DOCSP 33887 Updating oplog sizing section (#218) (#229)

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* DOCSP-33887 editing faq

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Author: ltran-mdb2

source/faq.txt

@@ -49,13 +49,7 @@ clusters.
 Should I increase the size of the ``oplog`` in the source cluster?
 ------------------------------------------------------------------
 
-The :term:`oplog` is a capped collection that keeps a rolling 
-record of all operations that modify the data stored in your databases. 
-
-.. include:: /includes/fact-oplog-background
-
-To learn more about how to increase the size of the ``oplog``, see:
-:ref:`tutorial-change-oplog-size`. 
+.. include:: includes/fact-oplog-background.rst
 
 Which connection string options does ``mongosync`` allow?
 ---------------------------------------------------------

source/includes/fact-oplog-background.rst

@@ -4,14 +4,22 @@ to the data on the destination cluster.  When operations
 that ``mongosync`` has not applied roll off the ``oplog`` 
 on the source cluster, the sync fails and ``mongosync`` exits.
 
-During the initial sync, ``mongosync`` may apply operations at a slower
-rate due to the load imposed by copying documents concurrently.
-After ``mongosync`` completes the initial sync, it applies changes 
-faster and is more likely to maintain a position in the ``oplog``
-that is close to the real-time writes occuring on the source cluster.
+Starting in version 1.5.0, ``mongosync`` enables Oplog Rollover
+Resilience (ORR).  With ORR,  ``mongosync`` applies changes on the
+source cluster to the destination cluster during the initial sync. ORR
+increases the resilience of ``mongosync`` to oplog rollover but does not
+prevent rollover entirely.
+
+You might exceed the oplog window if you: 
+
+- Sync from a high write rate source cluster for an extended
+  period.
+- Pause sync for an extended period.
+
+To increase the size of the ``oplog`` on the source cluster, use
+:setting:`~replication.oplogSizeMB`. For more information, see
+:ref:`Change Oplog Size <tutorial-change-oplog-size>` and
+:ref:`Workloads that Might Requre a Large Oplog Size
+<replica-set-large-oplog-required>`.
 
-If you anticipate syncing a large data set, or if you plan to pause
-synchronization for an extended period of time, you might exceed the
-:term:`oplog window`. Use the :setting:`~replication.oplogSizeMB` setting
-to increase the size of the ``oplog`` on the source cluster.