Defining Consistency Levels

Hector like Cassandra lets you use different consistency levels. These are:

• ANY: Wait until some replica has responded.
• ONE: Wait until one replica has responded.
• TWO: Wait until two replicas have responded.
• THREE: Wait until three replicas have responded.
• LOCAL_QUORUM: Wait for quorum on the datacenter the connection was stablished.
• EACH_QUORUM: Wait for quorum on each datacenter.
• QUORUM: Wait for a quorum of replicas (no matter which datacenter).
• ALL: Blocks for all the replicas before returning to the client.

In Hector, the Consistency Level can be set per Column Family and per operation type (Read, Write)

Note: The default value is Quorum for both read and write operations.

It is set by passing a ConfigurableConsistencyLevel object right when the Keyspace is created.

The following code assumes you have already created a Cluster like indicated at Initializing a cluster.

Let’s see a sample code:

// Create a customized Consistency Level
ConfigurableConsistencyLevel configurableConsistencyLevel = new ConfigurableConsistencyLevel();
Map<String, HConsistencyLevel> clmap = new HashMap<String, HConsistencyLevel>();

// Define CL.ONE for ColumnFamily "MyColumnFamily"
clmap.put("MyColumnFamily", HConsistencyLevel.ONE);

// In this we use CL.ONE for read and writes. But you can use different CLs if needed.
configurableConsistencyLevel.setReadCfConsistencyLevels(clmap);
configurableConsistencyLevel.setWriteCfConsistencyLevels(clmap);

// Then let the keyspace know
HFactory.createKeyspace("MyKeyspace", myCluster, configurableConsistencyLevel);

And that’s it.