DOCS-12534 Add Partial TTL Index Content (#5143) (#5246)

* DOCS-12534 Add Partial TTL Index Content

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Author: ianf-mongodb

source/core/index-partial.txt

@@ -160,6 +160,15 @@ by the filter expression
 
    db.contacts.find( { name: "xyz", email: { $exists: false } } )
 
+.. _partial-ttl-indexes:
+
+Partial TTL Indexes
+~~~~~~~~~~~~~~~~~~~
+
+Partial indexes can also be TTL indexes. Partial TTL indexes match the 
+specified filter expression and expire only those documents. For details, see
+:ref:`partial-ttl-index-example`. 
+
 Restrictions
 ------------
 

source/tutorial/expire-data.txt

@@ -163,6 +163,54 @@ specified in ``expireAfterSeconds``.
    object is older than the number of seconds specified in
    ``expireAfterSeconds``.
 
+.. _partial-ttl-index-example:
+
+Expire Documents with Filter Conditions
+---------------------------------------
+
+To expire documents with specific filter expressions, you can create
+an index that is both a :ref:`partial <index-type-partial>` 
+and a :ref:`TTL <index-feature-ttl>` index.
+
+Create a partial TTL index:
+
+.. code-block:: javascript
+   :emphasize-lines: 5-6
+
+   db.foo.createIndex( 
+      { F: 1 }, 
+      { 
+         name: "Partial-TTL-Index", 
+         partialFilterExpression: { D : 1 }, 
+         expireAfterSeconds: 10 
+      }
+   )
+
+Insert two documents, one of which matches the filter expression 
+``{ D : 1 }`` of the ``partialFilterExpression``:
+
+.. code-block:: javascript
+   :emphasize-lines: 3
+
+   db.foo.insertMany( [
+      { "F" : ISODate("2019-03-07T20:59:18.428Z"), "D" : 3},
+      { "F" : ISODate("2019-03-07T20:59:18.428Z"), "D" : 1}
+   ] )
+
+Wait for ten seconds then query the ``foo`` collection:
+
+.. code-block:: javascript
+
+   db.foo.find({}, {_id: 0, F: 1, D: 1})
+
+The document that matches the ``partialFilterExpression`` 
+of ``{ D : 1 }`` is deleted (expired). As a result, only 
+one document remains in the ``foo`` collection:
+
+.. code-block:: javascript
+
+   { "F" : ISODate("2019-03-07T20:59:18.428Z"), "D" : 3}
+
 Expire Documents at a Specific Clock Time
 -----------------------------------------