CappedCollection max_size normalized to multiple of 256

docs/changelog.rst

@@ -24,6 +24,7 @@ Changes in 0.9.X - DEV
 - Fixes some internal _id handling issue. #961
 - Updated URL and Email Field regex validators, added schemes argument to URLField validation. #652
 - Removed get_or_create() deprecated since 0.8.0. #300
+- Capped collection multiple of 256. #1011
 
 Changes in 0.9.0
 ================

docs/guide/defining-documents.rst

@@ -447,8 +447,10 @@ A :class:`~mongoengine.Document` may use a **Capped Collection** by specifying
 :attr:`max_documents` and :attr:`max_size` in the :attr:`meta` dictionary.
 :attr:`max_documents` is the maximum number of documents that is allowed to be
 stored in the collection, and :attr:`max_size` is the maximum size of the
-collection in bytes. If :attr:`max_size` is not specified and
-:attr:`max_documents` is, :attr:`max_size` defaults to 10000000 bytes (10MB).
+collection in bytes. :attr:`max_size` is rounded up to the next multiple of 256
+by MongoDB internally and mongoengine before. Use also a multiple of 256 to
+avoid confusions. If :attr:`max_size` is not specified and
+:attr:`max_documents` is, :attr:`max_size` defaults to 10485760 bytes (10MB).
 The following example shows a :class:`Log` document that will be limited to
 1000 entries and 2MB of disk space::