIVED_LOG (for remote destinations) and V$ARCHIVE_GAP for the actual GAP. Maybe you can predict (by analyzing the historicy of your monitoring) with some accuracy how much data loss you risk at certain times of the day

> Also is there some way to
> ensure that archive logs gets generated every N minutes whether the
> log file is full or not? I've looked at FAST_MTTR_TARGET but it does
> not help. It is set to 300 but there are occurances wherein the log
> file has not been generated for 4-5 hours in our case.

Look at parameter ARCHIVE_LAG_TARGET.

> Thanks,
> --

Best regards, Carel-Jan

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Received on Fri Jun 24 2005 - 05:47:11 CDT

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