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Migrating from self-managed ClickHouse to ClickHouse Cloud using backup commands

Overview​

There are two primary methods to migrate data from self-managed ClickHouse (OSS) to ClickHouse Cloud:

  • Using the remoteSecure() function in which data is directly pulled/pushed.
  • Using BACKUP/RESTORE commands via cloud object storage

This migration guide focuses on the BACKUP/RESTORE approach and offers a practical example of migrating a database or full service in open source ClickHouse to Cloud via an S3 bucket.

Prerequisites

  • You have Docker installed
  • You have an S3 bucket and IAM user
  • You're able to create a new service ClickHouse Cloud service

To make the steps in this guide easy to follow along with and reproducible, we'll use one of the docker compose recipes for a ClickHouse cluster with two shards, and two replicas.

Cluster required

This backup method requires a ClickHouse cluster because tables must be converted from the MergeTree engine to ReplicatedMergeTree. If you're running a single instance, follow the steps in "Migrating between self-managed ClickHouse and ClickHouse Cloud using remoteSecure" instead.

OSS preparation​

We'll first spin up a ClickHouse cluster using a Docker Compose configuration from our examples repository. You can ignore spinning up the ClickHouse cluster if you already have one running.

  1. Clone the examples repository to your local machine
  2. From your terminal, cd into examples/docker-compose-recipes/recipes/cluster_2S_2R
  3. Make sure Docker is running, then start the ClickHouse cluster:
docker compose up

You should see:

[+] Running 7/7
 ✔ Container clickhouse-keeper-01  Created  0.1s
 ✔ Container clickhouse-keeper-02  Created  0.1s
 ✔ Container clickhouse-keeper-03  Created  0.1s
 ✔ Container clickhouse-01         Created  0.1s
 ✔ Container clickhouse-02         Created  0.1s
 ✔ Container clickhouse-04         Created  0.1s
 ✔ Container clickhouse-03         Created  0.1s

From a new terminal window at the root of the folder run the following command to connect to the first node of the cluster:

docker exec -it clickhouse-01 clickhouse-client

From MergeTree table to ReplicatedMergeTree table​

ClickHouse Cloud works with SharedMergeTree. When restoring a backup, ClickHouse automatically converts tables with ReplicatedMergeTree to SharedMergeTree tables.

It's likely your tables are already using the ReplicatedMergeTree engine if you're running a cluster. If not, you will need to convert any MergeTree tables to ReplicatedMergeTree before backing them up.

For the sake of demonstration of how to convert MergeTree tables to ReplicatedMergeTree, we will begin with a MergeTree table and convert it to ReplicatedMergeTree after wards. We're going to follow the first two steps of the New York taxi data guide to create a sample table and load data into it. Those steps are included below for your convenience.

Run the following commands to create a new database and insert data from an S3 bucket into a new table:

CREATE DATABASE nyc_taxi;

CREATE TABLE nyc_taxi.trips_small_adapted (
    trip_id             UInt32,
    pickup_datetime     DateTime,
    dropoff_datetime    DateTime,
    pickup_longitude    Nullable(Float64),
    pickup_latitude     Nullable(Float64),
    dropoff_longitude   Nullable(Float64),
    dropoff_latitude    Nullable(Float64),
    passenger_count     UInt8,
    trip_distance       Float32,
    fare_amount         Float32,
    extra               Float32,
    tip_amount          Float32,
    tolls_amount        Float32,
    total_amount        Float32,
    payment_type        Enum('CSH' = 1, 'CRE' = 2, 'NOC' = 3, 'DIS' = 4, 'UNK' = 5),
    pickup_ntaname      LowCardinality(String),
    dropoff_ntaname     LowCardinality(String)
)
ENGINE = MergeTree
PRIMARY KEY (pickup_datetime, dropoff_datetime);

INSERT INTO nyc_taxi.trips_small_adapted
SELECT
    trip_id,
    pickup_datetime,
    dropoff_datetime,
    pickup_longitude,
    pickup_latitude,
    dropoff_longitude,
    dropoff_latitude,
    passenger_count,
    trip_distance,
    fare_amount,
    extra,
    tip_amount,
    tolls_amount,
    total_amount,
    payment_type,
    pickup_ntaname,
    dropoff_ntaname
FROM s3(
    'https://datasets-documentation.s3.eu-west-3.amazonaws.com/nyc-taxi/trips_{0..2}.gz',
    'TabSeparatedWithNames'
);

Run the following command to DETACH the table.

DETACH TABLE nyc_taxi.trips_small_adapted;

Then attach it as replicated:

ATTACH TABLE nyc_taxi.trips_small_adapted AS REPLICATED;

Finally, restore the replica metadata:

SYSTEM RESTORE REPLICA nyc_taxi.trips_small_adapted;

Check that it was converted to ReplicatedMergeTree:

SELECT engine
FROM system.tables
WHERE name = 'trips_small_adapted' AND database = 'nyc_taxi';

┌─engine──────────────┐
│ ReplicatedMergeTree │
└─────────────────────┘

You're now ready to proceed with setting up your Cloud service in preparation for later restoring a backup from your S3 bucket.

Distributed tables with ReplicatedMergeTree​

If your setup uses distributed tables across multiple shards, you'll need a local ReplicatedMergeTree table on each node and a Distributed table as the query entry point.

Run the following command to create the local replicated table on all cluster nodes:

CREATE DATABASE IF NOT EXISTS nyc_taxi ON CLUSTER 'cluster_2S_2R';

CREATE TABLE nyc_taxi.trips_small_dist_local ON CLUSTER 'cluster_2S_2R'
(
    trip_id             UInt32,
    pickup_datetime     DateTime,
    dropoff_datetime    DateTime,
    pickup_longitude    Nullable(Float64),
    pickup_latitude     Nullable(Float64),
    dropoff_longitude   Nullable(Float64),
    dropoff_latitude    Nullable(Float64),
    passenger_count     UInt8,
    trip_distance       Float32,
    fare_amount         Float32,
    extra               Float32,
    tip_amount          Float32,
    tolls_amount        Float32,
    total_amount        Float32,
    payment_type        Enum('CSH' = 1, 'CRE' = 2, 'NOC' = 3, 'DIS' = 4, 'UNK' = 5),
    pickup_ntaname      LowCardinality(String),
    dropoff_ntaname     LowCardinality(String)
)
ENGINE = ReplicatedMergeTree('/clickhouse/tables/{database}/{table}/{shard}', '{replica}')
PRIMARY KEY (pickup_datetime, dropoff_datetime);

Then create the Distributed table on top:


CREATE TABLE nyc_taxi.trips_small_dist ON CLUSTER 'cluster_2S_2R'
(
    trip_id             UInt32,
    pickup_datetime     DateTime,
    dropoff_datetime    DateTime,
    pickup_longitude    Nullable(Float64),
    pickup_latitude     Nullable(Float64),
    dropoff_longitude   Nullable(Float64),
    dropoff_latitude    Nullable(Float64),
    passenger_count     UInt8,
    trip_distance       Float32,
    fare_amount         Float32,
    extra               Float32,
    tip_amount          Float32,
    tolls_amount        Float32,
    total_amount        Float32,
    payment_type        Enum('CSH' = 1, 'CRE' = 2, 'NOC' = 3, 'DIS' = 4, 'UNK' = 5),
    pickup_ntaname      LowCardinality(String),
    dropoff_ntaname     LowCardinality(String)
)
ENGINE = Distributed('cluster_2S_2R', 'nyc_taxi', 'trips_small_dist_local', rand());

Insert data through the distributed table:

INSERT INTO nyc_taxi.trips_small_dist
SELECT
    trip_id,
    pickup_datetime,
    dropoff_datetime,
    pickup_longitude,
    pickup_latitude,
    dropoff_longitude,
    dropoff_latitude,
    passenger_count,
    trip_distance,
    fare_amount,
    extra,
    tip_amount,
    tolls_amount,
    total_amount,
    payment_type,
    pickup_ntaname,
    dropoff_ntaname
FROM s3(
    'https://datasets-documentation.s3.eu-west-3.amazonaws.com/nyc-taxi/trips_{0..2}.gz',
    'TabSeparatedWithNames'
);

Cloud preparation​

You will be restoring your data into a new Cloud service. Follow the steps below to create a new Cloud service.

Open Cloud Console​

Go to https://console.clickhouse.cloud/

Create a new service​

Configure and create a service​

Choose your desired region and configuration, then click Create service

Create an access role​

Open SQL console

Set up S3 access​

To restore your backup from S3, you'll need to configure secure access between ClickHouse Cloud and your S3 bucket.

  1. Follow the steps in "Accessing S3 data securely" to create an access role and obtain the role ARN.

  2. Update the S3 bucket policy you created in "How to create an S3 bucket and IAM role" by adding the role ARN from the previous step.

Your updated policy for the S3 bucket will look something like this:

{
    "Version": "2012-10-17",
    "Id": "Policy123456",
    "Statement": [
        {
            "Sid": "abc123",
            "Effect": "Allow",
            "Principal": {
                "AWS": [
#highlight-start                  
                    "arn:aws:iam::123456789123:role/ClickHouseAccess-001",
                    "arn:aws:iam::123456789123:user/docs-s3-user"
#highlight-end                            
                ]
            },
            "Action": "s3:*",
            "Resource": [
                "arn:aws:s3:::ch-docs-s3-bucket",
                "arn:aws:s3:::ch-docs-s3-bucket/*"
            ]
        }
    ]
}

The policy includes both ARNs:

  • IAM user (docs-s3-user): Allows your self-managed ClickHouse cluster to back up to S3
  • ClickHouse Cloud role (ClickHouseAccess-001): Allows your Cloud service to restore from S3

Taking the backup (on self-managed deployment)​

Each shard must be backed up independently. Connect to a node on each shard and run the backup command with a unique destination path per shard.

Replace BUCKET_URL, KEY_ID and SECRET_KEY with your own AWS credentials. The guide "How to create an S3 bucket and IAM role" shows you how to obtain these if you don't yet have them.

Shard 1:

BACKUP DATABASE nyc_taxi
TO S3(
  'BUCKET_URL/backup_s1.zip',
  'KEY_ID',
  'SECRET_KEY'
)

Shard 2:

BACKUP DATABASE nyc_taxi
TO S3(
  'BUCKET_URL/backup_s2.zip',
  'KEY_ID',
  'SECRET_KEY'
)

If everything is correctly configured you will see a response similar to the one below containing a unique id assigned to the backup and the status of the backup.

Query id: efcaf053-75ed-4924-aeb1-525547ea8d45

┌─id───────────────────────────────────┬─status─────────┐
│ e73b99ab-f2a9-443a-80b4-533efe2d40b3 │ BACKUP_CREATED │
└──────────────────────────────────────┴────────────────┘
Single-node deployments

If you are not using distributed tables, you can back up the entire database with a single command:

BACKUP DATABASE nyc_taxi
TO S3(
  'BUCKET_URL',
  'KEY_ID',
  'SECRET_KEY'
)

If you check your previously empty S3 bucket you will now see some folders have appeared:

If you're performing a full migration then you can run the following command to backup the entire server:

BACKUP
TABLE system.users,
TABLE system.roles,
TABLE system.settings_profiles,
TABLE system.row_policies,
TABLE system.quotas,
TABLE system.functions,
ALL EXCEPT DATABASES INFORMATION_SCHEMA, information_schema, system
TO S3(
  'BUCKET_ID',
  'KEY_ID',
  'SECRET_ID'
)
SETTINGS
  compression_method='lzma',
  compression_level=3;

The command above backups up:

  • All user databases and tables
  • User accounts and passwords
  • Roles and permissions
  • Settings profiles
  • Row policies
  • Quotas
  • User-defined functions

If you're using a different Cloud Service Provider (CSP), you can use the TO S3() (for both AWS and GCP) and TO AzureBlobStorage() syntax.

For very large databases, consider using ASYNC to run the backup in the background:

BACKUP DATABASE my_database 
TO S3('https://your-bucket.s3.amazonaws.com/backup.zip', 'key', 'secret')
ASYNC;
       
-- Returns immediately with backup ID
-- Example result:
-- ┌─id──────────────────────────────────┬─status────────────┐
-- │ abc123-def456-789                   │ CREATING_BACKUP   │
-- └─────────────────────────────────────┴───────────────────┘

The backup id can then be used to monitor the progress of the backup:

SELECT * 
FROM system.backups 
WHERE id = 'abc123-def456-789'

It is also possible to take incremental backups. For more detail on backups in general, the reader is referred to the documentation for backup and restore.

Restore to ClickHouse Cloud​

Restore each shard's backup one at a time into your Cloud service. Set ROLE_ARN to the value obtained from "Accessing S3 data securely". Use SETTINGS allow_non_empty_tables=true on the second (and any subsequent) restore so that shard data is appended to the already-restored tables rather than failing on a conflict:

Shard 1:

RESTORE DATABASE nyc_taxi
FROM S3(
    'BUCKET_URL/backup_s1.zip',
    extra_credentials(role_arn = 'ROLE_ARN')
)

Shard 2:

RESTORE DATABASE nyc_taxi
FROM S3(
    'BUCKET_URL/backup_s2.zip',
    extra_credentials(role_arn = 'ROLE_ARN')
)
SETTINGS allow_non_empty_tables=true;
non-distributed deployments

If you are not using distributed tables, restore the database with a single command:

RESTORE DATABASE nyc_taxi
FROM S3(
    'BUCKET_URL',
    extra_credentials(role_arn = 'ROLE_ARN')
)

You can do a full service restore in a similar manner:

RESTORE
    TABLE system.users,
    TABLE system.roles,
    TABLE system.settings_profiles,
    TABLE system.row_policies,
    TABLE system.quotas,
    ALL EXCEPT DATABASES INFORMATION_SCHEMA, information_schema, system
FROM S3(
    'BUCKET_URL',
    extra_credentials(role_arn = 'ROLE_ARN')
)

After the restore completes, you can verify the data is available in Cloud:

-- ClickHouse Cloud restores everything in your local table
SELECT count() from nyc_taxi.trips_small_dist_local;
3000317

Since ClickHouse Cloud uses SharedMergeTree internally, the old distributed table is no longer needed. You can drop it and replace it with a view that preserves the original table name for your queries:

DROP TABLE drop table nyc_taxi.trips_small_dist;
CREATE VIEW nyc_taxi.trips_small_dist AS SELECT * FROM nyc_taxi.trips_small_dist_local;
SELECT count() from nyc_taxi.trips_small_dist;
3000317

Non-distributed ReplicatedMergeTree tables will be restored as SharedMergeTree:

SELECT count() FROM nyc_taxi.trips_small_adapted;
3000317