DOCSP-45077 added pitr considerations (#530)

Author: kyuan-mongodb

source/tutorial/restore-pit-snapshot-http.txt

@@ -25,6 +25,39 @@ target snapshot host.
 
 .. include:: /images/restore-full-wt.rst
 
+Considerations
+--------------
+
+- The |mms| point-in-time restore might have oplog gaps in some
+  situations such as the following:
+
+  - If the oplog tailing stops because of an issue with :term:`backup
+    job <backup job>` tailing the oplog and the oplog rolls over before
+    {+mdbagent+} tails it again.
+
+  - After a topology change until |mms| completes a new snapshot.
+
+  - After the |fcv| change, which causes a gap between the time |mms| detects
+    the |fcv| change and |mms| completes a new snapshot. You can't apply a
+    point-in-time restore across MongoDB version changes.
+
+  - After a restore until |mms| completes a new snapshot.
+
+- If there is an oplog gap after |mms| takes the latest snapshot, then a
+  point-in-time restore fails if the restore time selected is after
+  the oplog gap began and before the next snapshot. Once |mms| takes the
+  next snapshot, you can use point-in-time restore as normal from that
+  snapshot time onward.
+
+- You only see oplog gaps when you attempt and fail a point-in-time
+  restore.
+
+- You can request a point-in-time restore to a specific point in time
+  that includes stale data.
+
+Procedure
+---------
+
 1. The user selects a timestamp:
 
    - Through the |mms| application: