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.

Required paid resourcesRequired paid resources

The support cost includes:

• Managed Service for ClickHouse® cluster fee: Using computing resources allocated to hosts (including ZooKeeper hosts) and disk space (see Managed Service for ClickHouse® pricing).
• Fee for using public IP addresses if public access is enabled for cluster hosts (see Virtual Private Cloud pricing).
• Transfer fee: Using computing resources and the number of transferred data rows (see Data Transfer pricing).

Migrate data with redistribution by shardsMigrate data with redistribution by shards

1. Prepare the source cluster.

2. Set up your 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. Specify the following in the data-transfer-mch-mch-resharding.tf file:

      • Source endpoint parameters:

        • source_cluster: ID of the Managed Service for ClickHouse® source cluster.
        • 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: Name and user password of the database owner.

   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 this command to view the planned changes:

         terraform plan
         

         If you described the configuration correctly, the terminal will display a list of the resources to update and their parameters. This is a verification step that does not apply changes to your resources.

      2. If everything looks correct, apply the changes:

         1. Run this command:

            terraform apply
            

         2. Confirm updating the 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:

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