DOCS-4559: adds new glossary terms for 2.8

source/core/storage.txt

@@ -29,6 +29,8 @@ collections. Each database has a distinct set of data files and can
 contain a large number of collections. A single MongoDB deployment may
 have many databases.
 
+.. _storage-wiredtiger:
+
 WiredTiger Storage Engine
 -------------------------
 
@@ -61,7 +63,7 @@ the data files are *always* valid.
 The WiredTiger journal persists all data modifications between
 checkpoints. If MongoDB exits between checkpoints, it uses the journal
 to replay all data modified since the last checkpoint. By default the
-WiredTiger journal is compressed using the ``snappy`` algorithm.
+WiredTiger journal is compressed using the :term:`snappy` algorithm.
 
 You can disable journaling by setting :setting:`storage.journal.enabled`
 to ``false``, which can reduce the overhead of maintaining the
@@ -71,27 +73,31 @@ unexpectedly between
 checkpoints. For members of :term:`replica sets <replica set>`, the replication
 process may provide sufficient durability guarantees.
 
+.. _storage-wiredtiger-compression:
+
 Compression
 ~~~~~~~~~~~
 
 MongoDB supports compression for all collections and indexes using
-both block and prefix compression. Compression minimize storage use at the
-expense of additional computational requirements.
+both block and :term:`prefix compression`. Compression minimizes storage use at the
+expense of additional CPU.
 
-By default all indexes with the WiredTiger engine use prefix compression
-enabled. Also, by default all collections with WiredTiger use block
-compression with the ``snappy`` algorithm. Compression with ``zlib``
-compression is also available.
+By default, all indexes with the WiredTiger engine use :term:`prefix compression`.
+Also, by default all collections with WiredTiger use block
+compression with the :term:`snappy` algorithm. Compression with :term:`zlib`
+is also available.
 
 You can modify the default compression settings for all collections
 and indexes. Compression is also configurable on a per-collection and
 per-index basis during collection and index creation.
 
-For most workloads the default compression settings balance storage
+For most workloads, the default compression settings balance storage
 efficiency and processing requirements.
 
 .. TODO add link to wiredTiger configuration
 
+.. _storage-mmapv1:
+
 MMAPv1 Storage Engine
 ---------------------
 

source/includes/options-mongod.yaml

@@ -1614,31 +1614,31 @@ description: |
 
   - ``none``
 
-  - ``snappy``
+  - :term:`snappy`
 
-  - ``zlib``
+  - :term:`zlib`
 ---
 program: mongod
 name: wiredTigerCollectionBlockCompressor
 directive: option
 optional: true
-default: "snappy"
+default: "none"
 args: "<compressor>"
 description: |
 
   .. versionadded:: 2.8.0
 
-  Specifies the default type of compression to use to compress collection
-  data. You can override this on a per-collection basis when creating
-  collections.
+  Specifies the default type of compression to use to compress index
+  data. You can override this on a per-index basis when creating
+  indexes.
 
   Available compressors are:
 
   - ``none``
 
-  - ``snappy``
+  - :term:`snappy`
 
-  - ``zlib``
+  - :term:`zlib`
 ---
 program: mongod
 name: wiredTigerIndexPrefixCompression
@@ -1650,6 +1650,6 @@ description: |
 
   .. versionadded:: 2.8.0
 
-  Specify ``true`` for {{role}} to enable prefix compression for
+  Specify ``true`` for {{role}} to enable :term:`prefix compression` for
   index data.
 ...

source/reference/glossary.txt

@@ -615,6 +615,12 @@ Glossary
       :doc:`/reference/command/collMod` and
       :collflag:`usePowerOf2Sizes`.
 
+   prefix compression 
+      Reduces memory and disk consumption by storing any identical index
+      key prefixes only once, per page of memory. See:
+      :ref:`storage-wiredtiger-compression` for more about WiredTiger's
+      compression behavior.
+
    pre-splitting
       An operation performed before inserting data that divides the
       range of possible shard key values into chunks to facilitate easy
@@ -817,6 +823,16 @@ Glossary
       information on master/slave replication, see
       :doc:`/core/master-slave`.
 
+   snappy
+      A compression/decompression library designed to balance
+      efficient computation requirements with reasonable compression rates.
+      Snappy is the default compression
+      library for MongoDB's use of ':ref:`WiredTiger
+      <storage-wiredtiger>`. See: `Snappy
+      <https://code.google.com/p/snappy/>`_ and the `WiredTiger compression
+      documentation <http://source.wiredtiger.com/2.4.1/compression.html>`_
+      for more information.
+
    split
       The division between :term:`chunks <chunk>` in a :term:`sharded
       cluster`. See :doc:`/core/sharding-chunk-splitting`.
@@ -961,3 +977,12 @@ Glossary
       relevant chunk get applied to the proper shard. For related
       information, see :ref:`faq-writebacklisten` and
       :ref:`server-status-writebacksqueued`.
+
+   zlib
+      A data compression library that provides higher compression rates
+      at the cost of more CPU, compared to MongoDB's use of
+      :term:`snappy`. You can configure :ref:`WiredTiger
+      <storage-wiredtiger>` to use zlib as its compression library. See:
+      http://www.zlib.net and the `WiredTiger compression documentation
+      <http://source.wiredtiger.com/2.4.1/compression.html>`_ for more
+      information.

source/release-notes/2.8.txt

@@ -61,9 +61,9 @@ options. You can set :ref:`WiredTiger options on the command line
 All existing server, database, and collection reporting exposes
 statistics from WiredTiger.
 
-WiredTiger compresses collection data by default using ``snappy``.
+WiredTiger compresses collection data by default using :term:`snappy`.
 
-WiredTiger uses prefix compression on all indexes by default.
+WiredTiger uses :term:`prefix compression` on all indexes by default.
 
 Increased Number of Replica Set Members
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~