fix merge bug

* avoid using empty metric's value as input to max() and min()

2 files changed, 41 insertions, 4 deletions

diff --git a/simplemetrics/src/main/java/com/yahoo/metrics/simple/UntypedMetric.java b/simplemetrics/src/main/java/com/yahoo/metrics/simple/UntypedMetric.java
index 3a9f71b932c..f6762434275 100644
--- a/simplemetrics/src/main/java/com/yahoo/metrics/simple/UntypedMetric.java
+++ b/simplemetrics/src/main/java/com/yahoo/metrics/simple/UntypedMetric.java
@@ -74,12 +74,20 @@ public class UntypedMetric {
         if (outputFormat != other.outputFormat) {
             throw new IllegalArgumentException("Mismatching output formats: " + outputFormat + " and " + other.outputFormat + ".");
         }
-        count += other.count;
-        if (otherIsNewer) {
+        if (count > 0) {
+            if (other.count > 0) {
+                max = Math.max(other.max, max);
+                min = Math.min(other.min, min);
+                if (otherIsNewer) {
+                    current = other.current;
+                }
+            }
+        } else {
+            max = other.max;
+            min = other.min;
             current = other.current;
         }
-        max = Math.max(other.max, max);
-        min = Math.min(other.min, min);
+        count += other.count;
         sum += other.sum;
         if (histogram != null) {
             // some config scenarios may lead to differing histogram settings,
diff --git a/simplemetrics/src/test/java/com/yahoo/metrics/simple/BucketTest.java b/simplemetrics/src/test/java/com/yahoo/metrics/simple/BucketTest.java
index 927fea9ea0a..b33da4bd531 100644
--- a/simplemetrics/src/test/java/com/yahoo/metrics/simple/BucketTest.java
+++ b/simplemetrics/src/test/java/com/yahoo/metrics/simple/BucketTest.java
@@ -137,6 +137,35 @@ public class BucketTest {
         assertEquals(3, entry.getValue().getCount());
     }
 
+    @Test
+    public final void testMergeDifferentMetrics() {
+        bucket.put(new Sample(new Measurement(2), new Identifier("nalle", null), AssumedType.GAUGE));
+        Bucket otherNew = new Bucket();
+        otherNew.put(new Sample(new Measurement(3), new Identifier("other", null), AssumedType.GAUGE));
+        bucket.merge(otherNew, true);
+        Set<Entry<Identifier, UntypedMetric>> entries = bucket.entrySet();
+        assertEquals(2, entries.size());
+
+        Collection<Map.Entry<Point, UntypedMetric>> nalle_values = bucket.getValuesForMetric("nalle");
+        assertEquals(1, nalle_values.size());
+        Collection<Map.Entry<Point, UntypedMetric>> other_values = bucket.getValuesForMetric("other");
+        assertEquals(1, other_values.size());
+
+        UntypedMetric nalle_v = nalle_values.iterator().next().getValue();
+        assertEquals(1, nalle_v.getCount());
+        assertEquals(2, nalle_v.getSum(), 0.0);
+        assertEquals(2, nalle_v.getLast(), 0.0);
+        assertEquals(2, nalle_v.getMin(), 0.0);
+        assertEquals(2, nalle_v.getMax(), 0.0);
+
+        UntypedMetric other_v = other_values.iterator().next().getValue();
+        assertEquals(1, other_v.getCount());
+        assertEquals(3, other_v.getSum(), 0.0);
+        assertEquals(3, other_v.getLast(), 0.0);
+        assertEquals(3, other_v.getMax(), 0.0);
+        assertEquals(3, other_v.getMin(), 0.0);
+    }
+
     private static class CheckThatItWasLogged extends Handler {
         final boolean[] loggingMarker;