com.bigdata.ganglia

Class GangliaRequestMessage

java.lang.Object

com.bigdata.ganglia.AbstractGangliaMessage

com.bigdata.ganglia.GangliaRequestMessage

All Implemented Interfaces:

IGangliaMessage, IGangliaRequestMessage

public class GangliaRequestMessage
extends AbstractGangliaMessage
implements IGangliaRequestMessage

A ganglia request for a metric.

Ganglia sends out request messages when a service wants to obtain fresh metrics. The gmond instances handle the request by clearing the timestamp associated with the metric. This causes the metric to be retransmitted soon thereafter (a ZERO (0) timestamp is interpreted as the metric having never been transmitted).

In order to prevent multicast storms, a service will conditionally clear the timestamp associated with a metric if it has been running for at least some minimum period of time (e.g., 10 minutes).

In order to generate request messages, a service needs to notice the first time any given metric name is declared (including metrics which it is self-reporting) and then multicast a request for that metric in order to obtain its value from all participating ganglia services. There is no means for a service to request a metric which it is neither self-reported nor observed.

It appears that ganglia actually tracks the age of metric groups as well as individual metrics and will reset the timestamp on the group if a request is received for any metric in that group.

The request record itself does not have any additional fields. It is just the metric_id header with the appropriate byte code for the record type.

Constructor Summary

Constructors

Constructor and Description
GangliaRequestMessage(String hostName, String metricName, boolean spoof)

Method Summary

Methods

Modifier and Type	Method and Description
boolean	equals(Object o)
int	hashCode()
boolean	isMetricMetadata() Return true iff this message contains the metadata for a metric (the metric declaration).
boolean	isMetricRequest() Return true iff this message is a request for a metric.
boolean	isMetricValue() Return true if this message represents a metric value.
String	toString()

Methods inherited from class com.bigdata.ganglia.AbstractGangliaMessage

getHostName, getMetricName, getRecordType, isSpoof

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface com.bigdata.ganglia.IGangliaMessage

getHostName, getMetricName, getRecordType, isSpoof

Constructor Detail

GangliaRequestMessage

public GangliaRequestMessage(String hostName,
                     String metricName,
                     boolean spoof)

Method Detail

isMetricValue

public boolean isMetricValue()

Description copied from interface: IGangliaMessage

Return true if this message represents a metric value.

Specified by:

isMetricValue in interface IGangliaMessage

isMetricRequest

public boolean isMetricRequest()

Description copied from interface: IGangliaMessage

Return true iff this message is a request for a metric.

Specified by:

isMetricRequest in interface IGangliaMessage

See Also:

GangliaMessageTypeEnum.REQUEST

isMetricMetadata

public boolean isMetricMetadata()

Description copied from interface: IGangliaMessage

Return true iff this message contains the metadata for a metric (the metric declaration).

Specified by:

isMetricMetadata in interface IGangliaMessage

See Also:

GangliaMessageTypeEnum.METADATA

toString

public String toString()

Overrides:

toString in class Object

equals

public boolean equals(Object o)

Specified by:

equals in class AbstractGangliaMessage

hashCode

public int hashCode()

Specified by:

hashCode in class AbstractGangliaMessage