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FAQ about Managed Service for ClickHouse®

Written by
Updated at December 10, 2025

General questions

Questions about ClickHouse®

Connection

Updating a cluster

Cluster parameter settings

Moving and restoring a cluster

Monitoring and logs

General questions

What is Managed Service for ClickHouse®?

Managed Service for ClickHouse® is a solution that helps you create, operate, and scale ClickHouse® databases in the cloud.

With Managed Service for ClickHouse®, you can:

  • Create a database with performance tailored to your needs.
  • Scale your database compute and dedicated storage capacity as needed.
  • Get database logs.

Managed Service for ClickHouse® takes over time-consuming administrative tasks in ClickHouse®:

  • Monitors your resource consumption.
  • Automatically backs up your databases.
  • Ensures fault tolerance through automatic failover to standby replicas.
  • Keeps your DBMS software up to date.

You work with a Managed Service for ClickHouse® database cluster just like with your regular local database. Thus, you can manage internal database settings to meet your application requirements.

What is ClickHouse® used for? Which DBMS should I select?

ClickHouse® is designed primarily for analytics (OLAP) and only supports adding and reading data. You can update data but with certain limitations. For other purposes, you might want to use another DBMS.

What is the role of Managed Service for ClickHouse® in database management and maintenance?

When you create clusters, Managed Service for ClickHouse® allocates resources, installs the DBMS, and creates databases.

For all created and running databases, Managed Service for ClickHouse® automatically creates backups as well as applies DBMS patches and updates.

Furthermore, Managed Service for ClickHouse® ensures data replication across database hosts, both within and across availability zones, with automatic failover to a standby replica if a failure occurs.

Be mindful of what is what is controlled by the service, and what by the Yandex Cloud customer. Understanding these control zones will help you use your cloud resources effectively and avoid potential database-related problems. For more information, see Zones of control between managed database (MDB) service users and Yandex Cloud.

Not sure whether to use Managed Service for ClickHouse® or VMs running databases?

Yandex Cloud offers two ways to work with databases:

  • With Managed Service for ClickHouse®, you can use template databases, with no administrative effort required.
  • With Yandex Compute Cloud virtual machines, you can create and customize your own databases. This approach allows you to use any database management system, connect to databases over SSH, and many more.

What is a database host and database cluster?

A database host is a cloud-based isolated database environment with dedicated computing resources and reserved storage capacity.

A database cluster consists of one or more database hosts with configurable replication across them.

How do I get started with Managed Service for ClickHouse®?

Managed Service for ClickHouse® is available to all registered Yandex Cloud users.

Before creating a database cluster in Managed Service for ClickHouse®, you need to decide on its configuration:

  • Host class that will determine your computing power, i.e., vCPUs, RAM, and more.
  • Storage size (fully reserved when creating the cluster).
  • Network for your cluster.
  • Number of hosts in your cluster and availability zone for each host.

For more information, see Getting started.

How many database hosts can be in a cluster?

The minimum number of hosts in a cluster depends on the following:

  • Storage type:

    • At least three hosts for non-replicated SSDs (network-ssd-nonreplicated).

    • At least two hosts for local SSDs (local-ssd).

    • At least one host for the following disk types:

      • Network HDDs (network-hdd)
      • Network SSDs (network-ssd)
      • Ultra high-speed network SSDs with three replicas (network-ssd-io-m3)

  • Cluster sharding. When sharding is enabled, you need to multiply the minimum number of hosts for the selected disk type by the number of shards.

    For more information on the features and limitations of sharding in ClickHouse®, see this article.

The maximum number of hosts per cluster cannot exceed the set limits.

For more information, see Quotas and limits.

How can I access a running database host?

You can connect to Managed Service for ClickHouse® databases using conventional DBMS methods.

Learn more about connecting to clusters in this guide.

How many clusters can I create within a single cloud?

To learn more about MDB technical and organizational limitations, see Quotas and limits.

How are database clusters maintained?

Maintenance in Managed Service for ClickHouse® includes:

  • Automatic installation of DBMS updates and patches for all hosts, even disabled ones.
  • Changes in the host class and storage size.
  • Other Managed Service for ClickHouse® maintenance activities.

For more information, see Maintenance.

How do I edit external dictionaries?

To rename a dictionary, run this query:

RENAME DICTIONARY <dictionary_name> TO <new_name>

For other changes, use the update API method.

Which ClickHouse® version does Managed Service for ClickHouse® use?

Managed Service for ClickHouse® uses multiple latest stable versions of ClickHouse®. For more information, see ClickHouse® versioning policy.

Which ClickHouse® version should I choose?

We recommend the latest available LTS version of ClickHouse®. For more information, see ClickHouse® versioning policy.

What happens when a new DBMS version is released?

When new minor versions are released, the cluster software is automatically updated after a short testing period.

Owners of affected database clusters are notified of an expected maintenance period and database availability in advance.

What happens when a DBMS version becomes deprecated?

When a DBMS version becomes deprecated, Managed Service for ClickHouse® automatically sends email notifications to the owners of database clusters created with this version.

New hosts can no longer be created using deprecated DBMS versions. Clusters running a deprecated ClickHouse® version are updated according to the versioning policy.

Owners of affected database clusters are notified of an expected maintenance period and database availability in advance.

How do you calculate usage cost for a database host?

In Managed Service for ClickHouse®, the usage cost is calculated based on the following:

  • Selected host class.
  • Reserved storage capacity for the database host.
  • Size of database cluster backups. You are not charged for storing backups up to your storage size. Additional backup storage is charged according to our pricing policy.
  • Database host uptime in hours. Partial hours are rounded to the nearest whole hour. For the cost per hour of operation for each host class, see our pricing policy.

How much does it cost to use my cluster?

In the management console, navigate to the folder dashboard, select Managed Service for ClickHouse, and click the cluster you need. On the right side of the screen, you will see the cluster usage cost per month. For more information, see our pricing policy.

How can I change the computing resources and storage size for a database cluster?

You can scale your computing resources and storage size directly in the management console by selecting a different host class for your cluster.

The cluster settings will update within 30 minutes. This window may also be used for other maintenance activities, such as installing updates.

How can I fix the no permission error when attaching a service account to a cluster?

Error message:

ERROR: rpc error: code = PermissionDenied desc = you do not have permission to access the requested service account or service account does not exist

The error occurs in the following cases:

  • You are creating or modifying a cluster and linking it to a service account.
  • You are restoring a cluster linked to a service account from its backup.

To fix this error, assign your Yandex Cloud account the iam.serviceAccounts.user role or higher.

Does the service meet the requirements of the Russian Federation Federal Law 152-FZ on personal data?

Yes, it does. You can read the full security audit conclusion here.

Can I get logs of my operations in Yandex Cloud?

Yes, you can request information about operations with your resources from Yandex Cloud logs. Do it by contacting support.

Questions about ClickHouse®

Why should I use ClickHouse® in Managed Service for ClickHouse® rather than my own VM-based installation?

Managed Service for ClickHouse® automates routine database maintenance:

  • Quick DB deployment with the required available resources.

  • Data backup.

  • Regular software updates.

  • Ensuring DB cluster fault tolerance.

  • Database usage monitoring and statistics.

When should I use ClickHouse® rather than PostgreSQL?

ClickHouse® only supports adding and reading data since it is primarily designed for analytics (OLAP). For other purposes, you might want to use PostgreSQL.

How do I load data into ClickHouse®?

Use the INSERT statement described in this ClickHouse® article.

How do I load a large data volume into ClickHouse®?

Use the CLI to efficiently compress data when transferring it (we recommend issuing no more than one INSERT command per second).

Currently, data transfer from physical media is not supported.

What will happen to my cluster if one of its nodes fails?

DB clusters consist of at least two replicas, so if one node is down, the cluster will keep running.

You may lose data only if a node with a non-replicated table fails.

Can I deploy a ClickHouse® database cluster in multiple availability zones?

Yes. A database cluster may consist of hosts residing in different availability zones or even regions.

How does replication work for ClickHouse®?

Managed Service for ClickHouse® clusters use ClickHouse® Keeper or ZooKeeper for replication. In the first case, replication and fault tolerance are enabled by default, so no further configuration is needed. In the second case, each ClickHouse® cluster comes with a ZooKeeper cluster containing at least three hosts.

Yandex Cloud users do not have access to ZooKeeper and cannot configure it.

Why does my ClickHouse® cluster use three extra hosts?

When creating a ClickHouse® cluster of two or more hosts, Managed Service for ClickHouse® automatically creates a cluster of three ZooKeeper hosts to manage replication and fault tolerance, unless ClickHouse® Keeper support is enabled. These hosts are counted towards both the cloud resource quota and the cluster cost. By default, ZooKeeper hosts come with the minimum host class.

For more information about using ZooKeeper, see this ClickHouse® article.

How does ClickHouse® handles data deletion based on TTL?

With TTL, data is deleted in parts or during merges rather than in rows.

Deleting entire data parts is more efficient and uses less server resources, but requires the TTL expression and partitioning key to match or be of the same granularity for all rows in a data part.

Deleting data during merges uses more resources and takes place either along with regular background merges or during unscheduled merges. Merge frequency is defined by the merge_with_ttl_timeout parameter, which indicates the minimum time in seconds before a repeat merge to process data with expired TTL. You set this parameter when creating the table. The default value is 14,400 seconds (4 hours).

We recommend managing data with TTL so that old data is always deleted in data parts. To do this, set ttl_only_drop_parts to true when creating tables.

Can I use JSON data for tables in ClickHouse®?

Yes, you can. However, JSON is currently an experimental data type in ClickHouse®. To allow creating tables of this type, run this query:

SET allow_experimental_object_type=1;

Note

The SET queries are not supported when connecting to a cluster via the management console. To run such a query, use a different cluster connection method, e.g., via clickhouse-client.

Make sure you have the latest client version installed.

For more information, see this ClickHouse® article.

Why is my cluster slow even though the computing resources are not fully utilized?

Your storage may have insufficient maximum IOPS and bandwidth to process the current number of requests. In this case, throttling occurs, which degrades the entire cluster performance.

The maximum IOPS and bandwidth values increase by a fixed value when the storage size increases by a certain step. The step and increment values depend on the disk type:

Disk type Step, GB Max IOPS increase (read/write) Max bandwidth increase (read/write), MB/s
network-hdd 256 300/300 30/30
network-ssd 32 1,000/1,000 15/15
network-ssd-nonreplicated, network-ssd-io-m3 93 28,000/5,600 110/82

To increase the maximum IOPS and bandwidth values and make throttling less likely, expand the storage when updating your cluster.

If you are using the network-hdd storage, consider switching to network-ssd or network-ssd-nonreplicated by restoring the cluster from a backup.

Connection

Can I connect to individual ClickHouse® hosts?

Yes. You can connect to ClickHouse® cluster hosts:

  • Using the HTTPS interface:

    • Via an encrypted SSL connection on port 8443.
    • Without encryption on port 8123.

  • Using the command-line client:

    • Via an encrypted SSL connection on port 9440.
    • Without encryption on port 9000.

SSH connections are not supported.

Why cannot I connect to a host from the internet?

Most likely, no public access is enabled for your cluster, so you can only connect to it from a VM in Yandex Cloud. You can only request public access when creating a new host in your cluster.

How do I connect to a non-public host in Yandex Cloud?

Connect to a host from a Yandex Cloud VM residing in the same cloud network, or add a new publicly accessible host to the cluster and use it to connect to the non-public host.

Can I connect to a public cluster without SSL?

No. You can only connect to public hosts over SSL. For more information, see this guide.

Why do I get an UNEXPECTED_PACKET_FROM_SERVER error when trying to connect?

Here is the full text of the error:

Code: 102. DB::NetException:
Unexpected packet from server <host_FQDN>.mdb.yandexcloud.net:9440
(expected Hello or Exception, got Unknown packet)

This error occurs when you try to connect to a ClickHouse® host on port 9440 without encryption. You can only connect on port 9440 over an encrypted SSL connection.

Make sure to specify the --secure parameter when connecting on port 9440.

To learn more about connection methods, see Connecting to a ClickHouse® cluster.

Can I connect to cluster hosts over SSH or get superuser privileges on hosts?

You cannot connect to hosts via SSH. This is done for the sake of security and user cluster fault tolerance because direct changes inside a host can render it completely inoperable.

What should I do if I get a revocation check error when using PowerShell to obtain an SSL certificate?

Here is the full text of the error:

curl: (35) schannel: next InitializeSecurityContext failed: Unknown error (0x80092012)
The revocation function was unable to check revocation for the certificate

This means that the service was unable to verify the website certificate against the revocation list when trying to connect.

To fix this error:

  • Make sure your corporate network policies are not blocking the verification.

  • Run the following command with the --ssl-no-revoke parameter:

    mkdir -Force $HOME\.yandex; `
curl.exe https://storage.yandexcloud.net/cloud-certs/RootCA.pem `
  --ssl-no-revoke `
  --output $HOME\.yandex\RootCA.crt; `
curl.exe https://storage.yandexcloud.net/cloud-certs/IntermediateCA.pem `
  --ssl-no-revoke `
  --output $HOME\.yandex\IntermediateCA.crt; `
Import-Certificate `
  -FilePath $HOME\.yandex\RootCA.crt `
  -CertStoreLocation cert:\CurrentUser\Root; `
Import-Certificate `
  -FilePath $HOME\.yandex\IntermediateCA.crt `
  -CertStoreLocation cert:\CurrentUser\Root

Updating a cluster

How do I add a host to a cluster?

To add a host, follow this guide. You can also add new hosts to a cluster when creating a shard.

Can I set join_use_nulls to 1 using the CLI?

Yes. To do this, when creating a user or updating user settings, provide the required join_use_nulls value in --settings. Here is an example:

yc managed-clickhouse user update <username> \
  --cluster-name=<cluster_name> \
  --settings="join_use_nulls=1"

For more information, see this guide.

Will my cluster be unavailable during an update?

If your cluster has more than one host, there is no downtime while updating it, since the hosts are updated one by one. Only individual hosts are unavailable when the cluster is being restarted.

How do I change the time zone?

Change the ClickHouse® timezone or session_timezone setting by following this guide.

Will my cluster be unavailable when adding replicas?

Yes, the cluster will experience a short downtime during restart.

How do I grant read-only permissions to a user?

To do this, when creating or editing a user via the CLI, specify readonly=1 in --settings. Here is an example:

yc managed-clickhouse user update <username> \
  --cluster-name=<cluster_name> \
  --settings="readonly=1"

For more information, see this guide.

How do I increase the memory limit?

Update the user settings and set the required Max memory usage value.

Can I change a network and subnets?

No, you can only select a network and subnets for hosts when creating a cluster or restoring it from a backup.

How do I change the distribution of data across shards in a cluster?

In an existing cluster, you cannot change the location of data in shards.

Cluster parameter settings

How do I create a user to access a cluster from DataLens with read-only permissions?

Follow this guide to create a user with read-only permissions. With DataLens access option enabled in the cluster settings, Managed Service for ClickHouse® can connect to the cluster using the created user.

How do I grant a user permissions to create and delete tables or databases?

Go to the cluster settings, enable User management via SQL, and grant the user the appropriate permissions using the GRANT statement.

How do I find out the internal_replication setting value?

The internal_replication setting information is not available in Yandex Cloud interfaces or ClickHouse® system tables. The default setting value is true.

How do I increase the maximum amount of RAM to run a query?

If you do not have enough RAM to run a query, you will see the following error:

DB::Exception: Memory limit (total) exceeded:
would use 14.10 GiB (attempt to allocate chunk of 4219924 bytes), maximum: 14.10 GiB.
(MEMORY_LIMIT_EXCEEDED), Stack trace (when copying this message, always include the lines below)

To increase the maximum amount of RAM, use the Max memory usage parameter.

If user management via SQL is enabled for the cluster, you can set the Max memory usage parameter:

  • For the current user session by running this query:

    SET max_memory_usage = <value_in_bytes>;

  • For all default users by creating a settings profile.

Why must a Managed Service for ClickHouse® cluster have three or five ZooKeeper hosts?

ZooKeeper uses the consensus algorithm: it keeps on running as long as most ZooKeeper hosts are healthy.

For example, if a cluster has two ZooKeeper hosts, then, should one of them stop, the remaining host will not form the majority, so the service will become unavailable. This means that a cluster with two ZooKeeper hosts is not fault-tolerant.

A cluster with three ZooKeeper hosts, on the other hand, is fault-tolerant. When one of its hosts is down or under maintenance, the cluster remains operational. Therefore, three is the minimum recommended number of ZooKeeper hosts per Managed Service for ClickHouse® cluster.

A cluster with four ZooKeeper hosts has no advantages over a three-host cluster: it will also remain operational if only one of its hosts fails. With two hosts down, the consensus is not met, so the service becomes unavailable.

A cluster with five ZooKeeper hosts is resilient enough to keep running without two of its hosts, three hosts out of five still forming the majority. This is why this cluster is easier to maintain than a three-host cluster. Even if one host out of five is under maintenance or restarting, the cluster remains fault-tolerant, i.e., it can lose one more host and still be operational.

Usually, adding more than five ZooKeeper hosts to a cluster is not feasible. The more ZooKeeper hosts, the longer their interaction times, and therefore the slower the service.

Thus, we recommend creating three or five ZooKeeper hosts per Managed Service for ClickHouse® cluster.

Moving and restoring a cluster

How are ClickHouse® databases backed up?

Backups are created every 24 hours and retained for seven days. You can only restore data as of the backup creation time.

Are database host backups enabled by default?

Yes, backups are enabled by default. For ClickHouse®, a full backup is performed once a day with the possibility to restore it to any saved backup.

When does a backup run? Is a database cluster available during backups?

When creating or updating a cluster, you can set the backup start window. The default value is 22:00 - 23:00 UTC (Coordinated Universal Time).

Clusters remain fully available during the backup window.

How many backups does Managed Service for ClickHouse® store? For how long?

The size and number of backups are not limited. Automatically created backups are retained for seven days, while manually created ones, indefinitely.

Can I delete a backup?

Yes, if you created it manually. To delete a backup, follow this guide.

Can I change the automatic backup retention period?

You can set the retention period for automatic backups when creating or updating a cluster.

What does a daily backup include?

Backups contain data solely for the MergeTree engine family. For other engines, backups only contain table schemas. For more information, see Backups.

Why does it take a long time to restore a cluster from a backup?

The approximate average speed of restoring a cluster from a backup is 100 Mbps. The recovery time may vary significantly depending on the host class and nature of the database data.

How do I move an existing ClickHouse® cluster to Yandex Cloud?

Use Yandex Data Transfer.

Can I restore a shard from a backup into a shard in an existing cluster?

This option is not currently supported.

However, you can restore your shard from a backup to a new ClickHouse® cluster and transfer data from that cluster into an existing one. To do this, explore the options below:

Monitoring and logs

What metrics and processes can be monitored?

For all DBMS types, you can monitor:

  • CPU, memory, network, or disk usage, in absolute terms.
  • Memory, network, and disk usage as a percentage of the set limits for the relevant cluster host class.
  • Amount of data in a database cluster and the remaining free space in your data storage.

For all database hosts, you can monitor metrics specific to their DBMS type. For example, for PostgreSQL, you can monitor:

  • Average query execution time.
  • Number of queries per second.
  • Number of errors in logs, and more.

You can monitor metrics with a minimum granularity of five seconds.

How is log storage billed?

Logs of any level are written to a disk's system partition (with 20 GB allocated) and are not charged separately. The size of the logs only affects the frequency of their rotation.

What is the retention period for logs?

Cluster logs are stored for 30 days.

How do I monitor free storage space on ZooKeeper hosts?

Follow the steps in this guide to monitor the host state or set up alerts.

How do I monitor space taken up by data in hybrid storage?

Use the ch_s3_disk_parts_size metric in Yandex Monitoring. It shows the amount of space used by MergeTree table parts in Object Storage. The metric is only available for Managed Service for ClickHouse® clusters with hybrid storage configured. To learn more on how to run a query with a metric, see this tutorial.

How do I set up an alert that triggers as soon as a certain percentage of disk space is used up?

Create an alert for the disk.used_bytes metric in Yandex Monitoring. This metric shows the disk space usage in the Managed Service for ClickHouse® cluster.

For disk.used_bytes, use notification thresholds. Their recommended values are as follows:

  • Alarm: 95% of disk space
  • Warning: 80% of disk space

Thresholds are set in bytes only. For example, the recommended values for a 100 GB disk are as follows:

  • Alarm: 102,005,473,280 bytes (95%)
  • Warning: 85,899,345,920 bytes (80%)

ClickHouse® is a registered trademark of ClickHouse, Inc.

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