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Q239861: SNA Server Host Print Service Supports 1,024 3270 Print Sessions

Article: Q239861
Product(s): Microsoft SNA Server
Version(s): WINDOWS:3.0,3.0 SP1,3.0 SP2,3.0 SP3,3.0 SP4,4.0,4.0 SP1,4.0 SP2
Operating System(s): 
Keyword(s): kbsna300sp1 kbsna300sp2 kbsna300sp3 kbsna300sp4 sna4 kbsna400sp1 kbsna400sp2
Last Modified: 11-JUN-2002

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The information in this article applies to:

- Microsoft SNA Server, versions 3.0, 3.0 SP1, 3.0 SP2, 3.0 SP3, 3.0 SP4, 4.0, 4.0 SP1, 4.0 SP2, 4.0 SP3 
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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
=======

The host print service (Snaprint.exe) included with SNA Server supports a
maximum of 1,024 3270 print sessions. 3270 print sessions are limited to 1,024
because of the threading model used by the Snaprint service. The Snaprint
service can create a maximum of 32 threads to service the 3270 print sessions.
Each thread can support up to 32 sessions. Thirty-two threads supporting a
maximum of 32 sessions each yields 1,024 sessions.

Each of the first 32 3270 print sessions will cause the Snaprint service to
create a new thread. Therefore, if the Snaprint service is configured with 32
3270 print sessions, each print session will be assigned to its own thread.

Additional 3270 print sessions are assigned to the existing threads in a
round-robin order to ensure that the sessions are balanced among the 32
threads.

For additional information about the latest service pack for SNA Server 4.0,
click the article number below to view the article in the Microsoft Knowledge
Base:

  Q215838 How to Obtain the Latest SNA Server Version 4.0 Service Pack

MORE INFORMATION
================

The limit of 1,024 3270 print sessions is also a practical limit based on
performance testing. The following are the recommended number of print sessions
per host print service:

- Maximum simultaneously active GDI printer sessions: 240
- Recommended maximum simultaneously active non-GDI printer sessions: 500

Please refer to the Microsoft SNA Print Service White Paper
(http://www.microsoft.com/sna/library/snaprint2.exe) for complete details on the
performance test results.

The Snaprint service has been modified to support more than 1,024 3270 print
sessions for those customers who require more 3270 print sessions for host print
service.

CAUTION: The use of more than 1,024 print sessions should only be considered in
environments where printing throughput is light. Use the Microsoft SNA Print
Service White Paper (http://www.microsoft.com/sna/library/snaprint2.exe) as a
guideline when determining if the print requirements are light. The use of more
than 1,024 print sessions may result in unacceptable printing performance. Other
unpredictable results may also occur with high volume printing due to the
resources (for example, GDI, memory, CPU) required for heavy printing loads.

After you apply the updated print server binaries, the following registry entries
need to be added to allow more than 1,024 3270 print sessions.

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.

1. Start Registry Editor (Regedt32.exe).

2. Locate the following key in the registry:

  
  HKEY_LOCAL__MACHINE\System\CurrentControlSet\Services\SnaPrint\Parameters

3. On the Edit menu, click Add Value, and then add the following registry
  value:

  Value Name: Max3270Sessions
  Data Type: REG_DWORD
  Value: <Number of 3270 Print sessions>

  Note: The range for this parameter is 1 through 4096.

4. On the Edit menu, click Add Value, and then add the following registry
  value:

  Value Name: OpenClose
  Data Type: REG_SZ
  Value: Yes

  This parameter can have any value. It is enabled as long as the entry exists.
  A value of Yes is shown for simplicity.

5. Quit Registry Editor.

Each thread created by the Snaprint service for 3270 print sessions still
supports a maximum of 32 sessions. However, the Snaprint service can now create
more than 32 threads. The maximum number of threads that can be used for 3270
printing is obtained by dividing the Max3270Sessions registry setting by 32
(rounding up if necessary), because each thread can support up to 32 sessions.
As was the case before this change was made, the Snaprint service does not
assign a second session to any thread unless it has started the maximum number
of threads and assigned one session to each of these.

If Max3270Sessions is set to 3000, the print service will create 94 threads
(3000/32 = 93.75). If there are 94 print sessions, each of the 94 threads will
have 1 session assigned to it. The 95th session will be assigned to the first
thread created, giving that thread 2 sessions.

Using the maximum numbers of sessions, which is now 4096, the Snaprint service
now supports a maximum of 128 threads for 3270 print sessions.

Note: Setting Max3270Sessions unnecessarily high will result in unnecessarily
high thread and memory usage.

The OpenClose registry setting specifies that the Snaprint service opens a
printer at the beginning of a print job and closes the printer at the end of the
print job. By default, the Snaprint service opens all defined printers at print
service startup. Using this option (especially in conjunction with a large
number of print sessions) prevents the number of open printer handles from being
unnecessarily high.

If the OpenClose option is set then the Monitor Job (for example Request Definite
Response) option cannot be used on the 3270 printer sessions. If the Monitor
Job/Request Definite Response option is specified on any session, it is
ignored.

If these registry entries are not set, the Snaprint service will continue to
support a maximum of 1,024 3270 print sessions, as it did prior to applying
these updates.



Additional query words:

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Keywords          : kbsna300sp1 kbsna300sp2 kbsna300sp3 kbsna300sp4 sna4 kbsna400sp1 kbsna400sp2 
Technology        : kbAudDeveloper kbSNAServSearch kbSNAServ300 kbSNAServ400 kbSNAServ300SP3 kbSNAServ300SP1 kbSNAServ400SP1 kbSNAServ400SP2 kbSNAServ400SP3 kbSNAServ300SP2 kbSNAServ300SP4
Version           : WINDOWS:3.0,3.0 SP1,3.0 SP2,3.0 SP3,3.0 SP4,4.0,4.0 SP1,4.0 SP2
Issue type        : kbinfo

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