Re: Clustering factor smaller than table blocks.


One possibility relates to ASSM - you can have
blocks below the highwater mark that are not
yet formatted. I'd have to check, but I don't think
they get recorded as EMPTY_BLOCKS.

The rather more surprising thing about your example
is that you have done a compute, so the results should
be accurate, but you have  36,364 rows in the table
and only 36,112 entries in what we guess is the primary
key index.  Do you have a corrupt index perhaps ?

Regards

Jonathan Lewis
http://www.oracle.com/technology/community/oracle_ace/ace1.html#lewis

The Co-operative Oracle Users' FAQ
http://www.jlcomp.demon.co.uk/faq/ind_faq.html

Cost Based Oracle: Fundamentals
http://www.jlcomp.demon.co.uk/cbo_book/ind_book.html


----- Original Message ----- From: "Polarski, Bernard" <Bernard.Polarski@xxxxxxxxxxxxxx>
To: <oracle-l@xxxxxxxxxxxxx>
Sent: Wednesday, September 27, 2006 9:47 AM
Subject: Clustering factor smaller than table blocks.


I have a table with 368 blocks, no free blocks, and the clustering
factor of the primary key is 345. how is it possible?

I thought that CF will give you the amount of table blocks that an index
will need to access for a given rowset. Something like
smallest( table blocks, ceil( (CF/tot table rows)*rowset/avg rows per
block)) (real formula must be much complicated.

However if I have an avg ro

Here are the brute facts:

select EMPTY_BLOCKS,AVG_SPACE_FREELIST_BLOCKS ,NUM_FREELIST_BLOCKS
         from dba_tables where table_name = 'CUSTOMERS' and owner =
'SOE' ;

EMPTY_BLOCKS AVG_SPACE_FREELIST_BLOCKS NUM_FREELIST_BLOCKS
------------ ------------------------- -------------------
          0                         0                   0


The table was analysed with dbms_stat, percent  = 100:

exec dbms_stats.gather_table_stats( ownname=>'SOE', tabname=>
'CUSTOMERS', Degree=> 4, estimate_percent=> 100, granularity=>'ALL',
cascade=>TRUE, stattab=>'sm_stattab', statid=>'CUSTOMERS09270906',
statown=>'SOE')


Table name Owner NUM_ROWS BLOCKS
Size (m) LAST_ANALYSED
------------------------------ ---------------- ---------- ----------
-------- ------------------- CUSTOMERS SOE 36364 368
3 09/27/2006 08:39:50


But still the clust factor reported by dba_indexes for CUSTOMERS_PK is
inferiors to CUSTOMERS block count.


Table                Index                            Column
Clust   Distinct
Name                 Name                           U Name
Factor       Keys   NUM_ROWS
-------------------- ------------------------------ -
-------------------- ---------- ---------- ----------
CUSTOMERS            CUSTOMERS_PK                   U CUSTOMER_ID
345      36112      36112

This is oracle 10.1.0.4


B. Polarski




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