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From alek...@apache.org
Subject cassandra git commit: Make EstimatedHistogram#percentile() use ceil instead of floor
Date Wed, 04 Mar 2015 05:02:30 GMT
Repository: cassandra
Updated Branches:
  refs/heads/cassandra-2.1 0127b6963 -> d4e37869b


Make EstimatedHistogram#percentile() use ceil instead of floor

patch by Carl Yeksigian; reviewed by Chris Lohfink for CASSANDRA-8883


Project: http://git-wip-us.apache.org/repos/asf/cassandra/repo
Commit: http://git-wip-us.apache.org/repos/asf/cassandra/commit/d4e37869
Tree: http://git-wip-us.apache.org/repos/asf/cassandra/tree/d4e37869
Diff: http://git-wip-us.apache.org/repos/asf/cassandra/diff/d4e37869

Branch: refs/heads/cassandra-2.1
Commit: d4e37869b1465b231ada7554fb7a6d5ccf43f493
Parents: 0127b69
Author: Carl Yeksigian <carl@apache.org>
Authored: Tue Mar 3 13:54:51 2015 -0500
Committer: Aleksey Yeschenko <aleksey@apache.org>
Committed: Tue Mar 3 21:01:14 2015 -0800

----------------------------------------------------------------------
 CHANGES.txt                                     |  1 +
 .../cassandra/utils/EstimatedHistogram.java     |  2 +-
 .../cassandra/utils/EstimatedHistogramTest.java | 52 ++++++++++++++++----
 3 files changed, 44 insertions(+), 11 deletions(-)
----------------------------------------------------------------------


http://git-wip-us.apache.org/repos/asf/cassandra/blob/d4e37869/CHANGES.txt
----------------------------------------------------------------------
diff --git a/CHANGES.txt b/CHANGES.txt
index 7ce6200..748acf8 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -1,4 +1,5 @@
 2.1.4
+ * Make EstimatedHistogram#percentile() use ceil instead of floor (CASSANDRA-8883)
  * Fix top partitions reporting wrong cardinality (CASSANDRA-8834)
  * Fix rare NPE in KeyCacheSerializer (CASSANDRA-8067)
  * Pick sstables for validation as late as possible inc repairs (CASSANDRA-8366)

http://git-wip-us.apache.org/repos/asf/cassandra/blob/d4e37869/src/java/org/apache/cassandra/utils/EstimatedHistogram.java
----------------------------------------------------------------------
diff --git a/src/java/org/apache/cassandra/utils/EstimatedHistogram.java b/src/java/org/apache/cassandra/utils/EstimatedHistogram.java
index 196a3b9..a5c51c8 100644
--- a/src/java/org/apache/cassandra/utils/EstimatedHistogram.java
+++ b/src/java/org/apache/cassandra/utils/EstimatedHistogram.java
@@ -178,7 +178,7 @@ public class EstimatedHistogram
         if (buckets.get(lastBucket) > 0)
             throw new IllegalStateException("Unable to compute when histogram overflowed");
 
-        long pcount = (long) Math.floor(count() * percentile);
+        long pcount = (long) Math.ceil(count() * percentile);
         if (pcount == 0)
             return 0;
 

http://git-wip-us.apache.org/repos/asf/cassandra/blob/d4e37869/test/unit/org/apache/cassandra/utils/EstimatedHistogramTest.java
----------------------------------------------------------------------
diff --git a/test/unit/org/apache/cassandra/utils/EstimatedHistogramTest.java b/test/unit/org/apache/cassandra/utils/EstimatedHistogramTest.java
index bbfd1c7..eebaa25 100644
--- a/test/unit/org/apache/cassandra/utils/EstimatedHistogramTest.java
+++ b/test/unit/org/apache/cassandra/utils/EstimatedHistogramTest.java
@@ -75,17 +75,49 @@ public class EstimatedHistogramTest
     @Test
     public void testPercentile()
     {
-        EstimatedHistogram histogram = new EstimatedHistogram();
-        // percentile of empty histogram is 0
-        assertEquals(0, histogram.percentile(0.99));
+        {
+            EstimatedHistogram histogram = new EstimatedHistogram();
+            // percentile of empty histogram is 0
+            assertEquals(0, histogram.percentile(0.99));
 
-        histogram.add(1);
-        // percentile of histogram with just one value will return 0 except 100th
-        assertEquals(0, histogram.percentile(0.99));
-        assertEquals(1, histogram.percentile(1.00));
+            histogram.add(1);
+            // percentile of a histogram with one element should be that element
+            assertEquals(1, histogram.percentile(0.99));
+
+            histogram.add(10);
+            assertEquals(10, histogram.percentile(0.99));
+        }
+
+        {
+            EstimatedHistogram histogram = new EstimatedHistogram();
+
+            histogram.add(1);
+            histogram.add(2);
+            histogram.add(3);
+            histogram.add(4);
+            histogram.add(5);
+
+            assertEquals(0, histogram.percentile(0.00));
+            assertEquals(3, histogram.percentile(0.50));
+            assertEquals(3, histogram.percentile(0.60));
+            assertEquals(5, histogram.percentile(1.00));
+        }
+
+        {
+            EstimatedHistogram histogram = new EstimatedHistogram();
+
+            for (int i = 11; i <= 20; i++)
+                histogram.add(i);
 
-        histogram.add(10);
-        assertEquals(1, histogram.percentile(0.99));
-        assertEquals(10, histogram.percentile(1.00));
+            // Right now the histogram looks like:
+            //    10   12   14   17   20
+            //     0    2    2    3    3
+            // %:  0   20   40   70  100
+            assertEquals(12, histogram.percentile(0.01));
+            assertEquals(14, histogram.percentile(0.30));
+            assertEquals(17, histogram.percentile(0.50));
+            assertEquals(17, histogram.percentile(0.60));
+            assertEquals(20, histogram.percentile(0.80));
+        }
     }
 }


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