diff --git a/collector/src/main/java/com/navercorp/pinpoint/collector/dao/hbase/statistics/RowKeyMerge.java b/collector/src/main/java/com/navercorp/pinpoint/collector/dao/hbase/statistics/RowKeyMerge.java
index e70d9c46c..2955699d4 100644
--- a/collector/src/main/java/com/navercorp/pinpoint/collector/dao/hbase/statistics/RowKeyMerge.java
+++ b/collector/src/main/java/com/navercorp/pinpoint/collector/dao/hbase/statistics/RowKeyMerge.java
@@ -58,8 +58,10 @@ public class RowKeyMerge {
         RowKey rowKey = rowKeyEntry.getKey();
         byte[] key = null;
         if(rowKeyDistributorByHashPrefix == null) {
+            // backward compatibility.
             key = rowKey.getRowKey();
         } else {
+            // distributed key.
             key = rowKeyDistributorByHashPrefix.getDistributedKey(rowKey.getRowKey());
         }
         final Increment increment = new Increment(key);