Pathway/XM System Management Manual

Overview of Configuring and Managing Pathway/XM
Compaq NonStop™ Pathway/XM System Management Manual—426761-001
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How Pathway/XM Balances the Transaction
Workload
Pathsend requesters are either user-written or provided as part of Compaq or third-party
products. For example, workstation clients that use Compaq NonStop™ Remote Server
Call/MP (RSC/MP) communicate with Pathway servers indirectly by means of Pathsend
requesters created by RSC on behalf of the clients.
Although LINKMON processes are visible in the Pathway/XM environment, they are
not configured or managed by PXMCFG or PXMCOM. However, you can obtain status
information about LINKMON processes through PXMCOM.
How Pathway/XM Balances the Transaction
Workload
You define the system resources (Expand nodes and processors) to be used for load
balancing by means of logical nodes in your Pathway/XM configuration. A logical node
specifies available system and processor resources to be used for requesters or servers.
You define one or more logical nodes for client resources and one or more logical nodes
for server resources. One process broker (PB) process, running as a process pair, is
provided for each logical node in the Pathway/XM environment.
The PB processes are started automatically by the PXMCOM process when the
Pathway/XM environment is first started. The link control service (LCS) processes are
started automatically by their associated PATHMON processes along with the
distributed server classes under their control.
Transaction Queuing
As each LCS process receives transaction requests for its distributed server class, it
queues the requests in its transaction queue. It then requests authorization from the PB
process to start the server processes needed to service the queue. The LCS asks the PB
process for a process reservation—that is, a reservation for the use of a server process
for a predetermined amount of time. The length of time that the LCS process requests is
based on the current queue statistics. When this reservation is close to the expiration
time, the LCS either requests an extension or it allows the reservation to expire and then
closes the server process. (Closing the server process allows the server to stop itself.)
As the LCS queue for a server class increases, additional server processes are
automatically created in the processors designated in the logical node. The
configuration of the logical node defines a weight value for each processor based on the
percentage of processes it can support in the Pathway/XM environment. When new
server processes need to be started, this is done in parallel with the servicing of the
transaction queue by existing server processes. When the transaction queue cannot keep
all the existing server processes busy, the inactive server processes stop after their
reservation times have expired. Unused resources are thus freed and can be reallocated
as needed.
Individual server processes within a distributed server class are assigned to service
transaction requests based on their availability. If transactions are waiting in the queue,
then all server processes should be busy processing transactions. Only when a server
process completes its current transaction is it scheduled for a new one. Therefore, it is
likely that only one server is available at a time. When multiple servers are available, a
round-robin assignment mechanism is used based on the available processors.