How do I calculate disk usage for a table

Question

Is there a formula or equation that I can use to calculate disk usage (in MB) for a table?
I would like to foind out what's the best option for initial storage space and monthly growth.

Answer 1

Hi,
We will discuss this by taking a simple example:
SQL>Create table T_REGISTRATION (Name varchar2 (100),
Fathers_Name varchar2 (100),
Age number(5),
Sex char (1),
Data_of_Birth Date)
storage (initial 40k next 40k minextents 5)
Tablespace TBS1;
Table created.
SQL> insert into T_REGISTRATION values ('Name_1','Name_1_Father',40,'M','24-FEB-66');
1 row created.
SQL> Commit;
Commit complete
SQL> analyze table T_REGISTRATION compute statistics;
Table analyzed.
SQL> compute sum of blocks on report
SQL> break on report
SQL> select extent_id, bytes, blocks
from user_extents
where segment_name = 'T_REGISTRATION'
and segment_type = 'TABLE';
EXTENT_ID BYTES BLOCKS
0 65536 8
1 65536 8
2 65536 8
3 65536 8
Sum 32
SQL> clear breaks
SQL> select blocks, empty_blocks,
avg_space, num_freelist_blocks
from user_tables
where table_name = 'T_REGISTRATION';
BLOCKS EMPTY_BLOCKS AVG_SPACE NUM_FREELIST_BLOCKS
5 27 8064 0
From above:-
1.     We have 32(Sum) blocks allocated to the table
2.     27 blocks are totally empty
3.     5 blocks contains data(BLOCKS+EMPTY_BLOCKS = SUM i.e 5+27=32)
4.     We have an average of about 8064 bytes = 7.8 free on each block used (8064/1024=7.8K From above AVG_SPACE value).
Therefore our table
1.     Consumes 5 blocks
2.     In this 5blocks * 8k blocksize - 5 blocks * 7.8K free = 1k is used for inserted data.
Source for this example :- asktom.oracle.com
Thanks,
Sankar