Frequently asked questions about DoubleCloud Managed ClickHouse®


Can I connect to a ClickHouse® cluster without SSL?

You can connect to DoubleCloud ClickHouse® clusters only via an SSL connection.

Will there be downtime during cluster update?

The ClickHouse® cluster update process depends on a number of its shards and hosts:

  • If your cluster has a single host, it will need to restart, and you'll have downtime during the restart process.

  • If your cluster has at least three hosts, they'll update and restart sequentially, so you'll experience no downtime.

What's the difference between shards and replicas?

  • Shards refer to the servers that contain different parts of the data (to read all the data, you must access all the shards).

  • Replicas are duplicating servers (to read all the data, you can access the data on any of the replicas).

What kind of cluster configuration provides high availability?

To provide high availability for your cluster, keep in mind the following:

  1. You must have at least 2 replicas per shard for ClickHouse® itself and 3 hosts for the ClickHouse Keeper

  2. In case of one of the ClickHouse® hosts going down, you should have at least one active replica to avoid the situation when the whole cluster goes down.

For production uses, we recommend going with dedicated ClickHouse Keeper hosts. The following table describes the minimal configurations when using dedicated and embedded ClickHouse Keeper hosts:

Dedicated Embedded
1 shard with 2 replicas 2 shards with 2 replicas each

The embedded ClickHouse Keeper solution requires at least 3 hosts running at any time, so you'll need to add one extra shard for enhanced fault-tolerance, and, since the shard configurations must be mirrored, you end up with a more expensive setup.

Can I create a read-only user for my ClickHouse® cluster?

To create a read-only user for your ClickHouse® cluster, see Manage ClickHouse® users.

I've run out of space on my cluster, and I'm already at the maximum storage capacity

If your cluster is at the maximum storage capacity, consider these options:

  • Select a higher resource preset.

    For example, the s2-c8-m32 preset has the maximum storage quota of 2 TB, while the s2-c32-m128 has the maximum quota of 8 TB.

  • If your cluster already has the maximum storage size of 8 TB, contact our technical support to request a storage quota increase.

What's the retention period for backups? Is there a limit to the number of backups?

DoubleCloud Managed ClickHouse® service stores the last 7 backups. These backups are created automatically every 24 hours, and the Managed ClickHouse® service retains each of them for 7 days.

When you create a manual backup by clicking Create backup, it adds another item to the list. The service will store this backup for 7 days.

How can I estimate the time needed to restore a cluster from a backup?

To estimate the time it takes to recover your cluster from a backup, use the average speed value of 100 megabits per second.

How can I see the disk space used by the tables?

To see the size of a table on your cluster, send the following query via the clickhouse-client:

SELECT database, name, formatReadableSize(total_bytes)
FROM system.tables
ORDER BY total_bytes DESC

Where can I see the prices for available ClickHouse® cluster configurations?

You can see the available configurations with estimated payment sizes at the Pricing page of our website.