Cassandra writes - How many nodes?

Question

I'm probably just missing something here, but my search terms have all been to general to get meaningful results.

Assume RF = Replication Factor

When I write a value to the database, does it write the value to RF nodes or does it write it to one node and replicate it RF nodes?

Answer 1

That depends on the request you send. In the write request you can specify the consistency level:

• ALL: it will write to all RF nodes before returning
• QUORUM: it will write to a quorum of nodes before returning
• ONE: it writes to one node before returning. After returning it waits response from RF-1 nodes.
• LOCAL_QUORUM

...

See other possible values here: http://docs.datastax.com/en/cassandra/2.0/cassandra/dml/dml_config_consistency_c.html

Eventually all RF nodes will have the written data.