You can configure vertical stacking to enable the application
placement controller to start more than one instance of the dynamic
cluster to improve bottleneck conditions within an application.
Before you begin
- Vertical stacking is supported on the z/OS® operating system, but the WebSphere® Application Server for z/OS multiple servant feature is
the preferred alternative. Consider using vertical stacking for application
servers on the z/OS operating
systems only for application servers that host applications that are
constrained to run in a single servant application server.
- To use vertical stacking, the nodes in your dynamic cluster must
be at the same product version as the deployment manager, or at a
later version. Nodes that are at an earlier release than the deployment
manager cannot start multiple server instances on the same node.
- Vertical stacking can occur only on nodes that have complete life
cycle management. You cannot configure vertical stacking for dynamic
clusters that have manually defined cluster members.
About this task
Use vertical stacking to improve bottleneck conditions in
your application. With vertical stacking, multiple server instances
can start on a node. By configuring multiple server instances, you
can use all the power that is available on the nodes when a large
workload exists for the application.
Procedure
- Determine whether your application has an internal bottleneck
by profiling the application.
The application placement
controller assumes that the only resource bottleneck that an application
might have is either in the processor or in memory. Otherwise, the
application might have an internal bottleneck.
- Run an instance of the application on each node.
- Increase the load for the application.
- Analyze the runtime reports, the throughput curves and
processor utilization charts for the nodes that are running the application.
Click .
If the throughput curve saturates while increasing the
load, but the processor utilization remains well under 100%, the application
might have an internal bottleneck. Configure vertical stacking to
improve these bottleneck conditions. If the server instances are able
to reach processor utilization near 100%, do not enable vertical stacking.
- Determine the appropriate stacking number. The stacking
number is the number of application servers for a cluster that are
needed to use all the power of a node.
For more information
about determining a stacking number, read about determining the stacking
number for a dynamic cluster.
- Enable vertical stacking and the stacking number.
If
your dynamic cluster is deployed to a node group that has homogeneous
nodes, you can configure the stacking number one time in the administrative
console. If your dynamic cluster is deployed to a node group that
has heterogeneous nodes, you must configure the stacking number by
specifying custom properties.
- For more information about enabling vertical stacking for
a dynamic cluster that is on homogenous nodes, read about configuring
a dynamic cluster with homogeneous nodes to support vertical stacking.
- For more information about enabling vertical stacking for
a dynamic cluster that is on heterogeneous nodes, read about configuring
a dynamic cluster with heterogeneous nodes to support vertical stacking.
Results
When a large workload exists, the application placement controller
can fully use the power of the nodes by starting multiple cluster
instances on each node. The general formula to determine the percentage
of the processor that is used by each instance on a node is 100%/maximum_number_of_stacked_instances
.
For example, if three instances are stacked, then workload is throttled
to prevent any one of these instances from using more than 33% of
the processor.
What to do next
Tune and monitor your application placement configuration.