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Calculating Oracle average row length

Oracle Tips by Burleson Consulting

Calculating the average row length for rows in a table is done when you analyze the table (using dbms_stats, or automatically in Oracle 10g), but there are times when you need an ad-hoc way to calculate the average row length within an Oracle table, especially when doing capacity planning.

Robert James Hanrahan has contributed a fascinating way to calculate the real average row length for an Oracle table.


Here is a sophisticated PL/SQL procedure to calculate average row lengthIt works, but it has an issue because you cannot use VSIZE on BLOB data columns, and it could be re-done using dbms_lob.getlength(BLOB_COLUMN) to get an accurate average_row_length for rows with a BLOB column..

To find the actual size of a row I did this:

/* TABLE */

select
3 + avg(nvl(dbms_lob.getlength(CASE_DATA),0)+1 +
               nvl(vsize(CASE_NUMBER   ),0)+1 +
               nvl(vsize(CASE_DATA_NAME),0)+1 +
               nvl(vsize(LASTMOD_TIME_T),0)+1
              ) "Total bytes per row"
from
   arch_case_data
where
   case_number = 301;

Total bytes per row
--------------------
                3424

/* INDEX */

 select sum(COLUMN_LENGTH)
   from dba_ind_columns
  where  TABLE_NAME = 'ARCH_CASE_DATA';

SUM(COLUMN_LENGTH)
------------------------
                      22

So, the total bytes used is 3424+22.
 


 

 

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