From: John Hurley <>
Date: Tue, 29 Sep 2009 12:41:48 -0700 (PDT)
Message-ID: <>

On Sep 29, 10:24 am, The Magnet <> wrote:


> Decent page to read.  The kind of documentation which will need
> several passes to completely understand.
> One question is that each table may have different needs.  In a case
> like this, I have the option of going through each table, or, using
> manual or dynamic sampling.  Though it says Oracle chooses a good
> value for the sample, it should probably be based on something else.
> One thing regarding skewed data that I may not understand the
> concept.  Say I have a table which has a customer ID, which is
> unique.  I assume no reason to gather stats as the number is unique
> with an index, is that right.  However, say there is another column in
> which 75% of the data contains 1 value.  Then, does the table meet the
> criteria for gathering stats?  Should I compute table stats on this?
> Sorry for all the questions, just my misguided understanding of the
> details,
> Thanks

You have to step back and go very carefully with test cases and build your knowledge.

Start by creating a simple table with no indexes and load a few rows in there. Do a dbms_stats.gather_table_stats and find out what gets populated where ( dba_tables for example ) ... do a drop_table_stats and see what has changed ...

Maybe you need to start with Tom Kyte's book "Expert Oracle Database Architecture" along with Jonathan Lewis's book Cost-Based Oracle fundamentals.

It is going to take a bunch of time and effort for you to start to understand how deep and complicated this whole area is ... if you are motivated enough to do the homework. Received on Tue Sep 29 2009 - 14:41:48 CDT

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