6 IBM Enterprise Workload Manager
managed server layer understands each of the supported operating systems, gathering
resource usage and delay statistics known to the operating system.
A second role of the managed server layer is to gather relevant transaction-related statistics
from middleware applications. The application middleware implementations, such as
WebSphere Application Server, understand when a piece of work starts and stops, and the
middleware understands when a piece of work has been routed to another server for
processing, for example, when a Web server routes a servlet request to a WebSphere
Application Server.
The managed server layer dynamically constructs a server-level view describing relationships
between transaction segments known by the applications with resource consumption data
known by the operating system. A summary of this information is periodically sent to the
domain manager, where the information is gathered together from all the servers in the
management domain to form a global view.
An important aspect of the EWLM approach is that all data collection and aggregation
activities are driven by a common service level policy, called the EWLM
Domain Policy. This
policy is built by an administrator to describe the various business processes that the domain
supports and the performance objectives for each process. For example, a book store would
probably have a business transaction called “Add to shopping cartthat would have a
performance goal of perhaps a 1.5 second response time.
To permit the EWLM domain manager to construct an end-to-end view of each type of
business transaction, the processing segments performed by each participating middleware
instance must be correlated, meaning pieced together. For example, the Add to shopping
cart transaction would be received by a Web server, it could flow to a WebSphere
Application Server instance which might update a database. The transaction might even
check your credit limit by routing a sub-transaction to another server. The tricky part of this
correlation is to get all of the applications in the path of each transaction to cooperate, without
knowing that they are cooperating.
The final aspect of EWLM to introduce is the EWLM
Control Center, a browser-based
application server tailored to the needs of an EWLM administrator, analyst, and operator. This
is where all the EWLM concepts come together; where you can create a service level
and activate that policy on hundreds of servers with a single click. Reporting data is
then available to let you view performance from a business perspective. And if you need the
details, you can see the topology of servers and applications supporting each transaction
type and understand where the time was spent.
The information is organized in such a way that an administrator or analyst can easily
drill-down to what is relevant.
1.2.1 Domain manager
The domain manager is a software stack that you install and configure for your EWLM
environment. It consists of two operating system processes: one supports the Control Center
and one coordinates policy across the managed servers and aggregates performance
statistics. The size of the server that you install the domain manager on is dependent on the
number of managed servers and the Domain Policy complexity. See “Initial performance
considerations” on page 219 for more details.
The domain manager has a complete view of what’s going on in the domain. It keeps recent
historical data collected from the managed servers. The data can be displayed for as little as
one minute or up to an hour interval.

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