Default: AMPOVR=NO
The AMPOVR constraint specifies whether CA Hyper-Buf is to override user coded AMP parameters that are supplied on the DD card. Specify AMPOVR=key to control the way that CA Hyper-Buf treats user specified AMP values.
Allowable values for key are:
AMPOVR=FORCE causes CA Hyper-Buf to always override AMP specified values. Any values specified in the AMP parameter on the associated DD card are ignored, and the OPEN proceeds with the CA Hyper-Buf calculated values for BUFNI, BUFND, and BUFFERSPACE.
AMPOVR=GREATER causes CA Hyper-Buf to override AMP specified values only if the CA Hyper-Buf calculated buffer space exceeds the AMP specified buffer space (or the buffer space calculated using the AMP values, if buffer space is not specified explicitly in the AMP parameter). If the CA Hyper-Buf buffer space is greater, OPEN continues with the CA Hyper-Buf values for BUFNI, BUFND, and BUFFERSPACE, and the AMP values are discarded. If the AMP buffer space is greater, the AMP values are used for this OPEN, and the CA Hyper-Buf values are discarded.
AMPOVR=NO (or if AMPOVR is not specified at all) causes all CA Hyper-Buf values to be discarded if any AMP values are specified on the DD card.
AMPOVR=MAX causes the OPEN intercept routine to compare the CA Hyper-Buf calculated values of BUFNI, BUFND, and BUFFERSPACE against the corresponding AMP values. In each case, the larger value is selected, and used for this OPEN. The MAXBUFSP parameter is ignored if MAX is coded for AMPOVR. The larger values of the BUFNI and BUFND parameters are used regardless of the resulting buffer space.
Note: MAX differs from the GREATER option, because the GREATER option uses either the AMP values or the CA Hyper-Buf calculated values, depending upon the comparison of the two buffer space values. This could result in a reduction of BUFNI, BUFND, or both.
For example, the user can specify BUFND=10 in the AMP parameter on the DD card of a file that is processed randomly. If the cluster is a KSDS, 4K data and 4K index, and specifies STRNO=1, the implied AMP buffer space is 45,056 (10 x 4K + 1 x 4K). The CA Hyper-Buf calculated values can be BUFND=2, BUFNI=18, BUFSP=81920.
If AMPOVR=GREATER is specified, the OPEN intercept uses the CA Hyper-Buf calculated values, since the CA Hyper-Buf buffer space is greater than the AMP buffer space. This causes a decrease in the BUFND value (from 10 to 2) and an increase in the BUFNI value (from 1 to 18) compared with the AMP specified values. The extra index and fewer data buffers is consistent with random processing, and performance should be improved, even though the data buffers are decreased.
In this same situation, AMPOVR=MAX results in BUFND=10, BUFNI=18, BUFSP=114,688. The larger values of BUFNI and BUFND are retained, and the new buffer space is calculated. The user specified MAXBUFSP is ignored in this calculation.
If AMP is not coded on a DD card, CA Hyper-Buf calculates buffers for INCLUDE mode OPENs.
ACCBIAS, a subparameter of the AMP parameter, is used to specify the type of System Managed Buffering used by a file. Because System Managed Buffering is a facility of IBM's System Managed Storage CA Hyper-Buf will not provide dynamic buffering when this parameter is specified. However, you will receive message GVB676I denoting this condition.
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