Added new FAQs

FAQ

@@ -52,15 +52,43 @@ if it's able to find the task, or if some other error is happening.
 Why won't my Periodic Task run?
 -------------------------------
 
-See `Why won't my Task run?`_.
+**Answer:** See `Why won't my Task run?`_.
+
+How do I discard all waiting tasks?
+------------------------------------
+
+**Answer:** Use ``celery.task.discard_all()``, like this:
+
+    >>> from celery.task import discard_all
+    >>> discard_all()
+    1753
+
+The number ``1753`` is the number of messages deleted.
+
+You can also start celeryd with the ``--discard`` argument which will
+accomplish the same thing.
+
+I've discarded messages, but there are still messages left in the queue?
+------------------------------------------------------------------------
+
+**Answer:** Tasks are acknowledged (removed from the queue) as soon
+as they are actually executed. After the worker has received a task, it will
+take some time until it is actually executed, especially if there are a lot
+of tasks already waiting for execution. Messages that are not acknowledged are
+hold on to by the worker until it closes the connection to the broker (AMQP
+server). When that connection is closed (e.g because the worker was stopped)
+the tasks will be re-sent by the broker to the next available worker (or the
+same worker when it has been restarted), so to properly purge the queue of
+waiting tasks you have to stop all the workers, and then discard the tasks
+using ``discard_all``.
 
 Can I send some tasks to only some servers?
 --------------------------------------------
 
-As of now there is only one use-case that works like this, and that is
-tasks of type ``A`` can be sent to servers ``x`` and ``y``, while tasks
-of type ``B`` can be sent to server ``z``. One server can't handle more than
-one routing_key, but this is coming in a later release.
+**Answer:** As of now there is only one use-case that works like this,
+and that is tasks of type ``A`` can be sent to servers ``x`` and ``y``,
+while tasks of type ``B`` can be sent to server ``z``. One server can't
+handle more than one routing_key, but this is coming in a later release.
 
 Say you have two servers, ``x``, and ``y`` that handles regular tasks,
 and one server ``z``, that only handles feed related tasks, you can use this
@@ -123,3 +151,4 @@ You can also override this using the ``routing_key`` argument to
     >>> from myapp.tasks import RefreshFeedTask
     >>> apply_async(RefreshFeedTask, args=["http://cnn.com/rss"],
     ...             routing_key="feed.importer")
+