[Docs][Data] Ordering of rows (ray-project#50986)

## Why are these changes needed?

Adds a section about impact of operators on ordering of rows to docs.

## Related issue number

Closes ray-project#50890 

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- Testing Strategy
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---------

Signed-off-by: jakac <matej.jakimov@gmail.com>
Signed-off-by: Richard Liaw <rliaw@berkeley.edu>
Co-authored-by: Richard Liaw <rliaw@berkeley.edu>

doc/source/data/transforming-data.rst

@@ -14,6 +14,7 @@ This guide shows you how to:
 
 * :ref:`Transform rows <transforming_rows>`
 * :ref:`Transform batches <transforming_batches>`
+* :ref:`Ordering of rows <ordering_of_rows>`
 * :ref:`Stateful transforms <stateful_transforms>`
 * :ref:`Groupby and transform groups <transforming_groupby>`
 
@@ -218,6 +219,26 @@ NumPy functions and model inference. However, if your batch size is too large, y
 program might run out of memory. If you encounter an out-of-memory error, decrease your
 ``batch_size``.
 
+.. _ordering_of_rows:
+
+Ordering of rows
+================
+
+When transforming data, the order of :ref:`blocks <data_key_concepts>` isn't preserved by default.
+
+If the order of blocks needs to be preserved/deterministic,
+you can use :meth:`~ray.data.Dataset.sort` method, or set :attr:`ray.data.ExecutionOptions.preserve_order` to `True`.
+Note that setting this flag may negatively impact performance on larger cluster setups where stragglers are more likely.
+
+.. testcode::
+
+   import ray
+
+   ctx = ray.data.DataContext().get_current()
+
+   # By default, this is set to False.
+   ctx.execution_options.preserve_order = True
+
 .. _stateful_transforms:
 
 Stateful Transforms