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Date: Sun, 25 Nov 2012 20:34:58 +0000 (UTC)
From: "Mostafa Elhemali (JIRA)" <jira@apache.org>
To: common-dev@hadoop.apache.org
Message-ID: <332134880.21535.1353875698720.JavaMail.jiratomcat@arcas>
Subject: [jira] [Created] (HADOOP-9090) Refactor MetricsSystemImpl to allow
 for an on-demand publish system
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Mostafa Elhemali created HADOOP-9090:
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             Summary: Refactor MetricsSystemImpl to allow for an on-demand publish system
                 Key: HADOOP-9090
                 URL: https://issues.apache.org/jira/browse/HADOOP-9090
             Project: Hadoop Common
          Issue Type: New Feature
          Components: metrics
            Reporter: Mostafa Elhemali
            Priority: Minor
         Attachments: HADOOP-9090.patch

We have a need to publish metrics out of some short-living processes, which is not really well-suited to the current metrics system implementation which periodically publishes metrics asynchronously (a behavior that works great for long-living processes). Of course I could write my own metrics system, but it seems like such a waste to rewrite all the awesome code currently in the MetricsSystemImpl and supporting classes.

The way I'm proposing to solve this is to:
1. Refactor the MetricsSystemImpl class into an abstract base MetricsSystemImpl class (common configuration and other code) and a concrete PeriodicPublishMetricsSystemImpl class (timer thread).
2. Refactor the MetricsSinkAdapter class into an abstract base MetricsSinkAdapter class (common configuration and other code) and a concrete AsyncMetricsSinkAdapter class (asynchronous publishing using the SinkQueue).
3. Derive a new simple class OnDemandPublishMetricsSystemImpl from MetricsSystemImpl, that just exposes a synchronous publish() method to do all the work.
4. Derive a SyncMetricsSinkAdapter class from MetricsSinkAdapter to just synchronously push metrics to the underlying sink.

Does that sound reasonable? I'll attach the patch with all this coded up and simple tests (could use some polish I guess, but wanted to get everyone's opinion first). Notice that this is somewhat of a breaking change since MetricsSystemImpl is public (although it's marked with InterfaceAudience.Private); if the breaking change is a problem I could just rename the refactored classes so that PeriodicPublishMetricsSystemImpl is still called MetricsSystemImpl (and MetricsSystemImpl -> BaseMetricsSystemImpl).

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