Using the VSAM-Buffer-Pool report

The primary usefulness of the VSAM-Buffer-Pool report is to calculate how many I/O operations were required to read to or write from the subpool.

You might want to increase buffer pool size to see if you can decrease the number of I/O operations. You might also want to turn on background write. Or, if the number of I/O operations is increasing over time, you might need to reorganize your database.

To calculate the number of I/O operations required to read to or write from the buffer pool, use the following formula:

Total I/O equals the sum of:

1. The number of times a CI had to be read into the buffer from the database (NUMBER of CONTR INT READ FROM EXTERNAL STORAGE field in the report).
2. The number of times a buffer had to be written to the database (NUMBER OF VSAM WRITES INITIATED BY IMS field in the report).
3. The number of times a buffer had to be written to the database so a new CI could be read into the buffer (NUMBER OF VSAM WRITES TO MAKE SPACE IN THE POOL field in the report).