PMI data organization

Performance Monitoring Infrastructure (PMI) provides server-side monitoring and a client-side API to retrieve performance data. PMI maintains statistical data within the entire WebSphere® Application Server domain, including multiple nodes and servers. Each node can contain one or more WebSphere Application Server. Each server organizes PMI data into modules and submodules.

Tivoli Performance Viewer is a thin client integrated into the WebSphere Application Server administrative console. It provides a simple viewer for the performance data provided by Performance Monitoring Infrastructure (PMI), and allows users to view and manipulate the data for counters. A particular counter type can appear in several modules. For example, both the servlet and enterprise bean modules have a response time counter. In addition, a counter type can have multiple instances within a module. In the previous figure, both the Enterprise beans module and Bean1 have an Avg Method RT counter.

Counters are enabled at the module level and can be enabled or disabled for elements within the module. For example, in the figure, if the enterprise beans module is enabled, its Avg Method RT counter is enabled by default. However, you can then disable the Avg Method RT counter even when the rest of the module counters are enabled. You can also, if desired, disable the Avg Method RT counter for Bean1, but the aggregate response time reported for the whole module no longer includes Bean1 data.

As part of a fine-grained control feature, WebSphere Application Server provides statistic sets which are pre-defined, fixed server-side sets, based on the PMI statistic usage scenarios. The PMI specification levels include: none, basic, extended, all, or custom. If you choose none, all PMI modules are disabled. Choosing basic provides the J2EE and the essential set of statistics to give you a basic level of monitoring. Selecting extended gives you the basic level of monitoring plus Work Load Monitor, Performance Advisor, and Tivoli resource models for a more robust monitoring set. Choosing all enables all statistics. Choosing custom gives you fine-grained control to enable or disable statistics individually.

There are only two states for a statistic: enabled or disabled. To provide an option to enable synchronized updates, WebSphere Application Server, provides a configuration parameter, synchronizedUpdate, at the PMI service level. When this attribute is true, all the statistic updates are synchronized. By default, the synchronizedUpdate parameter is set to false. You can select the Use sequential counter updates check box in the administrative console to enable synchronized updates.

Data collection can affect performance of the application server. The impact depends on the number of counters enabled, the type of counters enabled and the monitoring level set for the counters.

You can access PMI data through the getStatsObject and the getStatsArray method in the PerfMBean. You need to pass the MBean ObjectName(s) to the PerfMBean.

To use the AdminClient API to query the MBean ObjectName for each MBean type. You can either query all the MBeans and then match the MBean type or use the query String for the type only: String query = "WebSphere:type=mytype,node=mynode,server=myserver,*";

Set the mytype, mynode, and myserver values accordingly. You get a Set value when you call the AdminClient class to query MBean ObjectNames. This response means that you can get multiple ObjectNames.

In the previous example, the MBean types with a star (*) mean that there can be multiple ObjectNames in a server for the same MBean type. In this case, the ObjectNames can be identified by both type and name (but mbeanIdentifier is the real UID for MBeans). However, the MBean names are not predefined. They are decided at run time based on the applications and resources. When you get multiple ObjectNames, you can construct an array of ObjectNames that you are interested in. Then you can pass the ObjectNames to PerfMBean to get PMI data. You have the recursive and non-recursive options. The recursive option returns Stats and sub-stats objects in a tree structure while the non-recursive option returns a Stats object for that MBean only. More programming information can be found in Developing your own monitoring applications.