Index: oak-core/src/main/java/org/apache/jackrabbit/oak/spi/commit/BackgroundObserver.java
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
--- oak-core/src/main/java/org/apache/jackrabbit/oak/spi/commit/BackgroundObserver.java	(revision 05b477f6673d9eb6bc7c2e0befb3a24fa6f52c0c)
+++ oak-core/src/main/java/org/apache/jackrabbit/oak/spi/commit/BackgroundObserver.java	(revision )
@@ -52,6 +52,8 @@
  */
 public class BackgroundObserver implements Observer, Closeable {
 
+    private static final Logger LOG = LoggerFactory.getLogger(BackgroundObserver.class);
+
     /**
      * Signal for the background thread to stop processing changes.
      */
@@ -104,6 +106,11 @@
     private volatile ListenableFutureTask currentTask = ListenableFutureTask.completed();
 
     /**
+     * The max queue length used for this observer's queue
+     */
+    private int maxQueueLength;
+
+    /**
      * Completion handler: set the current task to the next task and schedules that one
      * on the background thread.
      */
@@ -144,7 +151,8 @@
         this.observer = checkNotNull(observer);
         this.executor = checkNotNull(executor);
         this.exceptionHandler = checkNotNull(exceptionHandler);
-        this.queue = newArrayBlockingQueue(queueLength);
+        this.maxQueueLength = queueLength;
+        this.queue = newArrayBlockingQueue(maxQueueLength);
     }
 
     public BackgroundObserver(
@@ -172,6 +180,18 @@
     protected void added(int queueSize) { }
 
     /**
+     * Private utility to report queue size to observers
+     * @param queueSize current size of the queue
+     */
+    private void reportAdded(int queueSize){
+        if(queueSize == maxQueueLength ){
+            LOG.warn("Revision queue for observer {} is full (max = {}). Further revisions will be compacted.",
+                    observer != null ? observer.getClass().getName(): "", maxQueueLength);
+        }
+        added(queueSize);
+    }
+
+    /**
      * Clears the change queue and signals the background thread to stop
      * without making any further {@link #contentChanged(NodeState, CommitInfo)}
      * calls to the background observer. If the thread is currently in the
@@ -232,7 +252,7 @@
         // to onComplete are not a problem here since we always pass the same value.
         // Thus there is no question as to which of the handlers will effectively run.
         currentTask.onComplete(completionHandler);
-        added(queue.size());
+        reportAdded(queue.size());
     }
 
     //------------------------------------------------------------< internal >---