code: public void lockNode(final NodeId node) {
  		Lockable<SharedBufferNode> sharedBufferNode = sharedBuffer.getEntry(node);
  		if (sharedBufferNode != null) {
  			sharedBufferNode.lock();
  			sharedBuffer.upsertEntry(node, sharedBufferNode);
  		}
  	}
docs: Increases the reference counter for the given entry so that it is not
  accidentally removed.
  
  @param node id of the entry