code: function compactDb (dbName, ddoc, callback) {
      if (typeof ddoc === 'function') {
        callback = ddoc
        ddoc = null
      }
      return relax({
        db: dbName,
        doc: '_compact',
        att: ddoc,
        method: 'POST'
      }, callback)
    }
docs: http://docs.couchdb.org/en/latest/api/database/compact.html#post--db-_compact