Jun 29
Question
How much space will be reclaimable in the TSM Server database if a DB reorganization is done?
 
 
Cause
After a reorganization of the TSM Server database, there was much more space reclaimed than the estimate command initial suggested.
 
 
Answer
The ESTIMATE DBREORGSTATS command only analyses the used pages. Any pages that are completely empty will not be included in the analysis. This means that heavily fragmented databases will be able to reduce their assigned capacity to much greater degree than the ESTIMATE DBREORGSTATS command suggests. From the example Q DB F=D below:
                    Available Space (MB): 115,000
                  Assigned Capacity (MB): 114,600
                  Maximum Extension (MB): 400
                  Maximum Reduction (MB): 20
                       Page Size (bytes): 4,096
                      Total Usable Pages: 29,337,600
                              Used Pages: 8,117,180
                                Pct Util: 27.7
                           Max. Pct Util: 27.7
                        Physical Volumes: 6
                       Buffer Pool Pages: 104,858
                   Total Buffer Requests: 24,711,191
                          Cache Hit Pct.: 99.11
                         Cache Wait Pct.: 0.00
                     Backup in Progress?: No
              Type of Backup In Progress:
            Incrementals Since Last Full: 0
          Changed Since Last Backup (MB): 414.17
                      Percentage Changed: 1.31
          Last Complete Backup Date/Time: 12/10/07 15:02:51
      Estimate of Recoverable Space (MB): 6,953
 Last Estimate of Recoverable Space (MB): 12/10/07 21:48:07
Currently the database can only be reduced by 20 MB, even though more space is technically free and empty. With an assigned capacity of 114,600 MB to the database, and a utilization of 27.7% we would expect that after a DB reorganization at least 82,800 MB of space would be recoverable – the amount between the actually utilized space in the database and the empty space up to the assigned capacity. However as seen the Estimate of Recoverable Space is only 6,953 MB.After the DB reorganization was completed, the assigned capacity was reduced by more than 82,800 MB.

The reason for this drastic difference, is that the estimate only covers the utilized data. Any portion of the database that is assigned, but not utilized, will not be included in the estimate. Therefore, the difference between the utilized data and the assigned capacity should be roughly included in the final estimate by the TSM Administrator when making a determination on if the reorganization is time and space effective.

written by Bosse


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