Merge pull request #756 from metamx/dimdim-comments

add some comments about string interning

processing/src/main/java/io/druid/segment/incremental/IncrementalIndex.java

@@ -673,6 +673,10 @@ public class IncrementalIndex implements Iterable<Row>
       falseIdsReverse = biMap.inverse();
     }
 
+    /**
+     * Returns the interned String value to allow fast comparisons using `==` instead of `.equals()`
+     * @see io.druid.segment.incremental.IncrementalIndexStorageAdapter.EntryHolderValueMatcherFactory#makeValueMatcher(String, String)
+     */
     public String get(String value)
     {
       return value == null ? null : poorMansInterning.get(value);

processing/src/main/java/io/druid/segment/incremental/IncrementalIndexStorageAdapter.java

@@ -528,6 +528,10 @@ public class IncrementalIndexStorageAdapter implements StorageAdapter
           }
 
           for (String dimVal : dims[dimIndex]) {
+            /**
+             * using == here instead of .equals() to speed up lookups made possible by
+             * {@link io.druid.segment.incremental.IncrementalIndex.DimDim#poorMansInterning}
+             */
             if (id == dimVal) {
               return true;
             }