Data resharding in a Managed Service for ClickHouse® cluster

With Data Transfer, you can migrate your database from a Managed Service for ClickHouse® sharded source cluster to a Managed Service for ClickHouse® target cluster with a different shard configuration.

This method allows you to redistribute the sharded table data across the new ClickHouse® cluster shard configuration.

Migrate data with redistribution by shardsMigrate data with redistribution by shards

1. Prepare the source cluster.

2. Prepare the infrastructure:

   Manually

   Terraform

   1. Create a Managed Service for ClickHouse® target cluster with the computing capacity and storage size appropriate for the environment where the copied database is deployed.

      The database name in the target cluster must be the same as the source database name.

   2. Add the required number of shards to the Managed Service for ClickHouse® target cluster.

   3. Prepare the target cluster.

   4. Create a source endpoint:

      • Database type: ClickHouse

      • Endpoint parameters → Connection settings: Managed cluster

        Select a source cluster from the list and specify its connection settings.

   5. Create a target endpoint:

      • Database type: ClickHouse

      • Endpoint parameters → Connection settings: Managed cluster

        Select a target cluster from the list and specify its connection settings.

      • Endpoint parameters → Sharding settings → Sharding: Uniform random sharding

   6. Create a transfer of the Snapshot type that will use the created endpoints.

   7. Activate your transfer.

   1. If you do not have Terraform yet, install it.

   2. Get the authentication credentials. You can add them to environment variables or specify them later in the provider configuration file.

   3. Configure and initialize a provider. There is no need to create a provider configuration file manually, you can download it.

   4. Place the configuration file in a separate working directory and specify the parameter values. If you did not add the authentication credentials to environment variables, specify them in the configuration file.

   5. Download the data-transfer-mch-mch-resharding.tf configuration file to the same working directory.

      This file describes:

      • Network..
      • Subnet..
      • Security group and the rule required to connect to a cluster.
      • Managed Service for ClickHouse® target cluster with a given number of shards.
      • Source endpoint.
      • Target endpoint.
      • Transfer.

   6. In the data-transfer-mch-mch-resharding.tf file, specify:

      • Source endpoint parameters:

        • source_cluster: Managed Service for ClickHouse® source cluster ID.
        • source_user and source_pwd: Username and password to access the source.
        • source_db_name: Database name.

      • Target cluster parameters also used as target endpoint parameters:

        • target_clickhouse_version: ClickHouse® version.
        • target_user and target_password: Database owner username and password.

   7. Make sure the Terraform configuration files are correct using this command:

      terraform validate
      

      If there are any errors in the configuration files, Terraform will point them out.

   8. Create the required infrastructure:

      1. Run the command to view planned changes:

         terraform plan
         

         If the resource configuration descriptions are correct, the terminal will display a list of the resources to modify and their parameters. This is a test step. No resources are updated.

      2. If you are happy with the planned changes, apply them:

         1. Run the command:

            terraform apply
            

         2. Confirm the update of resources.

         3. Wait for the operation to complete.

      All the required resources will be created in the specified folder. You can check resource availability and their settings in the management console.

      Once created, your transfer will be activated automatically.

3. Wait for the transfer status to change to Completed.

   For more information about transfer statuses, see Transfer lifecycle.

Delete the resources you createdDelete the resources you created

Some resources are not free of charge. To avoid paying for them, delete the resources you no longer need:

ClickHouse® is a registered trademark of ClickHouse, Inc.