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https://issues.apache.org/jira/browse/HBASE-18409?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16129837#comment-16129837
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Josh Elser commented on HBASE-18409:
------------------------------------

Hi, [~macmaster]! Mighty nice patch you've put together here.

Isolating the metrics aggregation behind the new hbase-metrics API is a great 
idea, IMO.

{code}
+  /////// Other Bases ///////
...
+  /////// Other Bases ///////
{code}

Maybe tone these down? :) Just a leading comment character would be sufficient

{code}
+    this.regionStats = new HashMap<String, RegionStats>();
+    this.cacheDroppingExceptions = new HashMap<String, MutableFastCounter>();
{code}

You can omit the types on the RHS. The bare diamond operator is sufficient.

{code}
+  @VisibleForTesting
+  protected final Map<String, RegionStats> regionStats;
+  @VisibleForTesting
+  protected final Map<String, MutableFastCounter> cacheDroppingExceptions;
{code}

These were ConcurrentHashMaps above. Are we sure that we don't need the 
concurrency-safety now?

{code}
+  private final String POOL_EXECUTOR_ACTIVE_KEY = "executorPoolActiveThreads";
+  private final String POOL_EXECUTOR_ACTIVE_DESC = "number of active threads 
in the executor pool";
+  private final String POOL_META_ACTIVE_KEY = "metaPoolActiveThreads";
+  private final String POOL_META_ACTIVE_DESC = "number of active threads in 
the meta pool";
{code}

These are net-new metrics? Should they be spun out into a different JIRA issue 
(we try to limit one "thing" per JIRA issue).

FYI [~stack], I think you had done a review on the hbase-metrics API patch when 
Enis brought it in. Thought you might be interested in this one too.

> Migrate Client Metrics from codahale to hbase-metrics
> -----------------------------------------------------
>
>                 Key: HBASE-18409
>                 URL: https://issues.apache.org/jira/browse/HBASE-18409
>             Project: HBase
>          Issue Type: Improvement
>          Components: Client, java, metrics
>    Affects Versions: 3.0.0
>            Reporter: Ronald Macmaster
>              Labels: newbie
>             Fix For: 3.0.0
>
>         Attachments: 
> 0001-HBASE-18409-MetricsConnection-client-metrics-migration.patch, 
> 0002-HBASE-18409-MetricsConnection-client-metrics-migrati.patch
>
>   Original Estimate: 168h
>  Remaining Estimate: 168h
>
> Currently, the metrics for hbase-client are tailored for reporting via a 
> client-side JMX server.
> The MetricsConnection handles the metrics management and reporting via the 
> metrics platform from codahale. 
> This approach worked well for hbase-1.3.1 when the metrics platform was still 
> relatively young, but it could be improved by using the new 
> hbase-metrics-api. 
> Now that we have an actual hbase-metrics-api that master, regionserver, 
> zookeeper, and other daemons use, it would be good to also allow the client 
> to leverage the metrics-api. 
> Then, the client could also report its metrics via Hadoop's metrics2 if 
> desired or through another platform that utilizes the hbase-metrics-api. 
> If left alone, client metrics will continue to be only barely visible through 
> a client-side JMX server.
> The migration to the new metrics-api could be done by simply changing the 
> Metrics data types from codahale types to hbase-metrics types without 
> changing the metrics signatures of MetricsConnection unless completely 
> necessary. 
> The codahale MetricsRegistry would also have to be exchanged for a 
> hbase-metrics MetricsRegistry. 
> I found this to be a necessary change after attempting to implement my own 
> Reporter to use within the MetricsConnection class.
> I was attempting to create a HadoopMetrics2Reporter that extends the codahale 
> ScheduledReporter and reports the MetricsConnection metrics to Hadoop's 
> metrics2 system. 
> The already existing infrastructure in the hbase-metrics and 
> hbase-metrics-api projects could be easily leveraged for a cleaner solution.
> If completed successfully, users could instead access their client-side 
> metrics through the hbase-metrics-api. 



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