Microsoft KB Archive/246590

= COMTI Cannot Use All Available LU6.2 Sessions =

Article ID: 246590

Article Last Modified on 10/21/2005

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APPLIES TO


 * Microsoft SNA Server 4.0
 * Microsoft SNA Server 4.0 Service Pack 1
 * Microsoft SNA Server 4.0 Service Pack 2
 * Microsoft COM Transaction Integrator for CICS and IMS 1.0 SP1
 * Microsoft COM Transaction Integrator for CICS and IMS 4.0 SP2

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This article was previously published under Q246590



SYMPTOMS
When a COM Transaction Integrator for CICS and IMS (COMTI) component attempts to establish multiple APPC conversations to a host transaction program (TP) over a given APPC triplet (Local LU, Remote LU, and Mode), COMTI may be unable to use all of the available sessions that were negotiated during the Change Number of Sessions (CNOS) exchange. For example, if a maximum parallel session limit of 6 is negotiated for a particular LU triplet, COMTI may only see 3 of the sessions. It will never attempt to use the remaining available sessions, regardless of the load or volume of data that may be arriving from upper-layer applications.



CAUSE
By design, COMTI APPC conversations can only be established over LU6.2 contention winner (conwinner) sessions. In many cases, the conwinner-session limit negotiated during the CNOS exchange is less than the total parallel sessions supported for the mode. Only conwinner sessions are visible to COMTI.



RESOLUTION
A supported feature that modifies the product's default behavior is now available from Microsoft, but it is only intended to modify the behavior that this article describes. Apply it only to systems that specifically require it. This feature may receive additional testing. Therefore, if the system is not severely affected by the lack of this feature, we recommend that you wait for the next Microsoft SNA Server version 4.0 service pack 3 that contains this feature.

To obtain this feature immediately, contact Microsoft Product Support Services. For a complete list of Microsoft Product Support Services telephone numbers and information about support costs, visit the following Microsoft Web site:

http://support.microsoft.com/contactus/?ws=support

The English version of this feature should have the following file attributes or later:

NOTE: Date and time information will be provided as soon as it becomes available.

NOTE: Because of file dependencies, the most recent fix that contains the preceding files may also contain additional files.



STATUS
Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article.



MORE INFORMATION
When COMTI formulates an MC_ALLOCATE request to initiate a conversation to the remote TP, it sets the return control (rtn_ctl) attribute to AP_WHEN_CONWINNER_ALLOC to specifically ask for a conwinner session. Considering that COMTI is the initiator of all transactions, making use of conwinner sessions is the most optimal choice when performance is a concern. There is no bidding overhead incurred for conversation startup. When all conwinner sessions are in use, available contention loser (conloser) sessions will not be useable by COMTI. Contention loser sessions are also known as partner contention winner sessions.

The feature update mentioned in this article simply allows COMTI to make use of all available sessions regardless of whether they are conwinners or conlosers. This has been achieved by setting the MC_ALLOCATE rtn_ctl attribute to AP_WHEN_SESSION_ALLOCATED. By default, SNA Server exhausts all cowinner sessions first before resorting to the contention losers.

For additional information, click the article number below to view the article in the Microsoft Knowledge Base:

196391 Factors Affecting COMTI Performance

Keywords: KB246590

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