Q196391: Factors Affecting COMTI Performance.
Article: Q196391
Product(s): Microsoft SNA Server
Version(s): 4.0,4.0 SP1,4.0 SP2
Operating System(s):
Keyword(s):
Last Modified: 11-JUN-2002
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The information in this article applies to:
- Microsoft SNA Server, versions 4.0, 4.0 SP1, 4.0 SP2
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IMPORTANT: This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:
Q256986 Description of the Microsoft Windows Registry
SUMMARY
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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
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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
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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
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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.
- Troubleshooting suggestions:
Capture an SNA Server DLC message trace of the throughput test and analyze the
host response time observed on the LU 6.2 sessions. The response time can be
measured for a given LU 6.2 session as follows:
SNA Server Host
----------------- ------------
Start time: FMH-5 Attach (+ data) ->
<- Data Response
End time (*): (<-) Conditional End Bracket (->)
Within an SNA Server DLC message trace, a unique LU 6.2 session is
distinguished by unique Originating Address Field (OAF), Destination Address
Field (DAF), and OAF/DAF Assignor Indicator (ODAI) values. The OAF and DAF
specified in an SNA Server session request will alternate on the host
response.
(*) NOTE: Either end may deallocate the conversation, though this is often
done by COMTI. But, it is possible for the host data response to contain the
CEB.
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.
Additional query words:
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Keywords :
Technology : kbAudDeveloper kbSNAServSearch kbSNAServ400 kbSNAServ400SP1 kbSNAServ400SP2
Version : :4.0,4.0 SP1,4.0 SP2
Issue type : kbhowto kbinfo
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