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256986 Description of the Microsoft Windows Registry
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:
- The frequency and type of client requests made against the Microsoft Transaction Server package.
- The Microsoft Transaction Server thread pool limit of 100 for each package.
- SNA LU 6.2 session and SNA link considerations.
The following major factors affect COMTI throughput over the
APPC/LU 6.2/SNA transport:- The SNA Server LU 6.2 contention winner limit.
- Preactivation of the LU 6.2 sessions.
- SNA link tuning
- Host (VTAM/FEP, CICS/IMS) response time.
- COMTI security method being used.
- COMTI transaction method being used.
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:
- The SNA Server LU 6.2 Contention Winner Limit.
COMTI only uses SNA Server LU 6.2 contention winner sessions. The number
of sessions negotiated with the host system will determine the number of
sessions available for concurrent COMTI client requests. The parallel
session limit and contention winner limit should be set to the same
value within the SNA Server APPC mode definition used by COMTI. Note
that other APPC applications may share the same Local APPC LU, Remote
APPC LU, and Mode used by COMTI. If so, sufficient sessions must be
defined to accommodate the needs of all applications. See the "Host
response time" section below for information on configuring the CICS
region parallel session limit to match the SNA Server.
Also, the Request/Response Unit (RU) size should be sufficiently
large to hold the standard message size sent between COMTI and the host
application. For example, if the host response is expected to exceed 2
KB, set the Max Send and Receive RU size to 4096 within the SNA Server
APPC mode definition. The session level pacing values will not likely
affect transaction performance because a transaction involves a single
request and single response. So, an APPC mode send and receive window of
two or more should be sufficient.
Troubleshooting Suggestions:
Capture SNA Server Data Link Control (DLC) and LU 6.2 message trace
of the connection startup and initial COMTI component use by enabling
the traces before the connection is started. Provide the traces to an
SNA Support Professional. This engineer can decode the DLC trace to
determine the parallel session limit and contention winner limits
negotiated in the Change Number of Sessions (CNOS) exchange for the
LU/LU/mode being used by COMTI. - Preactivation of the LU 6.2 Sessions.
Automatically activating LU 6.2 sessions in advance will prevent a short
delay in establishing new LU 6.2 sessions as COMTI conversation
allocation requests are made. In addition, by preactivating sessions,
SNA Server will keep these sessions active instead of deactivating those
sessions which are idle for the SESTIMEOUT period (approximately 20
seconds).
SNA Server will honor its APPC mode automatic activation limit setting
for any APPC LU/LU partnership defined within the APPC mode when the
connection is initially activated. Partnerships are defined within the
APPC-mode Partners folder.
For more information about the SNA Server SESTIMEOUT registry parameter,
see the SNA Server Reference, Chapter 8, SnaServer Service. This guide
is installed with the product and is viewable through the SNA Server
Help program option selectable from the Start menu. - SNA Link Tuning
If you are using Token Ring, Ethernet, or FDDI to communicate with your
host system, investigate DLC tuning. The following 802.2 connection
default settings should be sufficient:
- Unacknowledged Send limit defaults to 8.
- Receive Ack threshold defaults to 2.
- Maximum BTU length: 1929 for Token Ring, 1493 for Ethernet. If a 16-
Mbps Token Ring is being used, and the COMTI request or host response
will exceed this BTU length, then increase the maximum BTU length to
4105 within the SNA Server connection.
Troubleshooting Suggestions:
Capture a Microsoft Network Monitor or Sniffer(TM) trace of SNA
Server to host traffic, and provide it to an SNA Support Professional.
This engineer can use this trace to observe the Send Window and
Receive Ack threshold being used by both ends by looking at the LLC
traffic.
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:
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.