code: public void releaseNode(final NodeId node) throws Exception {
  		Lockable<SharedBufferNode> sharedBufferNode = sharedBuffer.getEntry(node);
  		if (sharedBufferNode != null) {
  			if (sharedBufferNode.release()) {
  				removeNode(node, sharedBufferNode.getElement());
  			} else {
  				sharedBuffer.upsertEntry(node, sharedBufferNode);
  			}
  		}
  	}
docs: Decreases the reference counter for the given entry so that it can be
  removed once the reference counter reaches 0.
  
  @param node id of the entry
  @throws Exception Thrown if the system cannot access the state.