From a9fd4ab40c744b810ce00fae808f9f7e668a8332 Mon Sep 17 00:00:00 2001
From: Jason Jackson <jackson@twitter.com>
Date: Thu, 6 Dec 2012 13:55:06 -0800
Subject: [PATCH] MeanReducer no longer divides by zero.

---
 src/clj/backtype/storm/daemon/executor.clj         | 5 ++++-
 src/jvm/backtype/storm/metric/api/MeanReducer.java | 6 +++++-
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/src/clj/backtype/storm/daemon/executor.clj b/src/clj/backtype/storm/daemon/executor.clj
index 95aff4345..2e176bcd2 100644
--- a/src/clj/backtype/storm/daemon/executor.clj
+++ b/src/clj/backtype/storm/daemon/executor.clj
@@ -269,7 +269,10 @@
                              interval)
                   data-points (->> name->imetric
                                    (map (fn [[name imetric]]
-                                          (IMetricsConsumer$DataPoint. name (.getValueAndReset ^IMetric imetric))))
+                                          (let [value (.getValueAndReset ^IMetric imetric)]
+                                            (if value
+                                              (IMetricsConsumer$DataPoint. name value)))))
+                                   (filter identity)
                                    (into []))]]
       (if (seq data-points)
         (task/send-unanchored task-data Constants/METRICS_STREAM_ID [task-info data-points])))))
diff --git a/src/jvm/backtype/storm/metric/api/MeanReducer.java b/src/jvm/backtype/storm/metric/api/MeanReducer.java
index 2133dd9f3..38f627507 100644
--- a/src/jvm/backtype/storm/metric/api/MeanReducer.java
+++ b/src/jvm/backtype/storm/metric/api/MeanReducer.java
@@ -29,6 +29,10 @@ public MeanReducerState reduce(MeanReducerState acc, Object input) {
     }
 
     public Object extractResult(MeanReducerState acc) {
-        return new Double(acc.sum / (double)acc.count);
+        if(acc.count > 0) {
+            return new Double(acc.sum / (double)acc.count);
+        } else {
+            return null;
+        }
     }
 }