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FILTER FACTOR


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Ananya

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Joined: 26 Feb 2004
Posts: 19
Location: Chennai

PostPosted: Fri Feb 27, 2004 4:04 pm
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Dear All,

1. What is a FILTER Factor?

2. What is the Functionality of this Filter Factor?

Pls. Help me.

Cheers

-Ananya
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anuradha

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Joined: 06 Jan 2004
Posts: 247
Location: Hyderabad

PostPosted: Fri Feb 27, 2004 5:42 pm
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hi ananya,

Filter factors affect the choice of access paths by estimating the number of rows qualified by a set of predicates.

These estimates the proportion of rows in a table for which the predicate
is true. Those rows are said to qualify by that predicate.

suppose for table EMP consider in the NAME COLUMN there are 4 distinct names say A B C and D.so now 1/4 th of the rows have value A in NAME column.Then the predicate NAME='A' has the filter factor 0.25 for table EMP.

Statistics generated by runstats helps in calculating FILTER FACTOR.

hope this give u some idea atleast.

THANKS AND REGARDS
ANU
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Ananya

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Joined: 26 Feb 2004
Posts: 19
Location: Chennai

PostPosted: Sat Feb 28, 2004 1:06 pm
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Dear Anu,

Thanks for the Help. Your comprehension is beyond my understanding. icon_cry.gif

But one thing I understood is, a Filter Factor is 1 / No.Of. Distinct rows of a Column.

Can you please put this a little more simpler of why a Filter Factor is applied?


Cheers
-Ananya
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anuradha

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Joined: 06 Jan 2004
Posts: 247
Location: Hyderabad

PostPosted: Mon Mar 01, 2004 10:14 pm
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hi ananya,


As i said earlier filter factor affect the choice of access paths.The optimizer uses filter factor(not only this.still many factors) to choose the best method for accessing data.

There will be two phases in processing a query. compile phase(also known as PREPARE or BIND phase), and the EXECUTE phase. In the COMPILE phase, the DBMS chooses an optimal Access Path (or access strategy) to compute the result of the query. Once chosen, the access path is stored in an object known as an Access Plan that can be retrieved for later use. The Access Plan is then executed in the EXECUTE phase to produce the result for returning to the application. Typically, a query is associated with a single access plan. Access Plan can be shared and reuse for multiple execute requests by multiple applications executing the same query.

DBMSs collect and maintain a multitude of statistical information about the data they manage in order to optimize access paths for queries on these data. Such statistics include the distribution of the data and frequent occurring values in the data.

One important usage of these statistics is in the computing Filter Factor (how many rows in the table or relation will qualify a given predicate) of various predicates in queries. The Filter Factor of predicates is basis for DBMSs to select optimal access paths for queries.


hope this time u should get a clear idea. icon_idea.gif right!!!!!!!!!.

OK HAVE A NICE DAY ANANYA.


Thanks and regards
ANU icon_lol.gif
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mdtendulkar

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Joined: 29 Jul 2003
Posts: 237
Location: USA

PostPosted: Wed Mar 03, 2004 1:26 pm
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Hello Ananya,

Check out the following links for more information
Code:

http://vsis-www.informatik.uni-hamburg.de/teaching/ws-03.04/edbec/db2library/db2t0e80.pdf

https://aurora.vcu.edu/db2help/db2t0/db2t0.htm

http://www.frc.utn.edu.ar/campus/ibm/pdfs/sg242213.pdf

http://www.dbis.informatik.uni-frankfurt.de/~schommer/wise02/practical/exerc/DB2Glossary.pdf


Hope this helps,

Regards
Mayuresh Tendulkar
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