Connect Apache Kafka® to Aiven for ClickHouse® ============================================== You can integrate Aiven for ClickHouse® with either *Aiven for Apache Kafka®* service located in the same project, or *an external Apache Kafka endpoint*. A single Aiven for ClickHouse instance can connect to multiple Kafka clusters with different authentication mechanism and credentials. Behind the scenes the integration between Aiven for ClickHouse and Apache Kafka services relies on `ClickHouse Kafka Engine `_. .. note:: Aiven for ClickHouse service integrations are available for Startup plans and higher. Prerequisites ------------- You will need * Aiven for ClickHouse service * Aiven for Apache Kafka service or a self-hosted Apache Kafka service .. Tip:: If you use the self-hosted Apache Kafka service, an external Apache Kafka endpoint should be configured in **Integration endpoints**. * At least one topic in the Apache Kafka service Variables ------------- The following variables will be used later in the code snippets: ============================ ========================================================================================================== Variable Description ============================ ========================================================================================================== ``CLICKHOUSE_SERVICE_NAME`` Name of your Aiven for ClickHouse service. ``KAFKA_SERVICE_NAME`` Name of the Apache Kafka service you use for the integration. ``PROJECT`` Name of Aiven project where your services are located. ``CONNECTOR_TABLE_NAME`` Name of the Kafka engine virtual table that is used as a connector. ``DATA_FORMAT`` Input/output data format in which data is accepted into Aiven for ClickHouse. See :ref:`Reference `. ``CONSUMER_GROUP_NAME`` Name of the consumer group. Each message is delivered once per consumer group. ============================ ========================================================================================================== Create an integration ---------------------- To connect Aiven for ClickHouse and Aiven for Apache Kafka by enabling a data service integration, see :ref:`Create data service integrations `. The newly created database name has the following format: ``service_KAFKA_SERVICE_NAME``, where KAFKA_SERVICE_NAME is the name of your Apache Kafka service. .. note:: During this step we only created an empty database in Aiven for ClickHouse, but we didn't create any tables yet. Creation of the virtual connector table is done by setting specific integration configuration, see the section below. Update Apache Kafka integration settings ----------------------------------------- Next step is to configure the topic and data format options for the integration. This will create a virtual table in Aiven for ClickHouse that can receive and send messages from multiple topics. You can have as many of such tables as you need. For each table, there are mandatory and optional setting to be defined. Mandatory settings '''''''''''''''''' For each table, you need to define the following: * ``name`` - name of the connector table * ``columns`` - array of columns, with names and types * ``topics`` - array of topics, where you want to bring the data from * ``data_format`` - your preferred format for data input, see :doc:`/docs/products/clickhouse/reference/supported-input-output-formats` * ``group_name`` - consumer group name, that will be created on your behalf .. topic:: JSON format .. code-block:: json { "tables": [ { "name": "CONNECTOR_TABLE_NAME", "columns": [ {"name": "id", "type": "UInt64"}, {"name": "name", "type": "String"} ], "topics": [{"name": "topic1"}, {"name": "topic2"}], "data_format": "DATA_FORMAT", "group_name": "CONSUMER_NAME" } ] } Optional settings ''''''''''''''''' For each table, you can define the following optional settings: .. list-table:: :widths: 10 30 5 5 5 5 :header-rows: 1 * - Name - Description - Default value - Allowed values - Minimum value - Maximum value * - ``auto_offset_reset`` - Action to take when there is no initial offset in the offset store or the desired offset is out of range - ``earliest`` - ``smallest``, ``earliest``, ``beginning``, ``largest``, ``latest``, ``end`` - -- - -- * - ``date_time_input_format`` - Method to read ``DateTime`` from text input formats - ``basic`` - ``basic``, ``best_effort``, ``best_effort_us`` - -- - -- * - ``handle_error_mode`` - Method to handle errors for the Kafka engine - ``default`` - ``default``, ``stream`` - -- - -- * - ``max_block_size`` - Number of rows collected by poll(s) for flushing data from Kafka - ``0`` - ``0`` - ``1_000_000_000`` - ``0`` - ``1_000_000_000`` * - ``max_rows_per_message`` - Maximum number of rows produced in one Kafka message for row-based formats - ``1`` - ``1`` - ``1_000_000_000`` - ``1`` - ``1_000_000_000`` * - ``num_consumers`` - Number of consumers per table per replica - ``1`` - ``1`` - ``10`` - ``1`` - ``10`` * - ``poll_max_batch_size`` - Maximum amount of messages to be polled in a single Kafka poll - ``0`` - ``0`` - ``1_000_000_000`` - ``0`` - ``1_000_000_000`` * - ``skip_broken_messages`` - Minimum number of broken messages from Kafka topic per block to be skipped - ``0`` - ``0`` - ``1_000_000_000`` - ``0`` - ``1_000_000_000`` .. topic:: JSON format .. code-block:: json { "tables": [ { "name": "CONNECTOR_TABLE_NAME", "columns": [ {"name": "id", "type": "UInt64"}, {"name": "name", "type": "String"} ], "topics": [{"name": "topic1"}, {"name": "topic2"}], "data_format": "DATA_FORMAT", "group_name": "CONSUMER_NAME", "auto_offset_reset": "earliest" } ] } Configure integration with CLI -------------------------------- Currently the configurations can be set only with the help of CLI command :ref:`avn service integration-update ` Follow these instructions: 1. Get *the service integration id* by requesting the full list of integrations. Replace ``PROJECT``, ``CLICKHOUSE_SERVICE_NAME`` and ``KAFKA_SERVICE_NAME`` with the names of your services: .. code:: avn service integration-list \ --project PROJECT_NAME \ CLICKHOUSE_SERVICE_NAME | grep KAFKA_SERVICE_NAME 2. Update the configuration settings using the service integration id retrieved in the previous step and your integration settings. Replace ``SERVICE_INTEGRATION_ID``, ``CONNECTOR_TABLE_NAME``, ``DATA_FORMAT`` and ``CONSUMER_NAME`` with your values: .. code:: avn service integration-update SERVICE_INTEGRATION_ID \ --project PROJECT_NAME \ --user-config-json '{ "tables": [ { "name": "CONNECTOR_TABLE_NAME", "columns": [ {"name": "id", "type": "UInt64"}, {"name": "name", "type": "String"} ], "topics": [{"name": "topic1"}, {"name": "topic2"}], "data_format": "DATA_FORMAT", "group_name": "CONSUMER_NAME" } ] }' Read and store data ------------------- In Aiven for ClickHouse you can consume messages by running SELECT command. Replace ``KAFKA_SERVICE_NAME`` and ``CONNECTOR_TABLE_NAME`` with your values and run: .. code:: sql SELECT * FROM service_KAFKA_SERVICE_NAME.CONNECTOR_TABLE_NAME However, the messages are only read once (per consumer group). If you want to store the messages for later, you can send them into a separate ClickHouse table with the help of a materialized view. For example, run to creating a destination table: .. code:: sql CREATE TABLE destination (id UInt64, name String) ENGINE = ReplicatedMergeTree() ORDER BY id; Add a materialised view to bring the data from the connector: .. code:: sql CREATE MATERIALIZED VIEW materialised_view TO destination AS SELECT * FROM service_KAFKA_SERVICE_NAME.CONNECTOR_TABLE_NAME; Now the messages consumed from the Apache Kafka topic will be read automatically and sent into the destination table directly. .. seealso:: For more information on materialized views, see :doc:`Create materialized views in ClickHouse® `. .. note:: ClickHouse is strict about allowed symbols in database and table names. You can use backticks around the names when running ClickHouse requests, particularly in the cases when the name contains dashes. Write data back to the topic ---------------------------- You can also bring the entries from ClickHouse table into the Apache Kafka topic. Replace ``KAFKA_SERVICE_NAME`` and ``CONNECTOR_TABLE_NAME`` with your values: .. code:: sql INSERT INTO service_KAFKA_SERVICE_NAME.CONNECTOR_TABLE_NAME(id, name) VALUES (1, 'Michelangelo') .. warning:: Writing to more than one topic is not supported. .. _reference: Reference --------- When connecting ClickHouse® to Kafka® using Aiven integrations, data exchange requires using specific formats. Check the supported formats for input and output data in :doc:`Formats for ClickHouse®-Kafka® data exchange `.