SNA Server Processes Show Huge Virtual Byte Size in PerfMon

MORE INFORMATION

SNA Server processes running locally on a Windows NT computer communicate with each other using a shared memory region. Each SNA Server process (that is, SnaBase, SNA Server, link services, and applications which use the SNA API's) communicate with other SNA Server processes on the computer by writing to buffers in this memory region which is then available for other SNA Server processes to access.

When SnaBase is started, it reserves this shared memory region as a Windows NT virtual memory mapped file. The size of this file is determined by the size of all possible SNA Server internal communication buffers which can potentially be allocated (on SNA Server 2.11, this is 154,300,416 bytes). However, out of this large potential size, the initial allocation size is less than 64KB (16KB for process headers, 32KB for elements and 8KB for headers).

SNA Server logs event 684 and 685 to indicate changes in the buffer pool memory allocation. Event 684 is logged when over half of the maximum number of buffer pools has been allocated. Event 685 is logged if Windows NT has returned an error to our VirtualAlloc call, or if the maximum number of buffer pool extensions have been allocated. Full internal tracing on the component logging these events indicates the cause of the 685 error. The text for these events are included below:

   Event 684
   A buffer pool audit has been triggered by a pool extension.

   EXPLANATION

   This audit contains information about the size of the buffer pool,
   how many headers and elements each process is using, etc.

                   Pool      Free     Alloced      Max

   Trusted Hdrs
   Trusted Elts
   Non-Trusted Hdrs
   Non-Trusted Elts

   Comname    Pid    Trusted   Hdrs   Elts

   SnaBase
   SnaServr
   SnaDlc1
   ...


   ACTION

   None, unless there is some other problem. In that case, report
   this log along with any others.



   Event 685

   An attempt was made to extend a buffer pool, but the related pool
   had reached its maximum size. The affected component is terminating,
   and an audit of the buffer pools just before termination is attached

   EXPLANATION
   This error is almost always due to either an SNA component (including
   possibly an emulator) losing buffers or a slow emulator (or RUI
   application) using a session without pacing.

   ACTION
   Contact your support personnel.

   Excessive logging of this event may indicate that an SNA Server process
   running on the machine is not releasing buffers properly, which could
   indicate a potential memory leak.