[Yandex Cloud documentation](../../index.md) > [Yandex Managed Service for ClickHouse®](../index.md) > FAQ > General questions

# General questions about Managed Service for ClickHouse®


* [What is Managed Service for ClickHouse®?](#what-is)

* [What is ClickHouse® used for? Which DBMS should I select?](#why-ch)

* [What is the role of Managed Service for ClickHouse® in database management and maintenance?](#services)

* [When to use Managed Service for ClickHouse® and when database VMs?](#mdb-advantage)

* [What is a database host and database cluster?](#what-is-cluster)

* [How do I get started with Managed Service for ClickHouse®?](#quickstart})

* [How many database hosts can there be in a cluster?](#how-many-hosts)

* [How can I access a running database host?](#db-access)

* [How many clusters can I create within a single cloud?](#db-limit)

* [How are database clusters maintained?](#service-window)

* [How do I edit external dictionaries?](#external-dict)

* [Which ClickHouse® version does Managed Service for ClickHouse® use?](#dbms-version)

* [Which ClickHouse® version should I choose?](#choose-version)

* [What happens when a new DBMS version is released?](#new-version)

* [What happens when a DBMS version becomes deprecated?](#dbms-deprecated)

* [How do you calculate usage cost for a database host?](#db-cost)

* [How much does it cost to use my cluster?](#cluster-cost)

* [How can I change the computing resources and storage size for a database cluster?](#resources-change)

* [How can I fix the no permission error when attaching a service account to a cluster?](#attach-service-account)

* [What block size is used on the cluster disks?](#block-size)

* [Does the service comply with the Russian Federal Law 152-FZ on personal data?](#fz-152)

* [How do I get the logs of my activity in the Yandex Cloud services?](#logs)

#### What is Managed Service for ClickHouse®? {#what-is}

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 computing power and dedicated storage capacity for your databases as needed.
- Get database logs.

Managed Service for ClickHouse® handles the heavy lifting of ClickHouse® infrastructure management:
- Monitors your resource consumption.
- Performs automated database backups.
- Ensures [high availability](../concepts/high-availability.md) through automatic failover to standby replicas.
- Keeps your database software up-to-date.

You can work with a Managed Service for ClickHouse® database cluster the same way as 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? {#why-ch}

ClickHouse® is designed primarily for analytics (OLAP) and only supports adding and reading data. You can update data but with [certain limitations](https://stackoverflow.com/questions/37901642/updating-data-in-clickhouse). For other purposes, you might want to use another DBMS.

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

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](../../overview/concepts/geo-scope.md), with automatic failover to a standby replica if a failure occurs.

Be mindful of what is managed by the service and what, by the Yandex Cloud customer. Understanding these zones of control makes you an efficient user of cloud resources and helps avoid potential database-related issues. For more information, see [Zones of control between managed database (MDB) service users and Yandex Cloud](../../overview/concepts/mdb-responsibilities.md).

#### When to use Managed Service for ClickHouse® and when to use database VMs? {#mdb-advantage}

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? {#what-is-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®? {#quickstart}

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](../concepts/instance-types.md) 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 details, see [Getting started](../quickstart.md).

#### How many database hosts can a cluster contain? {#how-many-hosts}


The minimum number of hosts in a cluster depends on the following:
    
  * [Storage type](../concepts/storage.md):

    * 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](../concepts/sharding.md).


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

For more information, see [Quotas and limits](../concepts/limits.md).

#### How can I access a running database host? {#db-access}

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

Learn more about connecting to clusters in [this guide](../operations/connect/index.md).

#### How many clusters can I create within a single cloud? {#db-limit}

To learn more about technical and organizational limitations of MDB, see [Quotas and limits](../concepts/limits.md).

#### How are database clusters maintained? {#service-window}

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 tasks.

For more information, see [Maintenance](../concepts/maintenance.md).

#### How do I edit external dictionaries? {#external-dict}

To rename a dictionary, run this query:

```sql
RENAME DICTIONARY <dictionary_name> TO <new_name>
```

For other changes, use the [update](../api-ref/Cluster/update.md) API method.

#### Which ClickHouse® version does Managed Service for ClickHouse® use? {#dbms-version}

Managed Service for ClickHouse® uses multiple latest stable versions of ClickHouse®. For more information, see [ClickHouse® versioning policy](../concepts/update-policy.md).

#### Which ClickHouse® version should I choose? {#choose-version}

We recommend the latest available LTS version of ClickHouse®. For more information, see [ClickHouse® versioning policy](../concepts/update-policy.md).

#### What happens when a new DBMS version is released? {#new-version}

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

Owners of affected database clusters get advance notice of the upcoming maintenance schedule and database availability. 

#### What happens when a DBMS version becomes deprecated? {#dbms-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.

For clusters with a deprecated DBMS version, there is no option to create new hosts or restore from backups. Clusters running a deprecated ClickHouse® version are updated according to the [versioning policy](../concepts/update-policy.md).

Owners of affected database clusters get advance notice of upcoming maintenance and database availability.

#### How do you calculate usage cost for a database host? {#db-cost}

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. Backup storage exceeding this limit is charged according to our [pricing policy](../pricing.md).
- 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](../pricing.md).

#### How much does it cost to use my cluster? {#cluster-cost}

In the [management console](https://console.yandex.cloud), navigate to the folder dashboard, select **Managed Service for&nbsp;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 the [pricing policy](../pricing.md).

#### How can I change the computing resources and storage size for a database cluster? {#resources-change}

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? {#attach-service-account}

#### How can I fix the no permission error when connecting a service account to the cluster? {#attach-service-account}

Error message:

```text
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](../../iam/operations/roles/grant.md) your Yandex Cloud account the [iam.serviceAccounts.user](../../iam/security/index.md#iam-serviceAccounts-user) role or higher.

#### What block size is used on the cluster disks? {#block-size}

[Block](https://en.wikipedia.org/wiki/Block_(data_storage)) size for all disk types is 4 KB.

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

Yes, it does. You can read the full security audit conclusion [here](https://storage.yandexcloud.net/yc-compliance/conformance_en_pdp.pdf).

#### Can I get logs of my operations in Yandex Cloud? {#logs}

Yes, you can request information about operations with your resources from Yandex Cloud logs. Do it by contacting [support](https://center.yandex.cloud/support).

_ClickHouse® is a registered trademark of [ClickHouse, Inc](https://clickhouse.com)._