Re: Varying plans on different nodes

  • From: "Stefan Knecht" <knecht.stefan@xxxxxxxxx>
  • To: fairlie_r@xxxxxxxxx
  • Date: Thu, 7 Jun 2007 10:52:15 +0200

Hi fairlie

Do you have system stats in place ?

if this is 10g -- you didn't mention;  isn't it possible that upon instance
startup, system stats are gathered with noworkload per default at instance
startup. Therefore, when instance 1 starts, it gets a set of "default"
system stats, and perhaps it has them cached somewhere in memory ? And when
instance 2 starts up, it gets a different set and uses those ?

Just thinking out loud here.



On 6/7/07, fairlie rego <fairlie_r@xxxxxxxxx> wrote:

Thanks Greg,

But doesn't gather_system_stats populate sys.aux_stats$ and hence is
consistent throughout the cluster?


*Greg Rahn <greg@xxxxxxxxxxxxxxxxxx>* wrote:

The object stats would be the same, but it is possible for the system
stats to be different. Have you validated they are consistent across
nodes? Perhaps it would be best to snag the system stats that produce
the good plan and import them to the other nodes.

On 6/6/07, fairlie rego wrote:
> Hi all,
> I have a query which has a good plan on one node (node 3) and a bad plan
> (node 1) caused by a Merge Join Cartesian on another.
> Bind variable peeking is disabled and dynamic sampling is disabled for
> query. There is no difference in v$sql_optimizer_env for the query
> the 2 nodes.
> In the 10053 output I see a difference in RSC_IO for fast full scan of
> indexes which I thought was based on the leaf blocks and blevel. Given
> the stats across nodes are the same how can this happen?. If this is due
> varying load because of workarea_size_policy how do we protect
> I can send the 10053 outputs but here is one snippet
> Node 3
> ======
> Access Path: index (index-ffs)
> rsc_cpu: 875652262 rsc_io: 8606
> ix_sel: 0.0000e+00 ix_sel_with_filters: 1.0000e+00
> Node 1
> ======
> Access Path: index (index-ffs)
> rsc_cpu: 875652262 rsc_io: 26521
> ix_sel: 0.0000e+00 ix_sel_with_filters: 1.0000e+00
> Thanks
> Fairlie


Greg Rahn

  *Fairlie Rego
*Senior Oracle Consultant
M: +61 402 792 405

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Stefan P Knecht
Infrastructure Managed Services

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