only call refresh if its needed, so we check outside of the readLock when async refreshing

modules/elasticsearch/src/main/java/org/elasticsearch/index/engine/Engine.java

@@ -66,6 +66,11 @@ public interface Engine extends IndexShardComponent, CloseableComponent {
 
     Searcher searcher() throws EngineException;
 
+    /**
+     * Returns <tt>true</tt> if a refresh is really needed.
+     */
+    boolean refreshNeeded();
+
     /**
      * Refreshes the engine for new search operations to reflect the latest
      * changes. Pass <tt>true</tt> if the refresh operation should include

modules/elasticsearch/src/main/java/org/elasticsearch/index/engine/robin/RobinEngine.java

@@ -588,6 +588,10 @@ public class RobinEngine extends AbstractIndexShardComponent implements Engine,
         }
     }
 
+    @Override public boolean refreshNeeded() {
+        return dirty;
+    }
+
     @Override public void refresh(Refresh refresh) throws EngineException {
         if (indexWriter == null) {
             throw new EngineClosedException(shardId);

modules/elasticsearch/src/main/java/org/elasticsearch/index/shard/service/InternalIndexShard.java

@@ -607,7 +607,9 @@ public class InternalIndexShard extends AbstractIndexShardComponent implements I
     private class EngineRefresher implements Runnable {
         @Override public void run() {
             try {
-                engine.refresh(new Engine.Refresh(false));
+                if (engine.refreshNeeded()) {
+                    engine.refresh(new Engine.Refresh(false));
+                }
             } catch (EngineClosedException e) {
                 // we are being closed, ignore
             } catch (RefreshFailedEngineException e) {