Cassandra
--------------------------

.. include:: includes/intro.rst

This section only covers the bare minimum, for more information, see the `cassandra
documentation <https://cassandra.apache.org/doc/latest/>`__

How to see cluster health
~~~~~~~~~~~~~~~~~~~~~~~~~~

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

.. code:: sh

   nodetool status

How to inspect tables and data manually
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. code:: sh

   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:

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