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Factors Affecting COMTI Performance.

Article ID: 196391

Article Last Modified on 2/22/2007

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SUMMARY

COM Transaction Integrator (COMTI) for Customer Information Control System (CICS) and Information Management System included with Microsoft SNA Server 4.0 provides an interface between Microsoft Transaction Server and mainframe-based applications. This article describes the major factors affecting COMTI performance. These major factors include the following:

Each of these factors is discussed in more detail below, along with specific known issues associated with each. Troubleshooting suggestions are also provided to help determine if a specific factor is causing performance problems.

MORE INFORMATION

The major factors affecting COMTI performance are discussed below.

Frequency and Type of Client Requests Made against the Microsoft Transaction Server Package

In general, the frequency of COMTI requests through SNA Server can be determined by capturing an SNA Application Advanced Program-to-Program Communications (APPC) API trace on the computer where COMTI is running. Every MC_ALLOCATE request made by COMTI is associated with a new client request against the Microsoft Transaction Server package. The frequency of MC_ALLOCATE requests within the APPC API trace file indicates the transaction load generated by COMTI. Note that the COMTI transaction load is constrained by the Microsoft Transaction Server thread pool size, described in the "Microsoft Transaction Server Thread Pool Limit of 100 for Each Package" section.



Microsoft Transaction Server Thread Pool Limit of 100 for Each Package

COMTI uses an Microsoft Transaction Server thread during the duration of an LU 6.2 conversation or transaction. Ensure that there are sufficient Microsoft Transaction Server threads to handle concurrent requests. By default, Microsoft Transaction Server 2.0 has a maximum thread pool of 100 for each package. This limits the number of concurrent COMTI requests to 100.

If you need more than 100 concurrent requests against an Microsoft Transaction Server package, you need to upgrade to Windows NT 4.0 Service Pack 4 which allows the thread pool maximum for an Microsoft Transaction Server package to be increased above 100 by setting the following registry key:

WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.
   HKEY_LOCAL_MACHINE\Software\Microsoft\Transaction Server\ 
   Package\{your package GUID}

   ThreadPoolMax: REG_DWORD: <value>
   Valid values are:  0 to 0x7FFFFFFF


SNA LU 6.2 Session and SNA Link Considerations

The following major factors affect COMTI throughput over the APPC/LU 6.2 SNA transport:

Host (VTAM, CICS/IMS) Response Time

The host response time (also referred to as the "think time") for each transaction affects the number of transactions that can be performed given the number of LU 6.2 sessions being used.

If CICS is being used, investigate the CICS region definitions for parallel session limit and contention winner limit. These values are configured in the Maximum parameter in the CICS region SESSION PROPERTIES:

SESSION PROPERTIES MAximum ==> 100, 000



The first value is the parallel session limit while the second value is the CICS contention winner limit. For COMTI use, SNA Server should be configured as the contention winner for all sessions, so the CICS contention winner limit should be 0. Also, the CICS region maximum tasks value should be sufficient to handle the concurrent client requests.

If IMS is being used, ensure that IMS has sufficient message processing regions to handle the expected load.



COMTI Security Method Being Used

The use of COMTI user or package security requires SNA Server Host Security Integration to be deployed. For best performance, the Host Account Cache service should (ideally) be running on the SNA Server computer itself, or a server on the same local network as the SNA Server computer. For more information about SNA Host Security deployment models, see the following technical white paper, co-authored by Proginet Corporation, available at the following URL:

Password Synchronization and Single Sign-On Between Multiple Platforms
http://www.microsoft.com/sna/product/progicorp.asp?A=2&B=6


If COMTI user security is used, there is validation to the Windows NT domain controller for the user domain. To support heavy stress usage from many unique Windows NT clients, consider placing a domain controller for the user's domain on the same computer or near the SNA Server computer that is supporting COMTI.

COMTI Transaction Method Being Used

If the Microsoft Transaction Server component being used with COMTI is defined to run as a transaction, then COMTI implements two-phase commit (2PC) processing when communicating to the mainframe application, under direction of the Microsoft Transaction Server Distributed Transaction Coordinator (MS DTC) process.

Transactional support involves additional communication overhead with the host application (and adds additional work for the host application), and performs slower than running in non-transactional mode.

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