Calculating the Size(KB) in the explain plan....

Question

Hi
I executed a sql statement in SQL*PLUS and having enabled the tracing in OEM , among others , I read the Size in KiloBytes which the 'TABLE ACCESS FULL' segment of the explain plan returned.....
This number is 5.998,193KB
I used the vsize built-in function in order to get the total number in bytes of the physical representation of all the rows (about 53500) ....
So , I wrote :
select nvl(sum(vsize(farmak_code)),0)+nvl(sum(vsize(emp_name)),0)+nvl(sum(vsize(category)),0)+ .....+.....
from mitroo_farmakou
The result was 5794544 in bytes which is close to 5.998,193KB.
My question is :
The computation of the bytes in the explain plan (TABLE ACCESS FULL segment) is done by adding the vsize of all columns....????
Does anybody Knows...????
Thanks , a lot
Simon

Answer 1

I doubt it. For a large table that would be an incredibly expensive calculation.
I suspect that it is something closer to:
SQL> SELECT * FROM incident;
Execution Plan
   0      SELECT STATEMENT Optimizer=CHOOSE (Cost=137 Card=15603 Bytes=6818511)
   1    0   TABLE ACCESS (FULL) OF 'INCIDENT' (Cost=137 Card=15603 Bytes=6818511)
SQL> SELECT ROUND(num_rows * avg_row_len)
  2  FROM user_tables
  3  WHERE table_name = 'INCIDENT';
ROUND(NUM_ROWS*AVG_ROW_LEN)
                    6818449HTH
John