UOW selection criteria

You can control which UOWs are selected for reorganization by using the SELECT_UOW keyword. Available values for this keyword are discussed in the following sections.

Selectively specifying UOWs for reorganization

SELECT_UOW=IOVF (the default) selects UOWs based on IOVF usage.

When this value is specified, the reorganization function will identify and reorganize only UOWs that extend into IOVF. By limiting the scope of reorganization, SELECT_UOW=IOVF significantly reduces processing I/O. In the example shown in the following figure for database dbdname, the reorganization function will consider UOWs for reorganization in area areaname only if the UOW extends into IOVF.

Sample control statements for selective UOW reorganization

SELECT_UOW=(IOVF, n1 ) selects UOWs based on a minimum specified number of IOVF control intervals (CIs) used. When this value is selected and you specify a numeric value for n1, the reorganization function will identify and reorganize only UOWs that have used at least that many IOVF CIs. This value can be used to exclude UOWs from the reorganization that have used a minimum amount of IOVF based on your assessment of CI usage. An example is shown in the following figure. For databasedbdname, the reorganization function will consider UOWs for reorganization in areaareaname only if the UOW has used at least five IOVF CIs.

SELECT_UOW=(IOVF,n1, n2) selects UOWs based on a minimum and maximum (optional) specified number of IOVF control intervals (CIs) used. When this value is selected and you specify a numeric value for n1 and n2, the reorganization function will identify and reorganize only UOWs that have used at least the minimum (n1), and no more than the maximum (n2) number of IOVF CIs. This value can be used to exclude UOWs from the reorganization that have used a minimum and maximum amount of IOVFs based on your assessment of CI usage.

Sample control statements for selective UOW reorganization based on CIs used

Either of the preceding values for the SELECT_UOW keyword can be combined with additional keywords to further limit UOW selection criteria.

The FRAGMENTATION_PERCENT keyword is used to specify the percentage of disorganization that must be detected in a UOW that extends into IOVF to qualify the UOW for reorganization.

An example of the FRAGMENTATION_PERCENT keyword is shown in following figure. For DBD dbdname, the command set reorganizes UOWs in areas areanam1 andareanam2 if the UOW extends into IOVF and the minimum user-specified percent of fragmentation, (2 percent) is detected. Reasonable fragmentation percent values range from 1 to 5 percent. Fragmentation greater than 5 percent is unlikely under ordinary circumstances.

Sample control statements for selecting fragmented UOWs

The IOVF_SAVE_THRESHOLD keyword specifies the minimum amount of IOVF that must be saved before the UOW is selected for reorganization. The amount can be specified as the number of CIs or as a percentage of the IOVF that is used by the UOW. The following figure specifies that UOWs will not be reorganized unless five or more IOVF CIs will be released.

Sample control statements for setting minimum IOVF savings by count

The following figure specifies that UOWs will not be reorganized unless 10 percent or more of IOVF control intervals that are allocated to the UOW will be released.

Sample control statements for setting minimum IOVF savings by percent

Select all UOWs for reorganization

SELECT_UOW=ALL selects all UOWs for reorganization.

This keyword and value specify that all UOWs in an area be selected for reorganization and all will be rewritten. Reorganizing all UOWs increases your reorganization execution time, but results in an area with no fragmentation.

An example for SELECT_UOW=ALL is shown in the following figure. For database dbdname, all UOWs in area areaname are reorganized.

Sample control statements for reorganizing all UOWs