Three simple rules for coding with the driver

When writing code that uses the driver, there are three simple rules that you should follow that make your code efficient:

  • Only use one Client instance per keyspace or use a single Client and explicitly specify the keyspace in your queries and reuse it in across your modules in the application lifetime.
  • If you execute a statement more than once, use a prepared statement.
  • In some situations you can reduce the number of network roundtrips and also have atomic operations by using batches.


The Client instance allows you to configure different important aspects of the way connections and queries are handled. At this level, you can configure everything from contact points (address of the nodes to be contacted initially before the driver performs node discovery), the request routing policy, retry and reconnection policies, and so on. Generally such settings are set once at the application level.

const cassandra = require('cassandra-driver');
const DCAwareRoundRobinPolicy = cassandra.policies.loadBalancing.DCAwareRoundRobinPolicy;
const client = new cassandra.Client({
   contactPoints: ['', '', ''], 
   localDataCenter: 'eu-west-3'

A Client instance is a long-lived object, and it should not be used in a request-response, short-lived fashion.

Your code should share the same Client instance across your application.

Prepared statements

Using prepared statements provides multiple benefits. A prepared statement is parsed and prepared on the Cassandra nodes and is ready for future execution. When binding parameters are provided, only they (and the query id) are sent over the wire. These performance gains add up when using the same queries (with different parameters) repeatedly. Additionally, when preparing, the driver retrieves information about the parameter types which allows an accurate mapping between a JavaScript type and a CQL type.

Preparing and executing statements in the driver does not require two chained asynchronous calls. You can set the prepare flag in the query options and the driver handles the rest.

const query = 'SELECT id, name FROM users WHERE id = ?';
client.execute(query, [ id ], { prepare: true }, callback);

Batch statements

The batch statement combines multiple data modification statements (INSERT, UPDATE, or DELETE) into a single logical operation that is sent to the server in a single request. Batching together multiple operations also ensures that they are executed in an atomic way, (that is, either all succeed or none). To make the best use of batch(), read about atomic batches in Cassandra 1.2, static columns and batching of conditional updates, and CQL documentation. But take into account that incorrect use of batch statements may increase load to servers.

Starting with Cassandra 2.0, prepared statements can be used in batch operations.

const queries = [
   { query: 'UPDATE user_profiles SET email=? WHERE key=?',
      params: [emailAddress, 'hendrix']},
   { query: 'INSERT INTO user_track (key, text, date) VALUES (?, ?, ?)',
      params: ['hendrix', 'Changed email', new Date()]}
const queryOptions = { prepare: true, consistency: cassandra.types.consistencies.quorum };
client.batch(queries, queryOptions, function(err) {
   console.log('Data updated on cluster');