Github user kxepal commented on a diff in the pull request:
https://github.com/apache/couchdb-documentation/pull/19#discussion_r28236027
--- Diff: src/cluster/sharding.rst ---
@@ -0,0 +1,289 @@
+.. Licensed under the Apache License, Version 2.0 (the "License"); you may
not
+.. use this file except in compliance with the License. You may obtain a
copy of
+.. the License at
+..
+.. http://www.apache.org/licenses/LICENSE-2.0
+..
+.. Unless required by applicable law or agreed to in writing, software
+.. distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT
+.. WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+.. License for the specific language governing permissions and limitations
under
+.. the License.
+
+.. _cluster/sharding:
+
+========
+Sharding
+========
+
+.. _cluster/sharding/scaling-out:
+
+Scaling out
+===========
+
+Normally you start small and grow over time. In the beginning you might do
just
+fine with one node, but as your data and number of clients grows, you need
to
+scale out.
+
+For simplicity we will start fresh and small.
+
+Start node1 and add a database to it. To keep it simple we will have 2
shards
+and no replicas.
+
+.. code-block:: bash
+
+ curl -X PUT "http://xxx.xxx.xxx.xxx:5984/small?n=1&q=2"; --user daboss
+
+If you look in the directory ``data/shards`` you will find the 2 shards.
+
+.. code-block:: text
+
+ data
+ shards
+ 00000000-7fffffff
+ small.1425202577.couch
+ 80000000-ffffffff
+ small.1425202577.couch
+
+Now, go to the admin panel
+
+.. code-block:: text
+
+ http://xxx.xxx.xxx.xxx:5986/_utils
+
+and look in the database ``_dbs``, it is here that the metadata for each
+database is stored. As the database is called small, there is a document
called
+small there. Let us look in it. Yes, you can get it with curl too:
+
+.. code-block:: javascript
+
+ curl -X GET "http://xxx.xxx.xxx.xxx:5986/_dbs/small";
+
+ {
+ "_id": "small",
+ "_rev": "1-5e2d10c29c70d3869fb7a1fd3a827a64",
+ "shard_suffix": [
+ 46,
+ 49,
+ 52,
+ 50,
+ 53,
+ 50,
+ 48,
+ 50,
+ 53,
+ 55,
+ 55
+ ],
+ "changelog": [
+ [
+ "add",
+ "00000000-7fffffff",
+ "[email protected]"
+ ],
+ [
+ "add",
+ "80000000-ffffffff",
+ "[email protected]"
+ ]
+ ],
+ "by_node": {
+ "[email protected]": [
+ "00000000-7fffffff",
+ "80000000-ffffffff"
+ ]
+ },
+ "by_range": {
+ "00000000-7fffffff": [
+ "[email protected]"
+ ],
+ "80000000-ffffffff": [
+ "[email protected]"
+ ]
+ }
+ }
+
+* ``_id`` The name of the database.
+* ``_rev`` The current revision of the metadata.
+* ``shard_suffix`` The numbers after small and before .couch. The number of
+ seconds after UNIX epoch that the database was created. Stored in ASCII.
+* ``changelog`` Self explaining.ãOnly for admins to read.
+* ``by_node`` Which shards each node have.
+* ``by_rage`` On which nodes each shard is.
+
+Nothing here, nothing there, a shard in my sleeve
+-------------------------------------------------
+
+Start node2 and add it to the cluster. Check in ``/_membership`` that the
+nodes are talking with each other.
+
+If you look in the directory ``data`` on node2, you will see that there is
no
+directory called shards.
+
+Go to Fauxton and edit the metadata for small, so it looks like this:
+
+.. code-block:: javascript
+
+ {
+ "_id": "small",
+ "_rev": "1-5e2d10c29c70d3869fb7a1fd3a827a64",
+ "shard_suffix": [
+ 46,
+ 49,
+ 52,
+ 50,
+ 53,
+ 50,
+ 48,
+ 50,
+ 53,
+ 55,
+ 55
+ ],
+ "changelog": [
+ [
+ "add",
+ "00000000-7fffffff",
+ "[email protected]"
+ ],
+ [
+ "add",
+ "80000000-ffffffff",
+ "[email protected]"
+ ],
+ [
+ "add",
+ "00000000-7fffffff",
+ "[email protected]"
+ ],
+ [
+ "add",
+ "80000000-ffffffff",
+ "[email protected]"
+ ]
+ ],
+ "by_node": {
+ "[email protected]": [
+ "00000000-7fffffff",
+ "80000000-ffffffff"
+ ],
+ "[email protected]": [
+ "00000000-7fffffff",
+ "80000000-ffffffff"
+ ]
+ },
+ "by_range": {
+ "00000000-7fffffff": [
+ "[email protected]",
+ "[email protected]"
+ ],
+ "80000000-ffffffff": [
+ "[email protected]",
+ "[email protected]"
+ ]
+ }
+ }
+
+Then press Save and marvel at the magic. The shards are now on node2 too!
We
+now have ``n=2``!
+
+If the shards are large, then you can copy them over manually and only have
+CouchDB syncing the changes from the last minutes instead.
+
+.. _cluster/sharding/move:
+
+Moving Shards
+=============
+
+When you get to ``n=3`` you should start moving the shards instead of
adding
+more replicas.
+
+.. warning::
+ If you have ``n<2`` then you have to stop all writes to the database
or you
+ will *LOSE DATA*!
--- End diff --
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