Index: oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/segment/SegmentNodeStore.java
===================================================================
--- oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/segment/SegmentNodeStore.java	(revision 1617082)
+++ oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/segment/SegmentNodeStore.java	(working copy)
@@ -51,6 +51,8 @@
 import org.apache.jackrabbit.oak.spi.state.NodeBuilder;
 import org.apache.jackrabbit.oak.spi.state.NodeState;
 import org.apache.jackrabbit.oak.spi.state.NodeStore;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 /**
  * The top level class for the segment store.
@@ -60,6 +62,8 @@
  */
 public class SegmentNodeStore implements NodeStore, Observable {
 
+    private static final Logger log = LoggerFactory.getLogger(SegmentNodeStore.class);
+
     static final String ROOT = "root";
 
     private final SegmentStore store;
@@ -235,6 +239,12 @@
                     if (store.setHead(state, newState)) {
                         refreshHead();
                         return name;
+                    } else {
+                        RecordId id = state.getRecordId();
+                        RecordId h = store.getHead().getRecordId();
+                        log.debug(
+                                "Unable to update the head state for checkpoint {}, local head state {}, store head state {} {}/5",
+                                new Object[] { name, id, h, i });
                     }
 
                 } finally {
@@ -243,6 +253,8 @@
             }
         }
 
+        log.debug("Failed to create checkpoint {}, available permits {}.", name,
+                commitSemaphore.availablePermits());
         return name;
     }