add note on statement ordering in batch query

docs/topics/faq.rst

@@ -5,4 +5,46 @@ Frequently Asked Questions
 Q: Why don't updates work correctly on models instantiated as Model(field=blah, field2=blah2)?
 -------------------------------------------------------------------
 
-A: The recommended way to create new rows is with the models .create method. The values passed into a model's init method are interpreted by the model as the values as they were read from a row. This allows the model to "know" which rows have changed since the row was read out of cassandra, and create suitable update statements.
+A: The recommended way to create new rows is with the models .create method. The values passed into a model's init method are interpreted by the model as the values as they were read from a row. This allows the model to "know" which rows have changed since the row was read out of cassandra, and create suitable update statements.
+
+Q: How to preserve ordering in batch query?
+-------------------------------------------
+
+A: Statement Ordering is not supported by CQL3 batches. Therefore,
+once cassandra needs resolving conflict(Updating the same column in one batch),
+The algorithm below would be used.
+
+ * If timestamps are different, pick the column with the largest timestamp (the value being a regular column or a tombstone)
+ * If timestamps are the same, and one of the columns in a tombstone ('null') - pick the tombstone
+ * If timestamps are the same, and none of the columns are tombstones, pick the column with the largest value
+
+Below is an example to show this scenario.
+
+.. code-block:: python
+
+    class MyMode(Model):
+        id    = columns.Integer(primary_key=True)
+        count = columns.Integer()
+        text  = columns.Text()
+
+    with BatchQuery() as b:
+       MyModel.batch(b).create(id=1, count=2, text='123') 
+       MyModel.batch(b).create(id=1, count=3, text='111')
+
+    assert MyModel.objects(id=1).first().count == 3
+    assert MyModel.objects(id=1).first().text  == '123'
+
+The largest value of count is 3, and the largest value of text would be '123'.
+
+The workaround is applying timestamp to each statement, then Cassandra would
+resolve to the statement with the lastest timestamp.
+
+.. code-block:: python
+
+    with BatchQuery() as b:
+        MyModel.timestamp(datetime.now()).batch(b).create(id=1, count=2, text='123')
+        MyModel.timestamp(datetime.now()).batch(b).create(id=1, count=3, text='111')
+
+    assert MyModel.objects(id=1).first().count == 3
+    assert MyModel.objects(id=1).first().text  == '111'
+