> ## Documentation Index > Fetch the complete documentation index at: https://private-7c7dfe99-revert-104359-revert-104251-parquet-single.mintlify.site/llms.txt > Use this file to discover all available pages before exploring further. # Cloud compatibility > This guide provides an overview of what to expect functionally and operationally in ClickHouse Cloud. This guide provides an overview of what to expect functionally and operationally in ClickHouse Cloud. While ClickHouse Cloud is based on the open-source ClickHouse distribution, there may be some differences in architecture and implementation. You may find this blog on [how we built ClickHouse Cloud](https://clickhouse.com/blog/building-clickhouse-cloud-from-scratch-in-a-year) interesting and relevant to read as background.

ClickHouse Cloud architecture

ClickHouse Cloud significantly simplifies operational overhead and reduces the costs of running ClickHouse at scale. There is no need to size your deployment upfront, set up replication for high availability, manually shard your data, scale up your servers when your workload increases, or scale them down when you're not using them — we handle this for you. These benefits come as a result of architectural choices underlying ClickHouse Cloud: * Compute and storage are separated and thus can be automatically scaled along separate dimensions, so you don't have to over-provision either storage or compute in static instance configurations. * Tiered storage on top of object store and multi-level caching provides virtually limitless scaling and good price/performance ratio, so you don't have to size your storage partition upfront and worry about high storage costs. * High availability is on by default and replication is transparently managed, so you can focus on building your applications or analyzing your data. * Automatic scaling for variable continuous workloads is on by default, so you don't have to size your service upfront, scale up your servers when your workload increases, or manually scale down your servers when you have less activity * Seamless hibernation for intermittent workloads is on by default. We automatically pause your compute resources after a period of inactivity and transparently start it again when a new query arrives, so you don't have to pay for idle resources. * Advanced scaling controls provide the ability to set an auto-scaling maximum for additional cost control or an auto-scaling minimum to reserve compute resources for applications with specialized performance requirements.

Capabilities

ClickHouse Cloud provides access to a curated set of capabilities in the open source distribution of ClickHouse. Tables below describe some features that are disabled in ClickHouse Cloud at this time.

Database and table engines

ClickHouse Cloud is a highly-available, replicated service by default, built on the [SharedMergeTree](/products/cloud/features/infrastructure/shared-merge-tree) table engine family. When you create a table with a standard MergeTree-family engine, Cloud automatically substitutes the corresponding `Shared*` engine. You don't add a `Shared` or `Replicated` prefix yourself. | You specify | Cloud uses | | ------------------------------ | ------------------------------------ | | `MergeTree` (or no engine) | `SharedMergeTree` | | `ReplacingMergeTree` | `SharedReplacingMergeTree` | | `SummingMergeTree` | `SharedSummingMergeTree` | | `AggregatingMergeTree` | `SharedAggregatingMergeTree` | | `CollapsingMergeTree` | `SharedCollapsingMergeTree` | | `VersionedCollapsingMergeTree` | `SharedVersionedCollapsingMergeTree` | | `GraphiteMergeTree` | `SharedGraphiteMergeTree` | `Replicated*` engines are converted to the same `Shared*` equivalents. The substitution is visible in `SHOW CREATE TABLE`, which reports the `Shared*` engine even though your statement specified the plain variant. The following table engines are also supported and used as written. The supported `MySQL` table engine is distinct from the unsupported `MySQL` database engine: * URL * View * MaterializedView * GenerateRandom * Null * Buffer * Memory * Deltalake * Hudi * MySQL * MongoDB * NATS * RabbitMQ * PostgreSQL * S3 * Kafka

Interfaces

ClickHouse Cloud supports HTTPS, native interfaces, and the [MySQL wire protocol](/concepts/features/interfaces/mysql). Support for more interfaces such as Postgres is coming soon.

Dictionaries

Dictionaries are a popular way to speed up lookups in ClickHouse. ClickHouse Cloud currently supports dictionaries from PostgreSQL, MySQL, remote and local ClickHouse servers, Redis, MongoDB and HTTP sources.

Federated queries

We support federated ClickHouse queries for cross-cluster communication in the cloud, and for communication with external self-managed ClickHouse clusters. ClickHouse Cloud currently supports federated queries using the following integration engines: * Deltalake * Hudi * MySQL * MongoDB * NATS * RabbitMQ * PostgreSQL * S3 Federated queries with some external database and table engines, such as SQLite, ODBC, JDBC, Redis, HDFS and Hive aren't yet supported.

User defined functions

User-defined functions in ClickHouse Cloud are in [public beta](/reference/functions/regular-functions/udf).

Settings behavior

**Important** UDFs in ClickHouse Cloud **don't inherit user-level settings**. They execute with default system settings. This means: * Session-level settings (set via `SET` statement) aren't propagated to UDF execution context * User profile settings aren't inherited by UDFs * Query-level settings don't apply within UDF execution

Experimental features

Experimental features are disabled in ClickHouse Cloud services to ensure the stability of service deployments.

Named collections

[Named collections](/concepts/features/configuration/server-config/named-collections) aren't currently supported in ClickHouse Cloud.

Operational defaults and considerations

The following are default settings for ClickHouse Cloud services. In some cases, these settings are fixed to ensure the correct operation of the service, and in others, they can be adjusted.

Operational limits

`max_parts_in_total: 10,000`

The default value of the `max_parts_in_total` setting for MergeTree tables has been lowered from 100,000 to 10,000. The reason for this change is that we observed that a large number of data parts is likely to cause a slow startup time of services in the cloud. A large number of parts usually indicate a choice of too granular partition key, which is typically done accidentally and should be avoided. The change of default will allow the detection of these cases earlier.

`max_concurrent_queries: 1,000`

Increased this per-server setting from the default of `100` to `1000` to allow for more concurrency. This will result in `number of replicas * 1,000` concurrent queries for the offered tier services. `1000` concurrent queries for Basic tier service limited to a single replica and `1000+` for Scale and Enterprise, depending on the number of replicas configured.

`max_table_size_to_drop: 1,000,000,000,000`

Increased this setting from 50GB to allow for dropping of tables/partitions up to 1TB.

System settings

ClickHouse Cloud is tuned for variable workloads, and for that reason most system settings aren't configurable at this time. We don't anticipate the need to tune system settings for most users, but if you have a question about advanced system tuning, please contact ClickHouse Cloud Support.

Advanced security administration

As part of creating the ClickHouse service, we create a default database, and the default user that has broad permissions to this database. This initial user can create additional users and assign their permissions to this database. Beyond this, the ability to enable the following security features within the database using Kerberos, LDAP, or SSL X.509 certificate authentication aren't supported at this time.

List of unsupported features

The following tables list features and self-managed procedures that are marked as unsupported in ClickHouse Cloud. Each entry names the specific unsupported capability, even when its source page also covers supported functionality.

Managed infrastructure and operations

| Unsupported capability | Documentation | | ------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------ | | Self-managed `ClickHouse Keeper` deployment and configuration | [Keeper guide](/guides/oss/deployment-and-scaling/keeper), [Secure ZooKeeper connections](/guides/oss/deployment-and-scaling/keeper/ssl-zookeeper) | | Manual TLS certificate provisioning and server configuration | [ACME provisioning](/concepts/features/security/tls/configuring-tls-acme-client), [TLS configuration](/concepts/features/security/tls/configuring-tls) | | Manual hot/warm/cold storage-tier configuration with `TTL` | [Guide](/concepts/features/operations/delete/ttl#implementing-a-hotwarmcold-architecture) | | Running self-managed hardware performance tests | [Guide](/concepts/features/performance/troubleshoot/performance-test) | | Applying self-managed operational recommendations | [Guide](/guides/oss/best-practices/tips) |

Authentication and security

| Unsupported capability | Documentation | | ------------------------------------ | -------------------------------------------------------------------------------------------------------------------------------------------------------- | | HTTP external authentication | [Reference](/concepts/features/security/external-authenticators/http) | | Kerberos external authentication | [Reference](/concepts/features/security/external-authenticators/kerberos) | | LDAP authentication and role mapping | [Configuration](/concepts/features/security/configuring-ldap), [Authenticator](/concepts/features/security/external-authenticators/ldap) | | X.509 certificate authentication | [User authentication](/concepts/features/security/ssl-user-auth), [External authenticator](/concepts/features/security/external-authenticators/ssl-x509) |

Interfaces and integrations

| Unsupported capability | Documentation | | ----------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | PostgreSQL wire-protocol interface | [Reference](/concepts/features/interfaces/postgresql) | | SSH interface with PTY | [Reference](/concepts/features/interfaces/ssh) | | `MaterializedPostgreSQL` replication engine | [ClickPipes guide](/integrations/clickpipes/postgres/connecting-to-postgresql#using-the-materializedpostgresql-database-engine), [Connector guide](/integrations/connectors/data-sources/postgres), [Database engine](/reference/engines/database-engines/materialized-postgresql), [Table engine](/reference/engines/table-engines/integrations/materialized-postgresql) | | ODBC integration and the `ODBC` table engine | [Integration guide](/integrations/connectors/data-ingestion/odbc-with-clickhouse), [Table engine](/reference/engines/table-engines/integrations/odbc) | | MinIO S3-compatible object-storage integration | [Guide](/integrations/connectors/data-ingestion/s3-minio) | | Tigris S3-compatible object-storage integration | [Guide](/integrations/connectors/data-ingestion/s3-tigris) |

Database and table engines

| Unsupported capability | Documentation | | -------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `MySQL` database engine | [Reference](/reference/engines/database-engines/mysql) | | `EmbeddedRocksDB` table engine | [Reference](/reference/engines/table-engines/integrations/embedded-rocksdb) | | `HDFS` table engine | [Reference](/reference/engines/table-engines/integrations/hdfs) | | `Hive` table engine | [Reference](/reference/engines/table-engines/integrations/hive) | | `JDBC` table engine | [Reference](/reference/engines/table-engines/integrations/jdbc) | | `Redis` table engine for federated queries | [Reference](/reference/engines/table-engines/integrations/redis) | | `SQLite` table engine | [Reference](/reference/engines/table-engines/integrations/sqlite) | | `TimeSeries` table engine | [Reference](/reference/engines/table-engines/integrations/time-series) | | `YTsaurus` table engine | [Reference](/reference/engines/table-engines/integrations/ytsaurus) | | `Log`-family table engines (`Log`, `StripeLog`, and `TinyLog`) | [Family overview](/reference/engines/table-engines/log-family), [`Log`](/reference/engines/table-engines/log-family/log), [`StripeLog`](/reference/engines/table-engines/log-family/stripelog), [`TinyLog`](/reference/engines/table-engines/log-family/tinylog) |

Dictionaries and server configuration

| Unsupported capability | Documentation | | ------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | Named collections and the `CREATE NAMED COLLECTION` and `ALTER NAMED COLLECTION` statements | [Overview](/concepts/features/configuration/server-config/named-collections), [Create](/reference/statements/create/named-collection), [Alter](/reference/statements/alter/named-collection) | | File-based dictionary configuration | [Reference](/reference/statements/create/dictionary#creating-a-dictionary-with-a-configuration-file) | | Embedded geobase dictionaries | [Reference](/reference/statements/create/dictionary/embedded) | | Local `YAMLRegExpTree` dictionary sources | [Layout guide](/reference/statements/create/dictionary/layouts/regexp-tree#use-regular-expression-tree-dictionary-in-clickhouse-open-source), [Source reference](/reference/statements/create/dictionary/sources/yamlregexptree) | | `YTsaurus` dictionary source | [Reference](/reference/statements/create/dictionary/sources/ytsaurus) | | Japanese tokenizer dictionaries configured on the server | [Reference](/reference/engines/table-engines/mergetree-family/textindexes#japanese-tokenizer-dictionary) |

Data formats and codecs

| Unsupported capability | Documentation | | -------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `CapnProto` format with server-side schema files | [Format reference](/reference/formats/CapnProto), [Guide](/guides/clickhouse/data-formats/binary#capn-proto) | | `Protobuf`, `ProtobufList`, and `ProtobufSingle` formats with server-side schema files | [Guide](/guides/clickhouse/data-formats/binary#protocol-buffers), [`ProtobufList`](/reference/formats/Protobuf/ProtobufList), [`ProtobufSingle`](/reference/formats/Protobuf/ProtobufSingle) | | Obsolete `ZSTD_QAT` and `DEFLATE_QPL` codecs | [`ZSTD_QAT`](/reference/statements/create/table#zstd_qat), [`DEFLATE_QPL`](/reference/statements/create/table#deflate_qpl) |

Functions and experimental features

| Unsupported capability | Documentation | | ------------------------------------------------------------------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | Experimental natural-language processing functions | [Reference](/reference/functions/regular-functions/nlp-functions) | | Experimental multi-statement transactions with commit and rollback | [Guide](/concepts/features/operations/insert/transactions#transactions-commit-and-rollback) | | Experimental transaction introspection functions | [`transactionID`](/reference/functions/regular-functions/other-functions#transactionID), [`transactionLatestSnapshot`](/reference/functions/regular-functions/other-functions#transactionLatestSnapshot), [`transactionOldestSnapshot`](/reference/functions/regular-functions/other-functions#transactionOldestSnapshot) | | Time-window functions for `WindowView` | [Reference](/reference/functions/regular-functions/time-window-functions) | | Experimental `WindowView` | [Reference](/reference/statements/create/view#window-view) | | WebAssembly user-defined functions | [Overview](/reference/functions/regular-functions/udf#webassembly-user-defined-functions), [Guide](/reference/functions/regular-functions/wasm_udf) | | Driver-based executable user-defined functions | [Reference](/reference/functions/regular-functions/udf#driver-based-executable-user-defined-functions) | | `filesystem` table function over server-local files | [Reference](/reference/functions/table-functions/filesystem) |

Administration and access control

| Unsupported capability | Documentation | | ---------------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------- | | Column-statistics operations with `ALTER TABLE` | [Reference](/reference/statements/alter/statistics) | | User impersonation with `EXECUTE AS` | [Reference](/reference/statements/execute_as) | | Table-engine-specific grants | [Grant](/reference/statements/grant#table-engine), [Server setting](/reference/settings/server-settings/settings/other#table_engines_require_grant) | | The `GRANT ALL` privilege shortcut | [Reference](/reference/statements/grant#all) | | Server shutdown with `SYSTEM SHUTDOWN` | [Reference](/reference/statements/system#shutdown) | | Starting and stopping background fetches with `SYSTEM` statements | [`SYSTEM STOP FETCHES`](/reference/statements/system#stop-fetches), [`SYSTEM START FETCHES`](/reference/statements/system#start-fetches) | | Starting and stopping background merges with `SYSTEM` statements | [`SYSTEM STOP MERGES`](/reference/statements/system#stop-merges), [`SYSTEM START MERGES`](/reference/statements/system#start-merges) | | Starting and stopping background `TTL` merges with `SYSTEM` statements | [`SYSTEM STOP TTL MERGES`](/reference/statements/system#stop-ttl-merges), [`SYSTEM START TTL MERGES`](/reference/statements/system#start-ttl-merges) |

Roadmap

We're evaluating demand for many other features in ClickHouse Cloud. If you have feedback and would like to ask for a specific feature, please [submit it here](https://console.clickhouse.cloud/support).