Manage cross-cluster replication in Aiven for Apache Cassandra® =============================================================== .. important:: Aiven for Apache Cassandra® cross-cluster replication (CCR) is a :doc:`limited availability feature `. If you're interested in trying out this feature, contact the sales team at `sales@Aiven.io `_. Learn how to update Apache Cassandra® services that has cross-cluster replication (CCR) enabled: change the service plan and add an extra disk space. Find out how to set up the replication factor and the consistency level for your CCR-enabled Apache Cassandra® services. Prerequisites ------------- Aiven-wise '''''''''' * Aiven account * Pair of Aiven for Apache Cassandra services with CCR enabled Tools ''''' * To update the service plan or add an extra disk space, use `Aiven Console `_. * To set up the replication factor on the database side, issue the CREATE KEYSPACE statement from `any supported client driver `_. This guide uses the ``cqlsh`` Cassandra client for that purpose to ensure general applicability of the instruction. * To set up the consistency level on the client side, configure it in your software. This guide uses the ``cqlsh`` Cassandra client for that purpose to ensure general applicability of the instruction. Change the service plan ----------------------- .. important:: When you change the plan for your CCR-enabled service, the plan for the connected replica service changes accordingly since the services constituting a CCR pair always share the same service plan. .. note:: It's recommended to use `Aiven Console `_ for changing the plan for a CCR-enabled service. 1. Log in to `Aiven Console `_. 2. From the **Services** page, select a CCR-enabled Aiven for Apache Cassandra service that you want to update. 3. On the **Overview** page of your service, select **Service settings** from the sidebar. 4. On the **Service settings** page of your service, navigate to the **Service plan** section, and select **Change plan** from the **Actions** (**...**) menu. 5. In the **Change service plan** window, select a new plan you want to use for your service. .. tip:: You can also add extra disk space for your service by using the slider in the **Additional disk storage** section. 6. Select **Change**. .. topic:: Result You've changed the plan for your CCR-enabled service and its CCR-replica service. Add an extra disk space ----------------------- .. important:: Changes to the storage space are applied to both services constituting the CCR pair so also affect the replica service. .. note:: It's recommended to use `Aiven Console `_ for adding storage space for CCR-enabled services. 1. Log in to `Aiven Console `_. 2. From the **Services** page, select a CCR-enabled Aiven for Apache Cassandra service that you want to update. 3. On the **Overview** page of your service, select **Service settings** from the sidebar. 4. On the **Service settings** page of your service, navigate to the **Service plan** section, and select **Add additional storage** from the **Actions** (**...**) menu. 5. In the **Upgrade service storage** window, use the slider to add extra disk space for your service. .. tip:: You can also change your service plan by selecting **Change plan** in the **Your current plan** section. 6. Select **Save changes**. .. topic:: Result You've added extra disk storage space for your CCR-enabled service and its CCR-replica service. .. _set-up-replication-factor: Set up the replication factor ----------------------------- You can specify how many replicas of your data you'd like to have on either of datacenters hosting your service. For that purpose, you need a keyspace with the ``NetworkTopologyStrategy`` replication. To create a keyspace that supports CCR and defines the replication factor, you need to run the ``CREATE KEYSPACE`` query with a set of parameters configuring the keyspace as needed. .. note:: This instruction uses the ``cqlsh`` Cassandra CLI client to configure the replication factor. ``cqlsh`` is used for demonstration purposes and the same statements can be executed using any `supported client driver `_. 1. :doc:`Connect to your service via cqlsh `. .. note:: You can connect to either of the two services constituting the CCR pair to set up the replication factor. 2. From the ``cqlsh`` shell, check out * Existing keyspaces with the ``DESCRIBE keyspaces;`` query (for a new service, only system keyspaces are returned) * Datacenters available for your service with the ``SELECT data_center from system.peers_v2;`` query. 3. Create a keyspace by running a query in which you specify * Replication strategy (``'class': 'NetworkTopologyStrategy'``) * Number of replicas to be created in the first datacenter (``'datacenter_1_name': 'number_of_replicas'``) * Number of replicas to be created in the second datacenter (``'datacenter_2_name': 'number_of_replicas'``) .. code-block:: bash CREATE KEYSPACE keyspace_name WITH replication = / { / 'class': 'NetworkTopologyStrategy', / 'datacenter_1_name': 'number_of_replicas', / 'datacaenter_2_name': 'number_of_replicas' / } / AND durable_writes = true; .. code-block:: bash :caption: Example CREATE KEYSPACE default WITH replication = / { / 'class': 'NetworkTopologyStrategy', / 'dc_1': '3', / 'dc_2': '3' / } / AND durable_writes = true; .. topic:: Result You've set up the replication factor for your keyspace. Now all data within this keyspace gets replicated to the datacenters according to the specified factor. .. seealso:: For more details on the replication factor for Apache Cassandra, see `NetworkTopologyStrategy `_ in the Apache Cassandra documentation. Set up the consistency level ---------------------------- For Apache Cassandra, you can set up the ``CONSISTENCY`` parameter, which regulates when the client can consider an operation as successfully completed. The ``CONSISTENCY`` parameter defines how many nodes need to confirm the operation as finalized before the client can acknowledge the operation as successfully completed. .. note:: You can configure the consistency level in the shell or in a client library. While using the ``cqlsh`` CLI client is convenient for setting up keyspaces or testing, configuring and using a `client driver `_ is recommended for operations in the production environment, such as data imports, data querying, or data reads/writes from/to databases. In the shell '''''''''''' .. note:: This instruction uses the ``cqlsh`` Cassandra CLI client to configure the consistency level. 1. :doc:`Connect to your service via cqlsh `. 2. Run ``CONSISTENCY;`` to check your current setting for the consistency level. Expected output: The query can return, for example, ``Current consistency level is ONE.``, which means that a confirmation of an operation completion on one node is enough for this operation to be considered as successful. 1. To set up the consistency level to a specific value, run the ``CONSISTENCY consistency_level_argument;`` query. Allowed consistency level arguments: For the list of the allowed consistency level arguments for Apache Cassandra, see `CONSISTENCY `_ in the Apache Cassandra documentation. .. code-block:: bash :caption: Example CONSISTENCY QUORUM; In a client library ''''''''''''''''''' To configure the consistency level in a client library, add an extra parameter or object to define the consistency level on your software component before running a particular query. .. topic:: Example: In Python, you can specify ``consistency_level`` as a parameter for the ``SimpleStatement`` object. .. code-block:: bash session.execute(SimpleStatement("LIST ROLES", consistency_level=ConsistencyLevel.ALL)) You've set up the consistency level for your service. Now operations on your data are considered as successfully completed according to the consistency level you specified. .. seealso:: For more details on consistency levels for Apache Cassandra, see `CONSISTENCY `_ in the Apache Cassandra documentation. More on Apache Cassandra CCR ---------------------------- * :doc:`About cross-cluster replication on Aiven for Apache Cassandra ` * :doc:`Enable CCR on Aiven for Apache Cassandra ` * :doc:`Disable CCR on Aiven for Apache Cassandra ` More on CCR with Aiven ---------------------- * :doc:`OpenSearch® cross-cluster replication` * :doc:`Set up cross-cluster replication for OpenSearch` * `Enabling cross-cluster replication for Apache Kafka® via Terraform `_.