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Properly sizing the extents

We have a Oracle database(7.3.2.1) with db_block_size 8k on Sun UltraSparc machine(Solaris Ver 2.6).
I created a tablepsace with the default storage parameter 'initial extent' as 64K(ie 8 db blocks). But the objects created in the tablespace takes up 80K(ie 10db blocks) for its initial extent. I created the object in the tablespace by explicitly specifying the storage parameter for the object.(with initial extent size as 64K). This also creates extents with 80K.
How to prevent the Oracle from doing this rounding and get the correct extent size which I need?

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xiaodong

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srikumar_p

ASKER

Thanks xiaodong for the answer.
I don't mind wasting 16K. But the thing is I have set the db_multiblock_read_count parameter as 8. That means Oracle will read 64K in one read.(8*8Kb) If my extent size is 80K this will result in 2 reads(during full table scans)- one for the first 64K and the second one for remaining 16K. These reads can't span extents. So this will reduce the preformance as two reads are required for an extent. Is it advisable to set the db_multiblock_read_count to 10?

Then, I don't think the smallest increment is 5 DB blocks. Because I am able to create the extent with 4 DB blocks(ie 32KB in my database). But any thing above 4 it rounds to 10.

xiaodong

db_multiblock_read_count really depends on the file I/O on the O/S. I believe most UNIX systems allows at most 64K read in one I/O operation. So this parameter should always set to take advantage of the O/S capability. In your case, 8 is fine. If you set it to 10, you will see no gains at all.
Secondly, if you can show me any proof(such as select from dba_segments) that you are able to create an extent of 32K in a database using block size of 8K, I will be very surprised.

srikumar_p

ASKER

Hi xiaodong,
Thanks for your suggestions.
For the 32K extent using 8K db block size - you can see the commands I cut and pasted from
sql*plus
SQL> create table emp (empno integer, empname varchar2(20))
2 storage (initial 32k minextents 1);

Table created.

SQL> select * from user_extents where segment_name = 'EMP';

SEGMENT_NAME SEGMENT_TYPE
--------------------------------------------------------------------------------- -----------------
TABLESPACE_NAME EXTENT_ID BYTES BLOCKS
------------------------------ --------- --------- ---------
EMP TABLE
DATA_TBSP 0 32768 4

SQL>

and the db_block_size is 8K- trust me :-)

By the way, can I know more about you? Where are you working? What environment etc. etc.
My mail id is kumarp@wipsys.soft.net. You can mail to me directly rather than through the web.

The web is very slow during our office hours. It is World Wide Wait(www) really.

Thanks again.