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# Apache Cassandra

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Apache Cassandra is a NoSQL multi-master database with linear scalability and no single point of failure.

## Installation

Install the cassandraAUR package.

## Configuration

### systemd unit

#### Logging to journald

The package logs to `/var/log/cassandra/system.log` by default. To instead log to journald you will need to edit the unit and set the service to run in the foreground by adding `-f` to the `ExecStart` line, and set Type to `simple` as the process will no longer fork.

This can be also done using a systemd drop-in file:

    /etc/systemd/system/cassandra.service.d/override.conf

    [Service]
    Type=simple
    ExecStart=
    ExecStart=/usr/bin/cassandra -p /run/cassandra/cassandra.pid -f

If Cassandra was running, you will need to drain, and then restart Cassandra.

    $ nodetool drain

### cassandra.yaml

There is copious amounts of documentation in the default `cassandra.yaml`. When installed via the cassandraAUR package, it is located in `/etc/cassandra/cassandra.yaml`

#### Basic configuration items to change

Setting the name of the cluster. This needs to be consistent for all nodes that you intend to have in this cluster.

    cluster_name: 'Test Cluster'

Set the directory where cassandra will write too, below is the default that will be used if unset. If possible set this to a disk used only for storing cassandra data

    data_file_directories:
        - /var/lib/cassandra/data

For the first node (the seed node) make sure to include its IP address in the seeds, and atleast 1 other node. for all other nodes, try and set a broad range of nodes in the cluster. If a node cannot connect to one of the seeds listed in this configuration at startup - it will fail to start.

    seed_provider:
        - class_name: org.apache.cassandra.locator.SimpleSeedProvider
          parameters:
              - seeds: "192.168.1.53, 192.168.1.52"

set this based on what type of disk cassandra is using to store data on `ssd` or `spinning`

    disk_optimization_strategy: ssd|spinning

This is the address Cassandra will listen for client connections on

    listen_address: 192.168.1.51

This is the address this node will advertise itself as, ensure both your clients and nodes can reach this node on this address

    broadcast_address: 192.168.1.51

This is the address used for thrift connections, set to `0.0.0.0` it will listen on all interfaces, which is fine as long as its firewalled for security

    rpc_address: 0.0.0.0

#### Troubleshooting

If Cassandra fails to run as a service, try running Cassandra

    $ cassandra

If you receive the following error:

    Improperly specified VM option 'ThreadPriorityPolicy=42'
    Error: Could not create the Java Virtual Machine.
    Error: A fatal exception has occurred. Program will exit.

Cassandra runs on Java 8 and starting with Cassandra 4.0.2, also on Java 11. You will need to install the proper Java and override the default JVM with a systemd drop-in file:

    /etc/systemd/system/cassandra.service.d/override.conf

    [Service]
    Environment=JAVA_HOME=/usr/lib/jvm/java-8-openjdk

If this file already exists, simply add the Environment line into the [Service] block.

Categories:

- Database management systems
- Apache