Example of specifying buffers

Review this example of specifying buffers to see how the Buffer Size Specification facility (DSPBUFFS) overrides the number of buffers to expand the total amount of buffer storage used.

Company XYZ shares RECON data sets between two processors. Processor A is an ESA machine, processor B is not— a coexistence environment involving an earlier release of IMS is on processor B. In this case, each IMS system uses a separate copy of the following example.

XYZ frequently runs batch jobs using DBRC under TSO. However, tight region restrictions exist for jobs run under TSO, so they must limit the amount of storage used by DBRC in these circumstances. However, DBRC storage is not limited when executing as a control region task, so they have replaced DSPBUFFS with the following values:

DSPBUFFS example

DSPBUFFS CSECT ,                   DECLARE NBR OF INDEX & DATA BUFFER
         DC    CL8'DSPBUFFS'       REQUIRED EYECATCHER FOR DUMPS
*
*                                  processor A (LSR) SETUP
LSRONLIN DC    AL2(10,26)          ESA ENVIRON - IMS ONLINE DBRC
LSRCICS  DC    AL2(6,12)           ESA ENVIRON - CICS USE OF DBRC
LSRBATCH DC    AL2(6,14)           ESA ENVIRON - OFFLINE/BATCH DBRC
*
*                                  processor B (NSR) SETUP
NSRONLIN DC    AL2(4,9)            NONESA ENVIRON - IMS ONLINE DBRC
NSRCICS  DC    AL2(2,2)            NONESA ENVIRON - CICS USE OF DBRC
NSRBATCH DC    AL2(3,5)            NONESA ENVIRON - OFFLINE/BATCH DBRC
         END

When run as an IMS online region, DBRC in processor A (LSR) creates 10 index buffers and 26 data buffers to be shared between the 2 active RECON data sets. In processor B (NSR), DBRC assigns 4 index buffers and 9 data buffers to each RECON data set. When both active RECON data sets are opened for NSR, a total of 8 index and 18 data buffers are implied. Remember that under NSR, when the spare RECON data set is opened, it too will be assigned 4 index and 9 data buffers. For brief periods of time in processor B, the total number of index and data buffers used are 12 and 27, respectively.

Under LSR, when the spare RECON data set is opened (initially in NSR mode, a VSAM requirement), it is assigned 2 index and 2 data buffers. These values cannot be overridden. For brief periods of time in processor A, the total number of index and data buffers used are 12 and 28, respectively. Thus the total amount of storage that is used for RECON buffers is approximately the same in both processors.

When running batch jobs, DBRC in processor A creates 6 index buffers and 14 data buffers to be shared between the 2 active RECON data sets. In processor B, DBRC assigns 3 index buffers and 5 data buffers to each RECON data set opened with NSR buffering. Again, during those periods of time that all 3 RECON data sets are open, the total amount of buffer storage used is approximately the same in both processors (8 index and 16 data buffers in processor A, 9 index and 15 data buffers in processor B).