Addressing OLTP Solutions with CICS: The Transaction Server ... - Ibm

• If the client selected the system clone on the last occasion, the history_score
value is equal to the value of the configuration attribute: Same system bias.
The overall effect of the history_score value is that, after a system clone has
been used, its client has a bias toward continuing to use it. It is important to set
the Same system bias to a value greater than that specified for the Bias toward a
previously used system for a configuration. The intention is to provide a bias
toward any system used before, but particularly toward the system last used.
This will only occur if the Same system bias is greater than the Bias towards
previously used system.
Clients can remember a limited number of system clones. If a previously
unselected system is selected, the least recently used is discarded if necessary
to keep the number of known system clones to the predetermined limit. The
assumption here is that, after a time, the advantage of using a system clone that
has previously been used disappears (for example, the terminal has been
discarded, or files are no longer cached).
8.5.3.5 Projected New Load Scoring
The projected_new_load_score value is intended to represent the amount of
additional time a system would be busy if it were selected to run the current
work item. Hence it is the projected load, were this system to be selected. If the
system is selected, this amount is added to the load score and taken into
account in future decisions. However, if the system is not selected, this amount
clearly does not get added to the load score. By including this component to the
calculation, we can take into account differences between systems and select a
system that gives the fastest response time. For example, if two systems had all
other scores equal, the projected new load score would cause the selection of
the system with the greater power (that is, system speed relative to the
reference system).
Another important use of this element is specific to the ECI case, where there is
known to be a large overhead when a terminal has to be installed to run a
transaction. The load associated with an autoinstall is an attribute of the
configuration (load due to ECI autoinstall). When, in the ECI case, the workload
management algorithm can predict that an autoinstall would be needed to route
a work item to a particular system, the algorithm increments the projected new
load score by the load due to ECI autoinstall. This heavily biases against
systems where a terminal installation would be needed to run the transaction.
8.5.3.6 Score limiting
System clones with a total_score greater than the maximum score permitted are
rejected as unsuitable. The default settings ensure that all system clones with a
health of 5 will be rejected. The limiting is important only if all potential system
clones are in this state. In this case, an alternative partition or the CICS default
system is used.
Chapter 8. Using CICS System Manager for AIX 127