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Update Statiscts SAMPLE_ROWS

Update Statiscts SAMPLE_ROWS

2007-07-03       - By Becker, Holger

 Back
Daniel Castro wrote:

> Hi,
>
> I want to know the % of rows to be used as sample_rows for a
> table, because
> I get the following message:
>
> I  1 tables contain > 1.000.000 records but only 20.000 rows
> will be sampled
> for statistics
>       CON: NUM_TABS_FEW_SAMPLE_ROWS > 0
>       VAL: 1
>
> Is there any pattern?
> How I change this value?
>
> Best Regards,

Hi Daniel,

our recommendation is to use a sample rate of 5% for at least all tables with
more than 1000000 rows.
But from my point of view you could also use it for smaller tables as long as
the runtime of the
update statistic command doesn't influence your system to much.

You could change the sample rate with "alter table <table name> sample
<unsigned int> percent | rows".

To check the actual sample rate use "select schemaname, tablename , sample
_percent, sample_rows from tables".

Kind regards
Holger


Holger Becker
MaxDB&liveCache
SAP AG
www.sap.com
Sitz der Gesellschaft/Registered Office: Walldorf, Germany
Vorstand/SAP Executive Board: Henning Kagermann (Sprecher/CEO),  L?o Apotheker,
Werner Brandt, Claus Heinrich, Gerhard Oswald, Peter Zencke
Vorsitzender des Aufsichtsrats/Chairperson of the SAP Supervisory Board: Hasso
Plattner
Registergericht/Commercial Register Mannheim No HRB 350269

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