With the need to handle increasing volumes of transactions, enterprises must implement extensive and more complex system configurations that often consist of Web front-ends, WebSphere Application Servers, WebSphere MQ, WebSphere Message Broker, CICS, DB2, IMS, and other products. The tasks of systems management and workload management then become rather challenging. The CICS Transaction Server for z/OS (CICS TS) Development team recognizes this and constantly looks for ways to enhance the use and management of CICS TS.
This article discusses the numerous CICSPlex SM Workload Management (WLM) enhancements in CICS TS Version 4.2 (released June 24, 2011) that offer more control with workload istribution.
CICSPlex SM Link Neutral Dynamic Routing Algorithms
CICS TS 4.2 introduces two link neutral WLM dynamic routing algorithms:
- Link Neutral Queue Algorithm (LNQUEUE). Target regions for transactions routed through link neutral queue mode are selected based on their current task load, health state, and the existence of any active Real-Time Analysis (RTA) events and any abend compensation probabilities defined in the WLM specification (WLMSPEC) or transaction groups (TRANGRPs) associated with the workload. This is the same as the standard queue algorithm, but the link type factor isn’t calculated in the routing weight for a target region.
- Link Neutral Goal Algorithm (LNGOAL). Target regions for transactions routed through goal mode are selected based on the response time goal (either average or percentile) for the transaction being routed, as specified by the WLM component of z/OS. If a specific target can’t be identified through the goal algorithm execution, then the new LNQUEUE is applied to the remaining set of target regions. This is the same as the standard goal algorithm, but the link type factor isn’t calculated in the routing weight for a target region.
Note that if there are any transaction affinities outstanding for the transaction being routed, the affinity target region is selected regardless of the algorithm being executed.
Link neutral algorithms are beneficial for routing dynamic transactions that, for example, may require services from MVS subsystems. With the standard routing algorithms, routers focus dynamic traffic on the systems with the fastest links, which by implication probably reside in the same Logical Partition (LPAR). This could cause such subsystems to become overloaded in the local MVS image. Remote MVS images participating in the workload would be relatively underutilized. By assigning these transactions to a TRANGRP that specifies a link neutral algorithm, dynamic traffic is routed to the local and remote LPARs on a relatively even basis, spreading the load across those subsystems.
Link neutral algorithm types are intended to isolate the connection factor from the rest of the routing weight calculation. The effect is that the most remote target regions (most likely connected with the slowest telecommunications links) are equally favorable as locally connected Multi-Region Operation (MRO) regions (or even the routing region itself if it’s part of the routing target scope). Using the LNQUEUE or LNGOAL algorithm at the WLMSPEC level can affect every dynamically routed transaction. The consequence is that WLM may not necessarily choose the best target region for your dynamically routed traffic. This might hamper overall throughput.
If a link neutral algorithm is desired for a specific transaction set, an algorithm type can be specified in a WLM TRANGRP definition.
Prior to CICS TS 4.2, CICSPlex SM WLM let you specify a single dynamic routing algorithm at the WLMSPEC level (see Figure 1). This had the effect of applying the same dynamic routing algorithm to every dynamically routed transaction in the workload. Also, if the algorithm had to be changed in the same workload, all regions participating in the workload had to be simultaneously quiesced to allow the workload to be refreshed with the new algorithm specification.