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Message Posted: Tue, 24 Jan 2012 @ 14:52:00 GMT


     
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Subj:   Why does size of table increase in multiples of 512 bytes
 
From:   sukul mahadik

Hi all

While testing some issue i came across this phenomenon.

I have created a table with one column of CHAR(20). When i insert a row in this table , the size of the table increases by 512 bytes and not 20 bytes. I believe it should increase by 20 bytes as i am inserting data only to CHAR(20) field.

I am not able to understand , why the size has been increasing in multiple of 512 bytes and not 20 bytes.

Following is what i had ran:

     CREATE TABLE RESTORE_TABLES.TESTTABLE, NO FALLBACK (
     FIELD1 CHAR(20)
     );

     /* CREATED A TABLE WITH ONLY 1 COLUMN fo CHAR(20)*/


     SELECT SUM(CurrentPerm)
        FROM DBC.ALLSPACE
        WHERE DatabaseName='RESTORE_TABLES' AND     TableName='TESTTABLE'

Result is 196608.00 BYTES.

     INSERT INTO RESTORE_TABLES.TESTTABLE VALUES('ABC')
     SELECT SUM(CurrentPerm)
        FROM DBC.ALLSPACE
        WHERE DatabaseName='RESTORE_TABLES' AND TableName='TESTTABLE'

Result is 197120.00 . Thus the increase is by 512 bytes.

     INSERT INTO RESTORE_TABLES.TESTTABLE VALUES('CDF')
     SELECT SUM(CurrentPerm)
        FROM DBC.ALLSPACE
        WHERE DatabaseName='RESTORE_TABLES' AND TableName='TESTTABLE'

Result is 197632.00 . Thus the increase is again by 512 bytes.

     INSERT INTO RESTORE_TABLES.TESTTABLE VALUES(NULL)
     SELECT SUM(CurrentPerm)
        FROM DBC.ALLSPACE
        WHERE DatabaseName='RESTORE_TABLES' AND TableName='TESTTABLE'

Result is 198144.00. For null value also increase is by 512 bytes.

Can anybody please help me understand why the size is in multiples of 512 bytes.


Thanks

Sukul



     
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