Routing queries

When using the default load-balancing policy (DefaultLoadBalancingPolicy) or TokenAwarePolicy, the driver uses the RoutingKey to determine which node is used as coordinator for a given statement.

Note that the internal TokenMap must be up to date in order for this feature to work correctly. If metadata synchronization is enabled (which it is by default), then the driver will automatically keep it up to date. For more information on metadata synchronization, check out this page.

Prepared statements

When using prepared statements, the driver will determine which of the query parameters compose the partition key based on the prepared statement metadata.

Consider a table users that has a single partition key, id.

PreparedStatement prepared = session.Prepare(
      "INSERT INTO users (id, name) VALUES (?, ?)");

When binding the parameters, the driver knows which parameter corresponds to the partition key.

BoundStatement bound = prepared.Bind(Guid.NewGuid(), "Franz Ferdinand");
session.Execute(bound);

As a rule of thumb, use prepared statements and the driver does all the routing for you.

Simple statements

If you need to use a simple statement with routing, you must specify the routing values.

var id = Guid.NewGuid();
var query = new SimpleStatement(
      "INSERT INTO users (id, name) VALUES (?, ?)", id, "Franz Ferdinand");
// You must specify the values that compose the partition key
query.SetRoutingValues(id);
session.Execute(query);

Batch statements

If you want to enable routing for batch statements, you must specify the routing values.

var partitionKey = Guid.NewGuid();
var batch = new BatchStatement();
// ... Add statements to the query
// You must specify the values that compose the partition key
batch.SetRoutingValues(partitionKey);
session.Execute(batch);