[Yandex Cloud documentation](../../index.md) > [Yandex Managed Service for Valkey™](../index.md) > Concepts > Resource relationships

# Resource relationships in Yandex Managed Service for Valkey™



Valkey™ is a high-performance in-memory DBMS for storing key-value data. With Yandex Managed Service for Valkey™, you can easily create high-availability Valkey™ host clusters.

Yandex Cloud is an active contributor to both the core Valkey™ project and its [custom implementations](update-policy.md#compatibility-table). Such deep involvement allows the Yandex Managed Service for Valkey™ team to:

* Ensure high compatibility through a deep understanding of Valkey™‘s internal structure.
* Continuously improve performance, reliability, and security of custom implementations.
* Where applicable, leverage a more recent codebase for target version compatibility, thus delivering the benefits of latest releases without a target version upgrade.

Yandex Managed Service for Valkey™ provides extended [support](update-policy.md) for Valkey™ versions backed by the DBMS version [compatibility guarantee](#compatibility-warranty).

## Yandex Managed Service for Valkey™ resources {#resources}

The main entity in Yandex Managed Service for Valkey™ is a _database cluster_.

Each cluster consists of one or multiple _database hosts_, which are virtual machines with deployed DBMS servers. Cluster hosts may reside in different availability zones and even different availability regions. You can learn more about Yandex Cloud geography in the [Platform overview](../../overview/concepts/geo-scope.md) section.

[The high availability of a Yandex Managed Service for Valkey™ cluster](high-availability.md) depends on the number and placement of its hosts, replication settings, and other cluster parameters.

When creating a cluster, specify:
* _Host class_: VM template for deploying cluster hosts. For a list of available host classes and their specs, see [Host classes](instance-types.md).

* _Environment_: Environment where the cluster will be deployed:
   * `PRODUCTION`: For stable versions of your applications.
   * `PRESTABLE`: For testing purposes. The prestable environment is similar to the production environment and likewise covered by an SLA, but it is the first to get new features, improvements, and bug fixes. In the prestable environment, you can test new versions for compatibility with your application.

{% note info %}

The amount of memory allocated to a host also depends on the `maxmemory` configuration parameter for Valkey™ hosts: the maximum amount of data equals 75% of available memory. For example, for a host class with 8 GB RAM, the `maxmemory` value will be 6 GB.

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You can access a cluster created in a folder from any VM in the same cloud network. For more information about how the network works, see [this Virtual Private Cloud guide](../../vpc/index.md).


{% note alert %}

The service can automatically access the system and diagnostic information of your databases to render monitoring charts and maintain your cluster health. It never accesses or uses the data you entered into the database manually.

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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).

## Version compatibility guarantee {#compatibility-warranty}

Yandex Managed Service for Valkey™ does not provide its users with a particular Valkey™ version, but rather a service with _guaranteed compatibility_ for specific Valkey™ versions. For each [Yandex Cloud implementation](update-policy.md#compatibility-table) compatible with a certain Valkey™ version, Yandex Managed Service for Valkey™ guarantees:

* Full backward compatibility with the target version’s API and features.
* Support for all commands and protocols of the original version.
* Correct operation of existing user applications without the need to implement any changes.
* Extended support periods that match or exceed the official lifecycle of the original Valkey™ version.

![test-versions-compatibility1](../../_assets/managed-valkey/test-versions-compatibility1.svg)

For example, a DBMS version **compatible with Valkey™ 7.2** delivers:

* **Modern Valkey™ version** (`8.1`) with all its benefits in terms of performance, security, and features.
* **Compatibility mode** with settings for full backward compatibility and **guaranteed compatibility** with applications built for version `7.2`.

For more information on Valkey™ version compatibility, see [Version compatibility](update-policy.md#compatibility-table).

### Version compatibility testing {#compatibility-testing}

To verify version compatibility, we use comparative testing where the same test scenarios are executed simultaneously on both the Valkey™ target version and the Yandex Cloud implementation. If the results are identical, the Yandex Cloud implementation is considered compatible.

![test-versions-compatibility2](../../_assets/managed-valkey/test-versions-compatibility2.svg)

Our test scenarios cover critical Valkey™ behaviors:

* Commands and protocol: Correct command execution and [RESP](https://valkey.io/topics/protocol/) compliance.
* Data structures: Behavior of all data types, including `strings`, `hashes`, `lists`, `sets`, `sorted sets`, `streams`, etc.
* Error handling: Identical responses to invalid requests.
* Configuration: Support for target version configuration options.
* [Pub/Sub](https://valkey.io/topics/pubsub/), transactions, and scripts: Reliable performance in complex interactions.

Before deployment, every new Yandex Cloud implementation of a Valkey™ version must undergo a full suite of compatibility tests with the target version. Clusters are [updated](update-policy.md#update-policy) and migrated to the new implementation only after all tests have been completed successfully.

{% note tip %}

If specific Valkey™ use cases are critical to your application, [contact](https://center.yandex.cloud/support) support to propose adding them to the Yandex Managed Service for Valkey™ compatibility test suite. Our team will review each request and expand the test suite with relevant use cases.

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