merge: DOCS-458

Author: Sam Kleinman

draft/faq-sharding-addition.txt

@@ -1,54 +1,48 @@
-What are the best ways to successfully insert larger volumes of data into as sharded collection? 
-------------------------------------------------------------------------------------------------
+For high-volume inserts, when is it necessary to first pre-split data?
+----------------------------------------------------------------------
 
-- what is pre-splitting 
+Whether to pre-split before a high-volume insert depends on the
+:term:`shard key`, the existing distribution of :term:`chunks <chunk>`,
+and how evenly distributed the insert operation is.
 
-  In sharded environments, MongoDB distributes data into :term:`chunks
-  <chunk>`, each defined by a range of shard key values. Pre-splitting is a command run
-  prior to data insertion that specifies the shard key values on which to split up chunks.
+In the following cases, we recommend pre-splitting before a large insert:
 
-- Pre-splitting is useful before large inserts into a sharded collection when: 
+- Inserting data into an empty collection
 
-1. inserting data into an empty collection
+  If a collection is empty, the database takes time to determine the
+  optimal key distribution. If you insert many documents in rapid
+  succession, MongoDB initially directs writes to a single chunk, which
+  can affect performance. Predefining splits improves write performance
+  in the early stages of a bulk import by eliminating the database's
+  "learning" period.
 
-If a collection is empty, the database takes time to determine the optimal key
-distribution. If you insert many documents in rapid succession, MongoDB will initially
-direct writes to a single chunk, potentially having significant impacts on performance.
-Predefining splits may improve write performance in the early stages of a bulk import by
-eliminating the database's "learning" period.
+- Data is not evenly distributed
 
-2. data is not evenly distributed 
+  Even if the sharded collection contains existing documents balanced
+  over multiple chunks, :term:`pre-splitting` is beneficial if the write
+  operation itself isn't evenly distributed, i.e., if the inserts
+  include shard-key values that are contained on only a small number of
+  chunks. By pre-splitting and using an increasing shard key, you can
+  prevent writes from monopolizing a single :term:`shard`.
 
-Even if the sharded collection was previously populated with documents and contains multiple
-chunks, pre-splitting may be beneficial if the write operation isn't evenly distributed, in
-other words, if the inserts have shard keys values contained on a small number of chunks.
+- Monotomically increasing shard key.
 
-3. monotomically increasing shard key
+  If you attempt to insert data with monotonically increasing shard
+  keys, the writes will always occur on the last chunk in the
+  collection. Predefining splits helps to cycle a large write operation
+  around the cluster; however, pre-splitting in this instance will not
+  prevent consecutive inserts from hitting a single shard.
 
-If you attempt to insert data with monotonically increasing shard keys, the writes will
-always hit the last chunk in the collection. Predefining splits may help to cycle a large
-write operation around the cluster; however, pre-splitting in this instance will not
-prevent consecutive inserts from hitting a single shard.
+Pre-splitting might *not* be necessary in the following cases:
 
-- when does it not matter
+- If data insertion is not rapid, MongoDB may have enough time to split
+  and migrate chunks without affecting performance.
 
-If data insertion is not rapid, MongoDB may have enough time to split and migrate chunks without
-impacts on performance. In addition, if the collection already has chunks with an even key
-distribution, pre-splitting may not be necessary. 
+- If the collection already has chunks with an even key distribution,
+  pre-splitting may not be necessary.
 
-See the ":doc:`/tutorial/inserting-documents-into-a-sharded-collection`" tutorial for more
-information.
+For more information, see :doc:`/tutorial/inserting-documents-into-a-sharded-collection`.
 
-
-Is it necessary to pre-split data before high volume inserts into a sharded collection?
----------------------------------------------------------------------------------------
-
-The answer depends on the shard key, the existing distribution of chunks, and how
-evenly distributed the insert operation is. If a collection is empty prior to a
-bulk insert, the database will take time to determine the optimal key
-distribution. Predefining splits improves write performance in the early stages
-of a bulk import.
-
-Pre-splitting is also important if the write operation isn't evenly distributed.
-When using an increasing shard key, for example, pre-splitting data can prevent
-writes from hammering a single shard.
+.. SK, I flipped the above sentence, which could instead read:
+.. See :doc:`/tutorial/inserting-documents-into-a-sharded-collection` for more information.
+.. I prefer the former, but I think you prefer the latter. Let me know. -BG