HBASE-11786 Document web UI for tracking time spent in coprocessors (Misty Stanley-Jones)

src/main/docbkx/cp.xml

@@ -401,6 +401,30 @@ coprocessors=[AggregateImplementation]
 0 dead servers      </computeroutput>
     </screen>
   </section>
+  <section>
+    <title>Monitor Time Spent in Coprocessors</title>
+    <para>HBase 0.98.5 introduced the ability to monitor some statistics relating to the amount of
+      time spent executing a given coprocessor. You can see these statistics via the HBase Metrics
+      framework (see <xref linkend="hbase_metrics"/> or the Web UI for a given Region Server, via
+      the <guilabel>Coprocessor Metrics</guilabel> tab. These statistics are valuable for debugging
+      and benchmarking the performance impact of a given coprocessor on your cluster. Tracked
+      statistics include min, max, average, and 90th, 95th, and 99th percentile. All times are shown
+      in milliseconds. The statistics are calculated over coprocessor
+      execution samples recorded during the reporting interval, which is 10 seconds by default. The
+      metrics sampling rate as described in <xref linkend="hbase_metrics" />.</para>
+    <figure>
+      <title>Coprocessor Metrics UI</title>
+      <mediaobject>
+        <imageobject>
+          <imagedata fileref="coprocessor_stats.png" width="100%"/>
+        </imageobject>
+        <textobject>
+          <para>The Coprocessor Metrics UI shows statistics about time spent executing a given
+            coprocessor, including min, max, average, and 90th, 95th, and 99th percentile.</para>
+        </textobject>
+      </mediaobject>
+    </figure>
+  </section>
   <section>
     <title>Status of Coprocessors in HBase</title>
     <para> Coprocessors and the coprocessor framework are evolving rapidly and work is ongoing on