Integrating Apache Beam and ClickHouse

Apache Beam is an open-source, unified programming model that enables developers to define and execute both batch and stream (continuous) data processing pipelines. The flexibility of Apache Beam lies in its ability to support a wide range of data processing scenarios, from ETL (Extract, Transform, Load) operations to complex event processing and real-time analytics. This integration leverage ClickHouse’s official JDBC connector for the underlying insertion layer.

Integration package

The integration package required to integrate Apache Beam and ClickHouse is maintained and developed under Apache Beam I/O Connectors - an integrations bundle of many popular data storage systems and databases. org.apache.beam.sdk.io.clickhouse.ClickHouseIO implementation located within the Apache Beam repo.

Setup of the Apache Beam ClickHouse package

Package installation

Add the following dependency to your package management framework:

<dependency>
    <groupId>org.apache.beam</groupId>
    <artifactId>beam-sdks-java-io-clickhouse</artifactId>
    <version>${beam.version}</version>
</dependency>

The artifacts could be found in the official maven repository.

Code example

The following example reads a CSV file named input.csv as a PCollection, converts it to a Row object (using the defined schema) and inserts it into a local ClickHouse instance using ClickHouseIO:

package org.example;

import org.apache.beam.sdk.Pipeline;
import org.apache.beam.sdk.io.TextIO;
import org.apache.beam.sdk.io.clickhouse.ClickHouseIO;
import org.apache.beam.sdk.schemas.Schema;
import org.apache.beam.sdk.transforms.DoFn;
import org.apache.beam.sdk.transforms.ParDo;
import org.apache.beam.sdk.values.PCollection;
import org.apache.beam.sdk.values.Row;
import org.joda.time.DateTime;

public class Main {

    public static void main(String[] args) {
        // Create a Pipeline object.
        Pipeline p = Pipeline.create();

        Schema SCHEMA =
                Schema.builder()
                        .addField(Schema.Field.of("name", Schema.FieldType.STRING).withNullable(true))
                        .addField(Schema.Field.of("age", Schema.FieldType.INT16).withNullable(true))
                        .addField(Schema.Field.of("insertion_time", Schema.FieldType.DATETIME).withNullable(false))
                        .build();

        // Apply transforms to the pipeline.
        PCollection<String> lines = p.apply("ReadLines", TextIO.read().from("src/main/resources/input.csv"));

        PCollection<Row> rows = lines.apply("ConvertToRow", ParDo.of(new DoFn<String, Row>() {
            @ProcessElement
            public void processElement(@Element String line, OutputReceiver<Row> out) {

                String[] values = line.split(",");
                Row row = Row.withSchema(SCHEMA)
                        .addValues(values[0], Short.parseShort(values[1]), DateTime.now())
                        .build();
                out.output(row);
            }
        })).setRowSchema(SCHEMA);

        rows.apply("Write to ClickHouse",
                        ClickHouseIO.write("jdbc:clickhouse://localhost:8123/default?user=default&password=******", "test_table"));

        // Run the pipeline.
        p.run().waitUntilFinish();
    }
}

Supported data types

ClickHouseIO.Write parameters

You can adjust the ClickHouseIO.Write configuration with the following setter functions:

Limitations

Please consider the following limitations when using the connector:

• As of today, only Sink operation is supported. The connector doesn’t support Source operation.
• ClickHouse performs deduplication when inserting into a ReplicatedMergeTree or a Distributed table built on top of a ReplicatedMergeTree. Without replication, inserting into a regular MergeTree can result in duplicates if an insert fails and then successfully retries. However, each block is inserted atomically, and the block size can be configured using ClickHouseIO.Write.withMaxInsertBlockSize(long). Deduplication is achieved by using checksums of the inserted blocks. For more information about deduplication, please visit Deduplication and Deduplicate insertion config.
• The connector doesn’t perform any DDL statements; therefore, the target table must exist prior insertion.

Related content

• ClickHouseIO class documentation.
• Github repository of examples clickhouse-beam-connector.