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https://issues.apache.org/jira/browse/HADOOP-3772?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12614025#action_12614025
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Ari Rabkin commented on HADOOP-3772:
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I think the right way to do this is to add several Instrumentation interfaces,
such as JobInstrumentation, NameNodeInstrumentation, DNInstrumentation. These
classes would have one method per instrumentation point; and all the metrics
computation, causal logging, Chukwa integration, and so forth would be hidden
in implementations. Much of Metrics, such as the visible methods of
JobTrackerMetrics and much of the MetricsContextFactory, can be reused. Other
parts can be encapsulated.
We'll probably start with TaskTrackerMetrics. We can then build an
implementation of TaskTrackerInstrumentation that notifies Chukwa to pick up
the task's stdout and stderr. This gives us the hooks to do log and console out
harvesting for Chukwa, which lets us close HADOOP-2206, and probably
HADOOP-1199.
> Proposed hadoop instrumentation API
> -----------------------------------
>
> Key: HADOOP-3772
> URL: https://issues.apache.org/jira/browse/HADOOP-3772
> Project: Hadoop Core
> Issue Type: Improvement
> Components: metrics
> Reporter: Ari Rabkin
>
> We want to evolve the Hadoop metrics subsystem into a more generic
> Instrumentation facility. The ultimate goal is to add structured logging to
> Hadoop, with causal tags, a la X-trace. The existing metrics framework is
> not quite suitable for our needs, since the implementation and interface are
> tightly coupled. There's no way to use the metrics instrumentation points for
> anything other than metricss, and there's no way for a metrics context to
> find out what event just happened.
> We want to tease apart the generic notion of hookable instrumentation points,
> from the specifics of the information recording. The latter ought to be
> pluggable at run-time.
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