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

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3.4.6 Intersystem Communication CICS provides good intercommunication facilities. However, you should consider whether CICS systems really do need to be interconnected. There may in practice be no real decision to be made because the issue is forced in some way—for example, data on a remote system has to be accessed by user transactions, and it is infeasible to replicate the data. If intersystem communication is used, it is sensible to optimize its use from several viewpoints: • Performance The fewer calls to remote systems, the less processing work to be done. Each time there is communication over a network component, there is an inherent delay no matter what the speed of the actual link. • Complexity of the configuration With an increased amount of intercommunication, the overall CICS environment becomes more complex, and determining whether all of the links are working becomes less straightforward. • Ease of problem determination In a highly interconnected environment, it can become difficult to trace a problem as there are many components interacting. Problems of poor performance become more difficult to track down. It becomes difficult to capture all activity related to one system when that system may be connected to three or four others. Users will report a problem, but they will have no idea where in the complex the problem actually is. 3.4.6.1 Selecting a Protocol When selecting a protocol for the implementation of intersystem communication, ensure that it enables you to connect the required systems and provides the required level of synchronization. For example, CICS over TCP/IP is easy to set up and has advantages in that the session it creates remains established while both systems remain active. It does not provide synchronization level 2 support though. If your application actually requires synchronization level 2, you must use Encina PPC TCP/IP or Encina PPC Gateway. In the case where a CICS for AIX region is running multiple applications, it may be necessary to have several communication protocols in use between the local region and other CICS regions. This situation is to be avoided where possible, however, to keep the configuration as simple as possible. Table 3 summarizes the protocols supported in CICS for AIX. Table 3 (Page 1 of 2). Communication Methods Used by CICS across TCP/IP and SNA CICS family TCP/IP 42 CICS for AIX as the Transaction Server Best for Restrictions Communication at synchronization level 0 or 1 with CICS on Open Systems, CICS on Windows NT, CICS for OS/2, and IBM CICS Clients across TCP/IP DTP is not supported. CICS user security must be configured with care over these connections as it is not possible to reliably authenticate (identify) the remote system.
Table 3 (Page 2 of 2). Communication Methods Used by CICS across TCP/IP and SNA Encina PPC TCP/IP Local SNA Encina PPC Gateway Best for Restrictions Communication at synchronization levels 0, 1, or 2 with other CICS on Open Systems regions or Encina PPC applications Fastest synchronization level 0 or 1 communication with remote LU 6.2 (APPC) systems. These connections can be used to connect to any CICS product. Synchronization levels 0, 1, and 2 communication with remote LU 6.2 (APPC) systems. These connections can be used to connect to any CICS product. If your region is using DCE CDS as a name service, the remote region or application must be in the same DCE cell as the local region. A supported SNA product must be installed on the same machine as the CICS region. When using AIX SNA, Encina PPC Gateway must be installed on a machine along with a supported SNA product. If your region is using DCE CDS as a name service, both the PPC Gateway and your local region must be in the same DCE cell. Understand how intersystem sessions are created. The methods vary with the protocol. In an environment where there are frequent requests between the two systems, this session setup and shutdown activity can represent an unnecessary overhead, which could be avoided through the selection of an appropriate protocol. For example, with CICS family TCP/IP, a session is created between the two systems and stays active for as long as the two systems remain active. Encina PPC TCP/IP, however, creates a session solely for the duration of the request. 3.4.7 Choosing an Intercommunication Facility CICS provides a number of different intercommunication facilities that complement each other. One facility will usually be more suitable and efficient for a given application than another. Below we consider the attributes of each facility and describe when it may be best used. 3.4.7.1 Function Shipping Function shipping provides an easy means of accessing remote data resources, such as files or temporary storage queues. Each request is sent separately to the remote system, however. So, depending on the amount of data to be accessed, it may be more efficient to use a DPL or a DTP request. Consider the case where a record is updated on a remote system. There will be one round trip to the remote system to get the record, a second to rewrite, followed by a third at syncpoint time, a total of three round trips to the remote system. A DPL program could have completed the request in a single trip by being called so that it performed synchronization processing prior to its return. The DPL case does require programming effort to implement it and there are recovery considerations to take into account, such as, What if the DPL program committed its update and there is a failure on the local system? So the choices Chapter 3. CICS for AIX 43
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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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7.2.2 Single-Phase and Two-Phase co
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Figure 28. Switching Access among D
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Figure 30. CICS Access to Remote DB
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emote DRDA database. Information ab
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As the COMMAREA has an allowable ma
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7.5 Summary 108 CICS for AIX as the
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8.2 Workload Management 112 CICS fo
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8.4.2 System Management Application
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Figure 36. The CICS SM GUI 8.4.6 Di
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Figure 37. CICS SM Component Distri
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Figure 38. Combining Resources 122
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8.5.2 The Reference System 124 CICS
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8.6 Planning Considerations for CIC
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9.1 Some Terminology 9.2 Services 1
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Figure 41. CICS Internet Gateway fo
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9.3.3 Data Integrity The Web was or
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9.3.5 High Availability The drawbac
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or employee records, eavesdropping
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• Type, size, and quantity of rec
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10.3.3 Writing ECI and EPI Applicat
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10.8 Summary 154 CICS for AIX as th
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11.1 The Big Picture 158 CICS for A
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11.2 User Access 160 CICS for AIX a
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Figure 44. Access to Various DB2 Da
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takes place over TCP/IP or SNA comm
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provide greater protection in the u
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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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