diff --git a/modules/elasticsearch/src/main/java/org/elasticsearch/index/engine/Engine.java b/modules/elasticsearch/src/main/java/org/elasticsearch/index/engine/Engine.java
index 4cbd366f86d..4b551f8c1e7 100644
--- a/modules/elasticsearch/src/main/java/org/elasticsearch/index/engine/Engine.java
+++ b/modules/elasticsearch/src/main/java/org/elasticsearch/index/engine/Engine.java
@@ -69,6 +69,13 @@ public interface Engine extends IndexShardComponent, CloseableComponent {
      */
     boolean refreshNeeded();
 
+    /**
+     * Returns <tt>true</tt> if a possible merge is really needed.
+     */
+    boolean possibleMergeNeeded();
+
+    void maybeMerge() throws EngineException;
+
     /**
      * Refreshes the engine for new search operations to reflect the latest
      * changes. Pass <tt>true</tt> if the refresh operation should include
@@ -131,10 +138,21 @@ public interface Engine extends IndexShardComponent, CloseableComponent {
 
         private final boolean waitForOperations;
 
+        private boolean force = false;
+
         public Refresh(boolean waitForOperations) {
             this.waitForOperations = waitForOperations;
         }
 
+        public Refresh force(boolean force) {
+            this.force = force;
+            return this;
+        }
+
+        public boolean force() {
+            return this.force;
+        }
+
         public boolean waitForOperations() {
             return waitForOperations;
         }
diff --git a/modules/elasticsearch/src/main/java/org/elasticsearch/index/engine/robin/RobinEngine.java b/modules/elasticsearch/src/main/java/org/elasticsearch/index/engine/robin/RobinEngine.java
index 19440398eb1..8a0c5342674 100644
--- a/modules/elasticsearch/src/main/java/org/elasticsearch/index/engine/robin/RobinEngine.java
+++ b/modules/elasticsearch/src/main/java/org/elasticsearch/index/engine/robin/RobinEngine.java
@@ -113,6 +113,8 @@ public class RobinEngine extends AbstractIndexShardComponent implements Engine,
     // flag indicating if a dirty operation has occurred since the last refresh
     private volatile boolean dirty = false;
 
+    private volatile boolean possibleMergeNeeded = false;
+
     private volatile int disableFlushCounter = 0;
 
     // indexing searcher is initialized
@@ -228,6 +230,7 @@ public class RobinEngine extends AbstractIndexShardComponent implements Engine,
             }
             innerCreate(create, writer);
             dirty = true;
+            possibleMergeNeeded = true;
             if (create.refresh()) {
                 refresh(new Refresh(false));
             }
@@ -318,6 +321,7 @@ public class RobinEngine extends AbstractIndexShardComponent implements Engine,
 
             innerIndex(index, writer);
             dirty = true;
+            possibleMergeNeeded = true;
             if (index.refresh()) {
                 refresh(new Refresh(false));
             }
@@ -402,6 +406,7 @@ public class RobinEngine extends AbstractIndexShardComponent implements Engine,
             }
             innerDelete(delete, writer);
             dirty = true;
+            possibleMergeNeeded = true;
             if (delete.refresh()) {
                 refresh(new Refresh(false));
             }
@@ -485,6 +490,7 @@ public class RobinEngine extends AbstractIndexShardComponent implements Engine,
             writer.deleteDocuments(delete.query());
             translog.add(new Translog.DeleteByQuery(delete));
             dirty = true;
+            possibleMergeNeeded = true;
         } catch (IOException e) {
             throw new DeleteByQueryFailedEngineException(shardId, delete, e);
         } finally {
@@ -521,6 +527,10 @@ public class RobinEngine extends AbstractIndexShardComponent implements Engine,
         return dirty;
     }
 
+    @Override public boolean possibleMergeNeeded() {
+        return this.possibleMergeNeeded;
+    }
+
     @Override public void refresh(Refresh refresh) throws EngineException {
         if (indexWriter == null) {
             throw new EngineClosedException(shardId);
@@ -535,7 +545,7 @@ public class RobinEngine extends AbstractIndexShardComponent implements Engine,
                 throw new EngineClosedException(shardId);
             }
             try {
-                if (dirty) {
+                if (dirty || refresh.force()) {
                     // we eagerly set dirty to false so we won't miss refresh requests
                     dirty = false;
                     AcquirableResource<ReaderSearcherHolder> current = nrtResource;
@@ -586,6 +596,10 @@ public class RobinEngine extends AbstractIndexShardComponent implements Engine,
             if (disableFlushCounter > 0) {
                 throw new FlushNotAllowedEngineException(shardId, "Recovery is in progress, flush is not allowed");
             }
+            if (indexingSearcher.get() != null) {
+                indexingSearcher.get().release();
+                indexingSearcher.set(null);
+            }
             if (flush.full()) {
                 // disable refreshing, not dirty
                 dirty = false;
@@ -613,11 +627,7 @@ public class RobinEngine extends AbstractIndexShardComponent implements Engine,
             versionMap.clear();
             dirty = true; // force a refresh
             // we need to do a refresh here so we sync versioning support
-            refresh(new Refresh(true));
-            if (indexingSearcher.get() != null) {
-                indexingSearcher.get().release();
-                indexingSearcher.set(null);
-            }
+            refresh(new Refresh(true).force(true));
         } finally {
             rwl.writeLock().unlock();
             flushing.set(false);
@@ -628,6 +638,30 @@ public class RobinEngine extends AbstractIndexShardComponent implements Engine,
 //        }
     }
 
+    @Override public void maybeMerge() throws EngineException {
+        if (!possibleMergeNeeded) {
+            return;
+        }
+        possibleMergeNeeded = false;
+        rwl.readLock().lock();
+        try {
+            if (indexWriter == null) {
+                throw new EngineClosedException(shardId);
+            }
+            if (indexWriter.getMergePolicy() instanceof EnableMergePolicy) {
+                ((EnableMergePolicy) indexWriter.getMergePolicy()).enableMerge();
+            }
+            indexWriter.maybeMerge();
+        } catch (Exception e) {
+            throw new OptimizeFailedEngineException(shardId, e);
+        } finally {
+            rwl.readLock().unlock();
+            if (indexWriter != null && indexWriter.getMergePolicy() instanceof EnableMergePolicy) {
+                ((EnableMergePolicy) indexWriter.getMergePolicy()).disableMerge();
+            }
+        }
+    }
+
     @Override public void optimize(Optimize optimize) throws EngineException {
         if (optimizeMutex.compareAndSet(false, true)) {
             rwl.readLock().lock();
@@ -642,6 +676,7 @@ public class RobinEngine extends AbstractIndexShardComponent implements Engine,
                     indexWriter.expungeDeletes(false);
                 } else if (optimize.maxNumSegments() <= 0) {
                     indexWriter.maybeMerge();
+                    possibleMergeNeeded = false;
                 } else {
                     indexWriter.optimize(optimize.maxNumSegments(), false);
                 }
@@ -659,14 +694,11 @@ public class RobinEngine extends AbstractIndexShardComponent implements Engine,
         if (optimize.waitForMerge()) {
             indexWriter.waitForMerges();
         }
-        // once we did the optimization, we are "dirty" since we removed deletes potentially which
-        // affects TermEnum
-        dirty = true;
         if (optimize.flush()) {
             flush(new Flush());
         }
         if (optimize.refresh()) {
-            refresh(new Refresh(false));
+            refresh(new Refresh(false).force(true));
         }
     }
 
diff --git a/modules/elasticsearch/src/main/java/org/elasticsearch/index/shard/service/InternalIndexShard.java b/modules/elasticsearch/src/main/java/org/elasticsearch/index/shard/service/InternalIndexShard.java
index 7aeddcb538e..6f0d7398cb7 100644
--- a/modules/elasticsearch/src/main/java/org/elasticsearch/index/shard/service/InternalIndexShard.java
+++ b/modules/elasticsearch/src/main/java/org/elasticsearch/index/shard/service/InternalIndexShard.java
@@ -562,7 +562,7 @@ public class InternalIndexShard extends AbstractIndexShardComponent implements I
         // so, make sure we periodically call it, this need to be a small enough value so mergine will actually
         // happen and reduce the number of segments
         if (mergeInterval.millis() > 0) {
-            mergeScheduleFuture = threadPool.schedule(mergeInterval, ThreadPool.Names.MERGE, new EngineMerger());
+            mergeScheduleFuture = threadPool.schedule(mergeInterval, ThreadPool.Names.SAME, new EngineMerger());
             logger.debug("scheduling optimizer / merger every {}", mergeInterval);
         } else {
             logger.debug("scheduled optimizer / merger disabled");
@@ -616,27 +616,36 @@ public class InternalIndexShard extends AbstractIndexShardComponent implements I
 
     private class EngineMerger implements Runnable {
         @Override public void run() {
-            try {
-                // -1 means maybe merge
-                engine.optimize(new Engine.Optimize().maxNumSegments(-1).waitForMerge(false).flush(false).refresh(false));
-            } catch (EngineClosedException e) {
-                // we are being closed, ignore
-            } catch (OptimizeFailedEngineException e) {
-                if (e.getCause() instanceof InterruptedException) {
-                    // ignore, we are being shutdown
-                } else if (e.getCause() instanceof ClosedByInterruptException) {
-                    // ignore, we are being shutdown
-                } else if (e.getCause() instanceof ThreadInterruptedException) {
-                    // ignore, we are being shutdown
-                } else {
-                    logger.warn("Failed to perform scheduled engine optimize/merge", e);
+            if (!engine().possibleMergeNeeded()) {
+                if (state != IndexShardState.CLOSED) {
+                    mergeScheduleFuture = threadPool.schedule(mergeInterval, ThreadPool.Names.SAME, this);
                 }
-            } catch (Exception e) {
-                logger.warn("Failed to perform scheduled engine optimize/merge", e);
-            }
-            if (state != IndexShardState.CLOSED) {
-                mergeScheduleFuture = threadPool.schedule(mergeInterval, ThreadPool.Names.MERGE, this);
+                return;
             }
+            threadPool.executor(ThreadPool.Names.MERGE).execute(new Runnable() {
+                @Override public void run() {
+                    try {
+                        engine.maybeMerge();
+                    } catch (EngineClosedException e) {
+                        // we are being closed, ignore
+                    } catch (OptimizeFailedEngineException e) {
+                        if (e.getCause() instanceof InterruptedException) {
+                            // ignore, we are being shutdown
+                        } else if (e.getCause() instanceof ClosedByInterruptException) {
+                            // ignore, we are being shutdown
+                        } else if (e.getCause() instanceof ThreadInterruptedException) {
+                            // ignore, we are being shutdown
+                        } else {
+                            logger.warn("Failed to perform scheduled engine optimize/merge", e);
+                        }
+                    } catch (Exception e) {
+                        logger.warn("Failed to perform scheduled engine optimize/merge", e);
+                    }
+                    if (state != IndexShardState.CLOSED) {
+                        mergeScheduleFuture = threadPool.schedule(mergeInterval, ThreadPool.Names.SAME, EngineMerger.this);
+                    }
+                }
+            });
         }
     }