When viewing the virtual byte size of any SNA Server service or Win32
application which uses the SNA Server API's, Windows NT Performance Monitor
shows the Win32 process' virtual byte size to be larger than 154MB.
SNA Server reserves a 154MB contiguous region in the process' virtual
address space, though only 64KB of physical memory is initially allocated
or committed. Additional physical memory is allocated only when needed.
Also, this memory is shared between all SNA Server processes running on the
computer, and only one copy is allocated even if there are several SNA
Since this large virtual memory area is not actually allocated out of
available physical memory, other processes running on the computer are not
be affected, nor does it affect the Windows NT page file. The committed
memory can be found by viewing the "working set" size of each process.
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
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:
A buffer pool audit has been triggered by a pool extension.
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
Comname Pid Trusted Hdrs Elts
None, unless there is some other problem. In that case, report
this log along with any others.
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
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.
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.