Tuning the recovery process (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. The optimized number of I/O buffers are used for writing database records from input image copy data set.

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 expression:

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 an 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

To change the value in the I/O buffer for a database data set, specify BUFND or BUFNO by using the JCL DD card of the database data set.

Buffer tuning for input data sets

The default value of the I/O buffer of the image copy data set, the log data set, or the change accumulation 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 performance by increasing the buffer numbers.

The buffer number can be changed by specifying the value for BUFNO by using the JCL DD card of the image copy database data set, the log data set, or the change accumulation data set.