Eliminating and reducing searches for unavailable resources

When a resource is unreachable in a network, futile attempts to reach it can still occur. Excessive searching for unreachable resources can adversely affect network performance. Therefore, VTAM® provides search reduction support, which limits requests for resources that have been found to be unreachable.

Search reduction is turned on in VTAM by using the VTAM start option SRCHRED=ON (the default value is OFF). See IBM-supplied default start option list for more information about the SRCHRED start option. If search reduction has been turned on, the SRTIMER and SRCOUNT operands can be specified on the CDRSC definition statement or on the GROUP definition statement in a CDRSC major node.

The SRTIMER operand specifies for the resource the time period (in seconds) during which requests for the resource will be limited. This time period begins when it is determined that the resource is unreachable. Once the time period expires, the next request for the resource causes VTAM to issue another search for it. This operand overrides the value of the SRTIMER start option for this CDRSC. In the CDRSC major node that follows, all the cross-domain resources except R50A721 default to an SRTIMER value of 600 seconds, as a result of the SRTIMER specification on the GROUP definition statement.

The SRCOUNT operand specifies for the resource the number of subsequent search requests to be limited after it is determined that the resource is unreachable. Once this limit is reached, the next request for the resource causes VTAM to issue another search for it. This operand overrides the value of the SRCOUNT start option for this CDRSC. See IBM-supplied default start option list for more information about the SRCOUNT start option. In the CDRSC major node that follows, all the cross-domain resources except ECHO50A have a default SRCOUNT value of 15 as a result of the SRCOUNT value specified on the GROUP definition statement.

Search reduction for a resource is stopped when either of these two thresholds is reached. For more information about specifying search reduction values, see the z/OS Communications Server: SNA Resource Definition Reference.

*  =====&gt; BEGINNING OF DATA SET A02CDRSC
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*                                                                     *
*   A02CDRSC - VTAM CROSS-DOMAIN RESOURCE MAJOR NODE - SUBAREA A02    *
*                                                                     *
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          VBUILD TYPE=CDRSC,CONFGDS=CDRSCKPT
 NETA     NETWORK NETID=NETA
 CDRGRP1  GROUP CDRM=A500N,SRTIMER=600,SRCOUNT=15
 NEGAP50  CDRSC
 ECHO50A  CDRSC SRCOUNT=1500  * Override default
 A50A721  CDRSC SRTIMER=0     * Override default
 W3324802 CDRSC
*  =====&gt; END OF DATA SET A02CDRSC