DOCS-362 capped collections _id behavior change for 2.2

Author: Sam Kleinman

source/core/indexes.txt

@@ -68,7 +68,7 @@ _id
 
 The ``_id`` index is a :ref:`unique index <index-type-unique>`
 [#unique-index-report]_ on the ``_id`` field, and MongoDB creates this
-index by default on all collections, except for capped collections. [#capped-collections]_
+index by default on all collections. [#capped-collections]_
 You cannot delete the index on ``_id``.
 
 The ``_id`` field is the :term:`primary key` for the collection, and
@@ -90,12 +90,11 @@ is a 12-byte unique identifiers suitable for use as the value of an
    the :func:`getIndexes() <db.collection.getIndexes()>` method will
    *not* print ``unique: true`` in the :program:`mongo` shell.
 
-.. [#capped-collections] Capped collections are special collections
-   that do not have an ``_id`` index by default. If you specify
-   ``autoIndexId: true`` when creating a capped collection MongoDB will
-   create an ``_id`` index on this collection. Replica set members may
-   create ``_id`` indexes on capped collections during the replication
-   process.
+.. [#capped-collections] Before version 2.2 capped collections did not
+   have an ``_id`` field by default. In 2.2, all capped collections
+   have an ``_id`` field, except those in the ``local``
+   :term:`database`. See the :ref:`release notes
+   <2.2-id-indexes-capped-collections>` for more information.
 
 .. TODO fix the above when a full capped-collection page exists.
 

source/release-notes/2.2.txt

@@ -382,6 +382,8 @@ Additional Improvements
 use and state. In previous versions, these data were sampled. See
 :issue:`SERVER-5784` and :status:`indexCounters` for more information.
 
+.. _2.2-id-indexes-capped-collections:
+
 ``_id`` Indexes on Capped Collections
 `````````````````````````````````````