The Harvester component of the WebLogic Diagnostic Framework (WLDF) gathers metrics from attributes on qualified MBeans that are instantiated in a running server. The Harvester can collect metrics from BEA WebLogic Server® MBeans and from custom MBeans.
The following sections describe harvesting and the Harvester configuration process:
Harvesting metrics is the process of gathering data that is useful for monitoring system state and performance. Metrics are exposed to WLDF as attributes on qualified MBeans. The Harvester gathers values from selected MBean attributes at a specified sampling rate. Therefore, you can track potentially fluctuating values over time.
Data must meet certain requirements in order to be harvestable, and it must meet further requirements in order to be harvested:
WLDFHarvesterRuntimeMBean provides the set of harvestable data and harvested data. The information returned by this MBean is a snapshot of a potentially changing state. For a description of the information about the data provided by the this MBean, see the description of the
You can use the Administration Console, the WebLogic Scripting Tool (
weblogic.WLST), or JMX to configure the harvester to collect and archive the metrics that the server MBeans and the custom MBeans contain.
You can configure the Harvester to harvest data from named MBean types, instances, and attributes. In all cases, the Harvester collects the values of attributes of MBean instances, as explained in Table 6-1.
All WebLogic Server runtime MBean types and attributes are known at startup. Therefore, when the Harvester configuration is loaded, the set of harvestable WebLogic Server entities is the same as the set of WebLogic Server runtime MBean types and attributes. As types are instantiated, those instances also become known and thus harvestable.
The set of harvestable custom MBean types is dynamic. A custom MBean must be instantiated before its type can be known. (The type does not exist until at least one instance is created.) Therefore, as custom MBeans are registered with and removed from the MBean server, the set of custom harvestable types grows and shrinks. This process of detecting a new type based on the registration of a new MBean is called type discovery.
When you configure the Harvester through the Administration Console, the Console provides a list of harvestable entities that can be configured. The list is always complete for WebLogic Server MBeans, but for custom MBeans, the list contains only the currently discovered types. Seein the Administration Console Online Help.
The Harvester is configured and metrics are collected in the scope of a diagnostic module targeted to one or more server instances.
Listing 6-1 shows Harvester configuration elements in a WLDF system resource descriptor file,
myWLDF.xml. This sample configuration harvests from the
WLDFHarvesterRuntimeMBean, and from a custom (non-WLS) MBean. The text following the listing explains each element in the listing.
<!-- ----- Other elements ----- -->
sample-period> element sets the sample period for the Harvester, in milliseconds. For example:
The sample period specifies the time between each cycle. For example, if the Harvester begins execution at time
T, and the sample period is
I, then the next harvest cycle begins at
I. If a cycle takes
A seconds to complete and if
I, then the next cycle begins at
A. If this occurs, the Harvester tries to start the next cycle sooner, to ensure that the average interval is
One or more
<harvested-type> elements determine the types of data to harvest. Each
<harvested-type> element specifies an MBean type from which metrics are to be collected. Optional sub-elements specify the instances and/or attributes to be collected for that type. Set these options as follows:
<harvested-instance>element specifies that metrics are to be collected only from the listed instances of the specified type. In general, an instance is specified by providing its JMX
ObjectNamein JMX canonical form.
<harvested-instance>is present, all instances that are present at the time of each harvest cycle are collected.
<harvested-attribute>element specifies that metrics are to be collected only for the listed attributes of the specified type. An attribute is specified by providing its name. The first character should be capitalized. For example, an attribute defined with getter method
<harvested-attribute>is present, all attributes defined for the type are collected.
The Harvester supports WebLogic Server MBeans and custom MBeans. WebLogic Server MBeans are those which come packaged as part of the WebLogic Server. Custom MBeans can be harvested as long as they are registered in the local runtime MBean server.
There is a difference in how WebLogic Server and customer types are specified. For WebLogic Server types, the type name is the name of the Java interface which defines that MBean. For example, the server runtime MBean's type name is
For custom MBeans, the Harvester follows these rules:
If neither of these conditions is satisfied (if the MBean is a
ModelMBean and there is no value for the MBean Descriptor field
DiagnosticTypeName) then the MBean can not be harvested.
WLDF attempts to validate configuration as soon as possible. Most configuration is validated at system startup and whenever a dynamic change is committed. However, due to limitations in JMX, custom MBeans cannot be validated until instances of those MBeans have been registered in the MBean server.
In Listing 6-2, the <harvested-type> element in the
.xml configuration file specifies that the
ServerRuntimeMBean is to be harvested. Because no
<harvested-instance> sub-element is present, all instances of the type will be collected. However, because there is always only one instance of the server runtime MBean, there is no need to provide a specific list of instances. And because there are no
<harvested-attribute> sub-elements present, all available attributes of the MBean are harvested.
In Listing 6-3, the <harvested-type> element in the
.xml configuration file specifies that the
WLDFHarvesterRuntimeMBean is to be harvested. As above, because there is only one WLDFHarvesterRuntimeMBean, there is no need to provide a specific list of instances. The sub-element
<harvested-attribute> specifies that only two of the available attributes of the WLDFHarvesterRuntimeMBean will be harvested:
In Listing 6-4, the <harvested-type> element in the
.xml configuration file specifies that a single instance of a custom MBean type is to be harvested. Because this is a custom MBean, the type name is the implementation class. In this example, the two
<harvested-instance> elements specify that only two instances of this type will be harvested. Each instance is specified using the canonical representation of its JMX
ObjectName. Because no instances of
<harvested-attribute> are specified, all attributes will be harvested.