How the Bitmap Resetter program works
The Bitmap Resetter program reads and analyzes the free space in each block of each data set group of an HDAM or HIDAM database. The bitmap blocks are generated and written to the VSAM entry-sequenced data set (ESDS) or OSAM data set.
To specify the criteria for determining whether a block has space, use the EXEC statement PARM operand in the JCL. You can specify one of the following values for each data set group:
- Do not reset bitmap for this data set group.
- Use the largest segment value for the data set group.
- Specify any number of bytes to use for the data set group.
For example, if a database has three data set groups, specify the following:
PARM=(HDAMDBD1,'*',,100)
This specification tells the following:
- HDAMDBD1 is the database name.
- The asterisk (*) forces the Bitmap Resetter program to make the bitmap look like IMS space management would have made it look.
- The Bitmap Resetter program does the following:
- It uses the largest segment length in data set group 1 to reset the bitmap for that data set group.
- The Bitmap Resetter program does not analyze data set group 2.
- Data set group 3 has the bitmap reflect space if the block contained a free space element of 100 bytes or more.
If you specify a value, the Bitmap Resetter program builds a bitmap indicating that there is space if the corresponding block has a free space element equal to or greater than the specified value. You can specify any value, but you should select it based on some knowledge of the segment sizes to be inserted into the database. For example, it does not make sense to specify a value of 100 if the smallest segment size is 200.
Related topic