SNA Server Windows Client Memory Tuning

• Microsoft SNA Server for Windows NT, versions 2.0, 2.1, 2.11, 2.11 SP1, and 3.0

SUMMARY

The following tuning suggestions can reduce conventional memory usage on Windows 3.x and Windows for Workgroups 3.x clients running the SNA Server Windows 3.x client software. If the machine is running low on available conventional memory (memory between zero and one megabyte), you may see the following problems, no matter how much RAM you have installed:

• One of the following error message appears:

        Out of Memory
  

        SNA Server Error 546: Cannot establish connection with SNA Server
  

        NAP not started
  

• The SNA Server Windows client icon (WNAP.EXE) does not maintain its sponsor connection
• A 5250 emulator displays the following APPC error:

        Primary return code = F011        (AP_UNEXPECTED_DOS_ERROR)
        Secondary return code = 00000008  (out of memory)
  
  

• Applications the do not properly handle low memory situations cause general protection (GP) faults or stop responding (hang).

MORE INFORMATION

Windows client memory tuning suggestions:

SNA Server Windows Client Memory Allocation

By default, WNAP reserves enough internal buffers to handle connections through several servers. If you only connect through one or two SNA Servers, you can add the following entry to the [wnap] section of WIN.INI:

   maxpipes=6

Stop and restart WNAP so this change can take effect.

Disabling Network DDE on Windows for Workgroups Version 3.11 Machines

A significant amount of conventional memory can be gained by disabling Network DDE, if it is not being used. To do this, run the Windows for Workgroups 3.11 Control Panel, choose Network, choose Startup, and clear the Network DDE check box. Quit and restart Windows for Workgroups so this change can take effect.

You can make more conventional memory available by removing any unnecessary drivers or terminate-and-stay-resident (TSR) programs from the configuration, and maximizing the use of available upper memory block (UMB) areas if MS-DOS 5.0 or later is being used.

Identify Low Memory Situations

You can use the Heap Walker utility (HEAPWALK.EXE), included with the Windows 3.1 SDK, to help identify low conventional memory situation in Windows:

• Select the Sort/Address option to view memory allocation from low to high memory addresses. Conventional memory addresses start with 000xxxxx while virtual addresses start with 80xxxxxx.
• All segments which appear as Fixed memory (where the FLG field is set to F) cannot be moved or discarded by Windows. Low conventional memory problems occur when excessive Fixed memory regions occupy conventional memory space, and very few free conventional memory areas are available, even though the may be large amounts of virtual memory available.
• You can save Heap Walker information to a file called HWG0x.TXT (where x increments from 0 - 9) by choosing Save from the file menu.