DOCS-13989 disallow lookup uncorrelated pipeline caching

Author: jason-price-mongodb

source/includes/uncorrelated-subquery.rst

@@ -0,0 +1,6 @@
+Starting in MongoDB 5.0, for an uncorrelated subquery in a
+:pipeline:`$lookup` pipeline stage containing a :pipeline:`$sample`
+stage, the :expression:`$sampleRate` operator, or the
+:expression:`$rand` operator, the subquery is always run again if
+repeated. Previously, depending on the subquery output size, either the
+subquery output was cached or the subquery was run again.

source/reference/operator/aggregation/lookup.txt

@@ -136,6 +136,10 @@ In MongoDB, a correlated subquery is a :ref:`pipeline
 document fields from a joined collection. An uncorrelated subquery does
 not reference joined fields.
 
+.. note::
+
+   .. include:: /includes/uncorrelated-subquery.rst
+
 MongoDB correlated subqueries are comparable to SQL correlated
 subqueries, where the inner query references outer query values. An
 SQL uncorrelated subquery does not reference outer query values.
@@ -780,11 +784,13 @@ the ``warehouses`` collection:
 Perform an Uncorrelated Subquery with ``$lookup``
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-.. versionchanged:: 3.6
+An aggregation pipeline :pipeline:`$lookup` stage can execute a pipeline
+on the joined collection, which allows uncorrelated subqueries. An
+uncorrelated subquery does not reference the joined document fields.
+
+.. note::
 
-   MongoDB 3.6 adds support for executing a pipeline on the joined
-   collection, which allows uncorrelated subqueries. An uncorrelated
-   subquery does not reference the joined document fields.
+   .. include:: /includes/uncorrelated-subquery.rst
 
 Create a collection ``absences`` with these documents:
 

source/release-notes/5.0.txt

@@ -200,6 +200,13 @@ stage supports :ref:`concise correlated subqueries
 <lookup-syntax-concise-correlated-subquery>` that improve joins between
 collections.
 
+``$lookup`` Stage: Uncorrelated Subqueries
+``````````````````````````````````````````
+
+.. include:: /includes/uncorrelated-subquery.rst
+
+See :ref:`lookup-uncorrelated-subquery`.
+
 .. _5.0-rel-notes-auditing:
 
 Auditing