Index: oak-core/src/main/java/org/apache/jackrabbit/oak/query/QueryImpl.java
===================================================================
--- oak-core/src/main/java/org/apache/jackrabbit/oak/query/QueryImpl.java	(revision 1842619)
+++ oak-core/src/main/java/org/apache/jackrabbit/oak/query/QueryImpl.java	(working copy)
@@ -1042,6 +1042,14 @@
             if (cost < 0) {
                 LOG.error("cost below 0 for " + indexName + " is " + cost);
             }
+
+            if (LOG.isDebugEnabled()) {
+                if (Math.abs(bestCost - cost) <= 0.1) {
+                    LOG.debug("index {} and {} have similar costs {} and {} for query {} - check query explanation / index definitions",
+                            index, bestIndex, cost, bestCost, filter.toString());
+                }
+            }
+
             if (cost < bestCost) {
                 bestCost = cost;
                 bestIndex = index;
Index: oak-search/src/main/java/org/apache/jackrabbit/oak/plugins/index/search/FieldNames.java
===================================================================
--- oak-search/src/main/java/org/apache/jackrabbit/oak/plugins/index/search/FieldNames.java	(revision 1842619)
+++ oak-search/src/main/java/org/apache/jackrabbit/oak/plugins/index/search/FieldNames.java	(working copy)
@@ -16,7 +16,6 @@
  */
 package org.apache.jackrabbit.oak.plugins.index.search;
 
-import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashSet;
 import java.util.Set;