> ## Documentation Index
> Fetch the complete documentation index at: https://clickhouse.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Large single-replica services

> Understand availability and scaling for large single-replica services in ClickHouse Cloud

Large single-replica services let you run a ClickHouse Cloud service with one compute replica while using the configurable compute resources available on the Scale and Enterprise tiers. Unlike fixed-size Basic tier services, their scaling behavior depends on the tier and hardware profile.

<h2 id="availability">
  Availability
</h2>

Large single-replica services are available on the Scale and Enterprise tiers. Basic tier services also use a single replica, but are fixed at `8 GiB` or `12 GiB` of total memory and don't support vertical or horizontal scaling.

On the Scale and Enterprise tiers, you can create a primary or secondary service with one replica without contacting support. Services in a [warehouse](/docs/products/cloud/features/infrastructure/warehouses) scale independently.

<h2 id="when-to-use-a-single-replica-service">
  When to use a single-replica service
</h2>

A large single-replica service can reduce compute costs for workloads that need more CPU or memory than a Basic tier service but don't require compute redundancy. It can also be useful for development, testing, batch processing, and other non-critical workloads.

<Warning>
  Single-replica services have reduced availability and aren't recommended for production workloads that require high availability. Use at least two replicas for high availability.
</Warning>

<h2 id="scaling">
  Scaling
</h2>

Vertical scaling behavior depends on the tier and hardware profile:

* Scale tier services and Enterprise tier services with standard `1:4` profiles support [vertical autoscaling](/docs/products/cloud/features/autoscaling/vertical). You can configure minimum and maximum CPU and memory resources in the Cloud Console.
* Enterprise tier services with custom profiles don't support vertical autoscaling or manual vertical scaling in the Cloud Console. Contact support for vertical resizing.

Scale and Enterprise tier services support [horizontal scaling](/docs/products/cloud/features/autoscaling/horizontal), so you can scale out to multiple replicas and scale back in to one replica.

<h2 id="service-limits">
  Service limits
</h2>

The Basic tier limits of `100` databases and `500` tables apply only to single-replica services in that tier. Single-replica services on the Scale and Enterprise tiers use the standard service guardrails. For details, see [Usage limits](/docs/products/cloud/guides/best-practices/usagelimits).