Query to find tables with excessive initial extent settings

Question

After loading a database dump we found many tables occupying large space due to large initial extents storage parameter but with very few rows and am trying to determine if it would be worth the effort to reorganize the entire schema. In other words, we are looking for a query to compare the estimated actual space that would be occupied by the table rows vs. the current size to see the space savings if we were to reorganize.
I hacked out a script to calculate the estimated size using the table stats (or 64K if estimate is lower) and compared that vs. the extents allocated to each table but this seems a rather inexact way of doing it. Is there a more accurate approach?
Doing this on Oracle database 10.2.0.4 on Windows Server 2003 SE
SELECT a.table_name,
           b.table_size_MB,
           ROUND((a.num_rows * a.avg_row_len) / (1024 * 1024),2) calc_size_MB, 
           b.table_size_MB - GREATEST(ROUND((a.num_rows * a.avg_row_len) / (1024 * 1024),2), 0.0625) savings_MB
  FROM dba_tables a,
      (SELECT segment_name, sum(bytes)/(1024*1024) table_size_MB
         FROM dba_extents
        WHERE tablespace_name like 'PMDX' and segment_type = 'TABLE'
        GROUP BY segment_name) b
WHERE a.owner = 'CAS' and a.table_name = b.segment_name
ORDER BY b.table_size_MB desc
TABLE_NAME                     TABLE_SIZE_MB CALC_SIZE_MB SAVINGS_MB
TPM06_POL_DATA_WRK_PREV                  640       493.46     146.54
TPM06_POL_DATA_WRK_CURR                  640       496.57     143.43
TPM06_POL_DATA_201006                    640        496.8      143.2
TPM06_POL_DATA_201005                    640       494.87     145.13
TPM06_POL_DATA_201004                    640       490.45     149.55
TPM07_MOV_DTLS_WRK                       256       198.66      57.34
...

Answer 1

Hi,
Didn't you check the dba_extents view with respect to the tables which you estimated.
After loading a database dump we found many tables occupying large space due to large initial extents storage parameterYou might have modified the initial extent size before to your load by pre-created tables ,which might helped out with current situation prior to this as you might be well known with your current database. Does the segement using Autoallocate or Uniform. What is the block size of DB.
- Pavan Kumar N