docs: function (db, query, callback) {
      // query parameter is optional
      if (!callback) {
        callback = query
        query = {}
      }
  
      // create a new request object
      var req = {
        // db name
        db: db,
        // authenticated url to db
        db_url: url.resolve(couch_url, encodeURIComponent(db)),
        // used by the update queue workers
        callback: callback,
        // store the query parameters
        query: query
      }
  
      // make sure the request has a since parameter set
      exports.updateSince(req, function (err, req) {
        if (err) {
          return callback(err)
        }
  
        // add the changes request to the pool
        exports.addToPool(idle, req)
      // queue the new request for immediate update
      // exports.refreshDB(updated, idle, db)
      })
    }