Re: max_commit_propagation_delay

Jonathan,

Would you recommend setting max_commit_propagation_delay to 0 in 9i2RAC ? I am considering that for my 2-node instance.

Hemant

At 10:04 AM 26-03-03 -0800, you wrote:

>It looks to me as if you've worked out exactly
>what the parameter does already.
>
>Under OPS, (and RAC) each instance has its own
>SCN range, and the ranges are not re-synchronised
>in real time (in general). SCNs are resynchronised
>by piggybacking when messages pass from instance to
>instance. However, the max_commit_propagation_delay
>sets an 'idle time' in hundredths of a second to limit
>the possible resynch delay. If no convenient message
>has passed between instances for that period of time
>then an explicit SCN message is sent.
>
>Consequently it is possible (in fact very easy) to produce
>the following effect:
> Instance A at time t0
> insert row XYZ
> commit;
>
> instance B at time t0 + delta
> select row XYZ
> no rows returned.
>
>It should also be possible to produce the effect:
> instance A at time t0
> select 10,000 rows from table T1
> fetch first 100 rows
> fetch next 100 rows
> fetch next 100 rows
>
> instance B at time t0 + delta
> insert into t1 values (XYZ)
> commit;
>
> instance A at time t0 + a bigger delta
> fetch next 100 rows - including (XYZ)
>
>To date I haven't managed to make this second
>anomaly appear on 9.2 RAC, though - but I'm still
>trying.
>
>
>If you set the max_commit_propagation_delay to zero,
>then neither of these anomalies should be possible as
>there will be no delay in propagating SCNs - but the overhead
>is likely to be significant as it probably entails a synchronous
>message to be sent through GES (or LCK0 as it would be
>in 8.0.6)
>
>
>Note for 9i / RAC - (and possibly earlier) although there
>is a default 7 seconds set for this parameter, the effect
>of the running checkpoint mechanism seems to force
>a cross-instance message every three seconds anyway.
>
>
>
>
>Regards
>
>Jonathan Lewis
>http://www.jlcomp.demon.co.uk
>
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>----- Original Message -----
>To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com>
>Sent: 26 March 2003 14:34
>
>
> > OPS 8.0.6.3 on Sun Nodes. We have this currently set to 0, and
>Oracle has
> > recommended that we leave it at the default of 700, while making a
>general
> > recommendation to improve the performance of this database. But from
>what I
> > have gathered so far from Metalink, this would not suit us, since,
> > transactions would immediately need to see the data on the other
>node. Is
> > my assumption correct? Can someone throw more light on this
>parameter? Any
> > good links? Strangely, I did not find any reference at
>www.ixora.com.au,
> > though that site has never dissappointed me.
> >
> > Thanks
> > Raj
> >
>
>
>--
>Please see the official ORACLE-L FAQ: http://www.orafaq.net
>--
>Author: Jonathan Lewis
> INET: jonathan_at_jlcomp.demon.co.uk
>
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Hemant K Chitale
My personal web site is : http://hkchital.tripod.com

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  INET: hkchital_at_singnet.com.sg

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