Tuning the image copy process (IMS compatible JCL)
You can tune the image copy process that is called from IMS compatible JCL.
I/O buffer tuning for database data sets
IMS HP Image Copy optimizes the number of I/O buffers and uses the optimized number of I/O buffers for a database data set. This is effective for the standard I/O process.
- The database data set is the primary index data set of HIDAM, HISAM, or SHISAM, or a secondary index.
- The database is HDAM, HIDAM, HALDB, or DEDB and the high performance I/O (HPIO) interface is disabled.
The optimized number of I/O buffers is as follows:
- VSAM data sets
- IMS HP Image Copy sets optimized number of buffers in
BUFND of VSAM. The optimized BUFND is calculated by the following expressions:
Database CI size Optimized number of BUFND Less than 2 K Number of CIs in 1 CA x 1/2 Equal or greater than 2 K Number of CIs in 1 CA x 1/4 - OSAM data sets
- IMS HP Image Copy sets optimized number of buffers in
BUFNO of OSAM. The optimized BUFNO depends on the size of the OSAM block.
Database block size Optimized number of BUFNO size < 6144 (2 K x 3) 30 6145 =< size =< 8192 (2 K x 4) 24 8193 =< size =< 10240 (2 K x 5) 20 10241 =< size =< 12288 (2 K x 6) 17 12289 =< size =< 14336 (2 K x 7) 15 14337 =< size =< 16384 (2 K x 8) 13 16385 =< size =< 18432 (2 K x 9) 12 18433 =< size =< 20480 (2 K x 10) 11 20481 =< size =< 22528 (2 K x 11) 10 22529 =< size =< 24576 (2 K x 12) 09 24577 =< size =< 28672 (2 K x 14) 08 28673 =< size 07
If you need to change the optimized number, specify BUFND or BUFNO using the JCL DD card of the database data set.
If you use the High Performance I/O (HPIO) process, the buffer number of the database access is automatically determined by HPIO. In this case, you cannot change the number by using IMS HP Image Copy JCL.
Buffer tuning for image copy data sets
The default value of the I/O buffer of the image copy data set is BUFNO=50.
The buffer numbers depend on what tape unit is being used. If the image copy data set resides on a DASD, you can improve the performance by increasing the buffer numbers.
To change the value of the I/O buffer of the image copy data set, specify BUFND or BUFNO using the JCL DD card of the image copy database data set.
IDRC-enabled tape devices
When you use a tape for output image copy data set on an IDRC-enabled device, use the FABJCMP2 compression routine. FABJCMP2 compresses the FSE portion of the database record in the image copy data set. The FSE compression in FABJCMP2 is done by the program of IMS HP Image Copy before the data is written to tape, then, in the device, IDRC compresses the data through the hardware process. As a result, the output data volume is decreased by the FSE compression and elapsed time is decreased.
Other compression routines are ignored when used with IDRC, and image copy data set is not compressed by IMS HP Image Copy.