src/cluster/databases.rst

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.. _cluster/databases:

===================
Database Management
===================

.. _cluster/databases/create:

Creating a database
===================

This will create a database with ``3`` replicas and ``8`` shards.

.. code-block:: bash

    curl -X PUT "http://xxx.xxx.xxx.xxx:5984/database-name?n=3&q=8" --user admin-user

The database is in ``data/shards``. Look around on all the nodes and you will
find all the parts.

If you do not specify ``n`` and ``q`` the default will be used. The default is
``3`` replicas and ``8`` shards.

.. _cluster/databases/delete:

Deleting a database
===================

.. code-block:: bash

    curl -X DELETE "http://xxx.xxx.xxx.xxx:5984/database-name --user admin-user

.. _cluster/databases/placement:

Placing a database on specific nodes
====================================

In BigCouch, the predecessor to CouchDB 2.0's clustering functionality, there
was the concept of zones. CouchDB 2.0 carries this forward with cluster
placement rules.

.. warning::

    Use of the ``placement`` argument will **override** the standard
    logic for shard replica cardinality (specified by ``[cluster] n``.)

First, each node must be labeled with a zone attribute. This defines which zone each node
is in. You do this by editing the node's document in the system ``_nodes`` database, which
is accessed node-local via the ``GET /_node/_local/_nodes/{node-name}`` endpoint.

Add a key value pair of the form:

.. code-block:: text

    "zone": "metro-dc-a"

Do this for all of the nodes in your cluster.

In your config file (``local.ini`` or ``default.ini``) on each node, define a
consistent cluster-wide setting like:

.. code-block:: text

    [cluster]
    placement = metro-dc-a:2,metro-dc-b:1

In this example, it will ensure that two replicas for a shard will be hosted
on nodes with the zone attribute set to ``metro-dc-a`` and one replica will
be hosted on a new with the zone attribute set to ``metro-dc-b``.

Note that you can also use this system to ensure certain nodes in the cluster
do not host *any* replicas for newly created databases, by giving them a zone
attribute that does not appear in the ``[cluster]`` placement string.