Re: Optimizer issue - cost of full table scans

From: Niall Litchfield <>
Date: Mon, 13 Sep 2010 18:57:41 +0100
Message-ID: <>

Hi Greg,
I meant to ask previously, but didn't. Are there any changes to system stat calculation for exadata? You earlier talked about getting stats representative, I wonder (in the absence of an exadata play box), how representative the system stat IO and CPU costing is in this environment?

On 13 Sep 2010 17:49, "Greg Rahn" <> wrote:


This is actually a poor recommendation. Using a "estimate_percent=>null" will be very very costly and since the OP is on 11g (11.2 in fact as he is on Exadata V2), the default value for estimate_percent of dbms_stats.auto_sample_size is much faster and usually within
>99% accuracy of a 100% sample.

More details on why:

On Mon, Sep 13, 2010 at 6:14 AM, Pavel Ermakov <> wrote:
> Hi
> Try to ga...

Greg Rahn

Received on Mon Sep 13 2010 - 12:57:41 CDT

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