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

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126 CICS for AIX as the Transaction Server 8.5.3.1 Load Scoring The load_score value is a measure of the outstanding level of work that remains to be completed by a system clone. When a system clone is selected, its load is increased to reflect that an additional piece of work has been routed to it. The size of the load that is added is equal to the program or transaction “Execution time on a reference system” divided by the number of application servers in the clone to which it has been routed. When the work item is complete, the response is detected by the workload management client, and the system clone′s load is decreased by the amount that was added when the system was selected. The workload management client code runs a simulation to predict how busy its candidate systems are. This simulation is preferred to an actual measurement of how busy they are; as with the time delays involved, such a system would not form a stable servo loop. The overall effect of the simulation is to discourage the selection of systems that have large numbers of sessions or recently have been given large amounts of work. The workload management algorithm acts on static data provided by CICS SM together with dynamic information it has obtained by remembering the routing decisions it has made and observing the responses. Note that the dynamic information is obtained from all of the processes that use one workload management cache manager and therefore run on the same node as the workload management cache manager. There is no sharing of dynamic information between workload management cache managers: each cache provides information that its clients use to make decisions independent of clients on another node. As a consequence, nodes running multiple workload management client processes have a larger pool of dynamic information on which to balance the workload than nodes running one or very few workload management client processes. 8.5.3.2 Health Scoring The health_score value is determined by taking the health of a system clone (as supplied by the health monitor) and applying an adjustment value corresponding to the health of the region. Health values range from 1 (excellent) to 5 (very poor). The use of these health values discourages the selection of system clones that the health monitor reports as inferior. 8.5.3.3 Connection Scoring The connection_score value is typically constant for a given system. It is determined by multiplying the reference time for a round trip on the connection by the connection delay weighting. The value can change only when a new configuration is activated. 8.5.3.4 History Scoring The history_score value is calculated according to which of these three different situations applies: • If the client has not selected the system clone before, the history_score value is zero. • If the client has selected the system clone before, but not on the last occasion, the history_score value is equal to the value of the configuration attribute: Bias towards previously used system.
• 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
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Addressing OLTP Solutions with CICS
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Take Note! Before using this inform
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iv CICS for AIX as the Transaction
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9.4 Security Issues on the Internet
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viii CICS for AIX as the Transactio
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x CICS for AIX as the Transaction S
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xii CICS for AIX as the Transaction
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The Team That Wrote This Redbook xi
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xvi CICS for AIX as the Transaction
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2 CICS for AIX as the Transaction S
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1.2 Complex OLTP Business Environme
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Figure 2. OLTP Complex for XYZ Insu
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By using common application program
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1.5 OLTP Market 10 CICS for AIX as
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Figure 5. OLTP Market Segmentation
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14 CICS for AIX as the Transaction
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2.1 IBM Software Servers 2.1.1 Lotu
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2.2.1 CICS Clients V1.1.0 A Transac
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2.2.4 CICS Internet Gateway for AIX
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3.1 Services CICS for AIX is a very
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3.1.2 CICS API 24 CICS for AIX as t
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3.1.3.1 Terminal Users and CICS Reg
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3.2 Implementation 3.2.1 Components
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3.2.2 Processes 3.2.1.3 Application
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3.3.1 DCE RPC 3.3.2 TCP/IP 32 CICS
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Figure 9. Interconnection Using Enc
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connect to a PPC Gateway server mac
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Figure 12. Interconnection Using TC
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3.4.3 Configuration 3.4.4 Managing
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3.4.6 Intersystem Communication CIC
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3.4.8 Data Location 44 CICS for AIX
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3.4.11 Operations plan to cope with
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3.5 Summary 48 CICS for AIX as the
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Figure 13. Application Server Model
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4.2.1 CICS External Call Interface
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By means of mapping files, you can
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4.3 Versions 56 CICS for AIX as the
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4.4 Sample Network Configurations 4
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4.5.1 CICS Client for OS/2 60 CICS
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4.5.2 CICS Client for DOS 62 CICS f
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4.5.5 CICS Client for AIX CICS Clie
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4.6 Summary 68 CICS for AIX as the
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5.1.1 DCE Threads 5.1.2 Remote Proc
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The GDS is based on the CCITT X.500
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egion or server it is looking for.
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How Customers Can Get ITSO Redbooks
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design. The process of composing a
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A year later ISC gave SQL formal in
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designing efficient applications 15
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