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Mar 18, 2018
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Update read-concern.txt #3266

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12 changes: 6 additions & 6 deletions source/reference/read-concern.txt
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Expand Up @@ -136,16 +136,16 @@ The following read concern levels are available:

.. versionadded:: 3.6

MongoDB introduces the ``afterClusterTime`` option that can be set by
the drivers.
MongoDB 3.6 introduces the ``afterClusterTime`` option that can be set by
the drivers. To satisfy a read request with an ``afterClusterTime`` value of ``T`` a mongod must perform the request after its opLog reaches time ``T``. If its opLog has not reached time ``T`` the mongod must wait to service the request.

Read operations with a specified ``afterClusterTime``
return data that meet both the :ref:`read concern level <read-concern-levels>`
requirement and the specified ``afterClusterTime`` requirement.
requirement and the specified ``afterClusterTime`` requirement.

.. important::

Do not manually set the ``afterClusterTime``. MongoDB drivers set
Do not manually set ``afterClusterTime``. MongoDB drivers set
this value automatically for operations associated with
causally consistent sessions.

Expand All @@ -160,8 +160,8 @@ and :readconcern:`"majority"` read concern levels:
readConcern: { level: <"majority"|"local"> , afterClusterTime: <Timestamp> }

For read operations not associated with causally consistent sessions,
i.e. where the ``afterClusterTime`` is unset, reads against secondary members
have the default read concern level: :readconcern:`"available"`.
i.e. where ``afterClusterTime`` is unset, reads against secondary members
have the default read concern level: :readconcern:`"available"`, meaning that queries will return the instance’s most recent data. :readconcern:`"available"` provides no guarantee that data has been written to a majority of the replica set members. It might be rolled back.

.. _read-concern-storage-engine-drivers:

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