Re: Automatic checkpoint tuning on RAC

From: joel garry <>
Date: Wed, 1 Jul 2009 13:11:14 -0700 (PDT)
Message-ID: <>

On Jul 1, 12:19 pm, "Jonathan Lewis" <> wrote:
> "Mladen Gogala" <> wrote in message
> news:h2gbfd$3q8$
> >I recently talked about the automatic checkpoint tuning with a colleague
> > of mine and we considered setting fast_start_mttr_target to a decent non-
> > zero value like 300 on a RAC database. I am aware of the recommendation
> > not to set it and the argument for that recommendation is the fact that
> > another RAC instance will do a recovery, if an instance fails.
> Have you got a reference for the recommendation to not set it ?

See "Best Practices for Optimizing Availability During Unplanned Outages Using Oracle Clusterware and Oracle Real Application Clusters" section "Understand the Instance Recovery Target and Optimize if Required" which is referred to in

"In a RAC 10g Release 2 Patchset 2 environment (, the best practice is to use the _FAST_START_INSTANCE_RECOVERY_TARGET parameter instead of the FAST_START_MTTR_TARGET parameter. The _FAST_START_INSTANCE_RECOVERY_TARGET parameter represents the number of seconds that it will take a surviving instance to recover the redo thread of a failed instance. This includes the first pass redo scan, recovery claiming, and the second pass redo application.

So, an important distinction is the fact that FAST_START_MTTR_TARGET bounds the total time for startup, mount, crash recovery, and open whereas
_FAST_START_INSTANCE_RECOVERY_TARGET bounds only instance recovery. Another important point is that _FAST_START_INSTANCE_RECOVERY_TARGET is based on the assumption that only one instance has failed. It is not correct to expect
_FAST_START_INSTANCE_RECOVERY_TARGET to properly bound instance recovery when multiple instances have failed"

> It seems to be fairly irrelevant to suggest that it's not needed because
> "another RAC instance will do a recovery" - the fast_start_mttr_target
> would surely affect the time it takes that instance to do the recovery.

This is all academic to me. But I find the recommendation of an underscore parameter from an indirect doc reference interesting.


-- is bogus.
Received on Wed Jul 01 2009 - 15:11:14 CDT

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