Cassandra¶

This section is about how to perform a specific task. If you want to understand how a certain component works, please see Understanding wire-server components

The rest of the page assumes you installed using the ansible playbooks from wire-server-deploy

For any command below, first ssh into the server:

ssh <name or IP of the VM>

This section only covers the bare minimum, for more information, see the cassandra documentation

How to see cluster health¶

You want to see UN (Up & Normal) everywhere:

nodetool status

How to inspect tables and data manually¶

cqlsh
# from the cqlsh shell
describe keyspaces
use <keyspace>;
describe tables;
select * from <tablename> WHERE <primarykey>=<some-value> LIMIT 10;

How to rolling-restart a cassandra cluster¶

For maintenance you may need to restart the cluster.

On each server one by one:

check your cluster is healthy: nodetool status
nodetool drain && systemctl stop cassandra (to stop accepting writes and flush data to disk; then stop the process)
do any operation you need, if any
Start the cassandra daemon process: systemctl start cassandra
Wait for your cluster to be healthy again.
Do the same on the next server.