About DB statistics

Hello All
can anyone tell me about this DB Statistics in Infocube manage tab.
about these push buttons
Check Statistics
Create Statistics(Btch)
Refersh Statistics
Regards
balaji

Most major databases today utilize what is know as a "Cost Based Optimizer" or CBO.  The CBO evaluates the SQL stmt the BW query generates and makes decisions about what the best way to run the query might be - what order it should read the tables in, should it use an index on the table, or scan the entire table, etc.
There quite literally, might be hundreds or even thousands of combinations and permutations of how the database might run your query.  The purpose of the CBO is to make a decision as to what it thinks is approach that will be the most efficient, which usually translates to mean, the least amount of disk IO.
In order for the CBO to make informed decisions, it wants to know things like:
- how many rows are are in each table that is referenced in the query.
- what indices exist on these tables.
- how many distinct values for a column exist.
It gets more complicated than this, but this give you a good idea I think.
All this statistical information about you tables is stored in system tables, and the CBO looks at this data to make it's decisions about which plan will be the best.
The information in these system tables can become out of date if it is not refreshed periodically.  It is not hard to imagine that the CBO could make some bad decisions if it thought there were 10,00 rows in a particular table, when in fact, there was 100,000,000, or if it thought there were 50 different values for Business Area, but in fact, there are 500.
So - you can see I think, that the more accurate the statistics, the better the odds that the CBO makes the best decision about how to run the qurey (known as the Execution Plan or Explain Plan). Old or missing statistics can lead to very bad choices by the CBO, resulting in orders of magnitude in worse performance in some cases.  
Finally -
The DB Statistics options for the InfoCube allow you to collect current DB statistics about the tables associated with the InfoCube.
Using the automation settings or Process Chains, the collection of statistics can be automated as part of the nightly loading of each InfoProvider.  There are other options that the DBAs in your shop might have implemented to keep statistics updated, so before you go and make changes, you should consult with them.
Pizzaman

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    RealBlackStuff
    Mt. Cobb, PA USA
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    Message Edited by andyP on 11-30-2007 04:33 PM
    Message Edited by andyP on 11-30-2007 04:33 PM
    Andy  ______________________________________
    Please remember to come back and mark the post that you feel solved your question as the solution, it earns the member + points
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