Index: src/main/java/org/apache/jackrabbit/core/SessionImpl.java
===================================================================
--- src/main/java/org/apache/jackrabbit/core/SessionImpl.java	(revision 1762532)
+++ src/main/java/org/apache/jackrabbit/core/SessionImpl.java	(working copy)
@@ -219,7 +219,7 @@
      * The stack trace knows who opened this session. It is logged
      * if the session is finalized, but Session.logout() was never called.
      */
-    private Exception openStackTrace = new Exception("Stack Trace");
+    private final Exception openStackTrace;
 
     /**
      * Protected constructor.
@@ -275,6 +275,8 @@
                 createObservationManager(wspConfig.getName()));
 
         versionMgr = createVersionManager();
+        // Avoid building the exception if warn level is not enabled as it is costly
+        this.openStackTrace = log.isWarnEnabled() ? new Exception("Stack Trace") : null;
     }
 
     /**
@@ -394,7 +396,7 @@
         // TODO: Q: shouldn't 'isSystem' rather be covered by instances of SystemSession only?
         return (subject != null && !subject.getPrincipals(SystemPrincipal.class).isEmpty());
     }
-    
+
     /**
      * Returns <code>true</code> if this session has been created for the
      * administrator. <code>False</code> otherwise.
@@ -1363,7 +1365,12 @@
     @Override
     public void finalize() {
         if (isLive()) {
-            log.warn("Unclosed session detected. The session was opened here: ", openStackTrace);
+            if (openStackTrace != null) {
+                // Log a warning if and only if openStackTrace is not null indicating that
+                // the warn level is enabled and the session has been fully created to prevent
+                // https://issues.apache.org/jira/browse/JCR-4033
+                log.warn("Unclosed session detected. The session was opened here: ", openStackTrace);
+            }
             logout();
         }
     }