OLREORG (Reorganize a Database Online) › OLREORG

OLREORG

The OLREORG function of DBUTLTY combines rows in a given key range (reference group) into as few blocks as possible while reducing the effort (physical I/O) needed to retrieve the rows in native sequence, and it does this without making the data unavailable to other users. OLREORG moves rows from blocks with the fewest rows within a specified reference group (REFGROUP) to blocks with the most rows within the REFGROUP, thereby reducing the number of blocks used to contain the REFGROUP. Be aware, however, that OLREORG does not provide a one hundred percent Native Key sequence.

A reference group is a specified number of data blocks that are to be considered as a group in analyzing (reporting) and reorganizing (using OLREORG) data rows on a reference group by reference group basis. You can use statistical information on sequential data access to determine if there is a significant amount of sequential access, and of those accesses how many are to non-contiguous data blocks.

Once you have established that a given table has significant sequential access where there have been a large number of non-contiguous data block accesses, or if you know that a significant amount of sequential processing is to occur, you can execute the DBUTLTY REPORT REFGROUP option to review the current native sequence population. For information on the REFGROUP report, see REFGROUP Report.

Once your review of the current native sequence population is completed, you can decide if an online reference group reorganization should be executed to improve the native sequence population.

OLREORG runs through the Multi-User Facility so that concurrent access is available to other users of the specified table.

Note: You can interrupt or stop the execution of OLREORG without any risk to your environment by issuing a COMM REQABORT. The REQABORT is honored after each reference group is processed. In this case, no summary report is produced. The last key value processed is provided instead. This key value can be used for the FIRSTKEY= parameter if you want to start the process again by running a new DBUTLTY OLREORG.

If the OLREORG is not able to be interrupted using REQABORT, an operator cancel can be used.

For verification of the reorganization process, you can include another reference group (REFGROUP) report specification after the reference group reorganization request to see the effect of the OLREORG.