4.3. Database Management

4.3.1. Creating a database

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

  1. 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.

4.3.2. Deleting a database

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

4.3.3. 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:

  1. "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:

  1. [cluster]
  2. 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.