> ## 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.

# Breaking Changes

Version-specific breaking changes for ClickHouse Private components. Review this page before upgrading.

***

## `helm/onprem-clickhouse-cluster` version `1.1.245` — Shared Catalog and Stateless Servers enabled by default

Starting with chart version `1.1.245`, `featureFlags.enableSharedCatalog` and `featureFlags.disableMetadataPersistentVolumes` default to `true`. New installations will use the [Shared](https://clickhouse.com/docs/engines/database-engines/shared) database engine and stateless Server nodes out of the box.

**New installations** require no action — the new defaults apply automatically.

**Existing installations not yet on Shared Catalog** must explicitly set the previous defaults to avoid an unintended migration on upgrade:

```yaml theme={null}
featureFlags:
  enableSharedCatalog: false
  disableMetadataPersistentVolumes: false
```

When you are ready to migrate, follow the [Migrate to Shared Catalog](/docs/cloud/clickhouse-private/how-to/migrate-to-shared-catalog) guide.

**Existing installations already on Shared Catalog** require no action — the new defaults match your current configuration.

***

## `helm/onprem-clickhouse-cluster` version `1.1.210`

Starting with chart version `1.1.210`, new config constraints are included by default. If you are using a ClickHouse server version **lower than 25.10**, you must exclude these constraints by adding the following to your server configuration:

```yaml theme={null}
server:
  excludeConfigConstraints:
    - allow_experimental_qbit_type
    - rewrite_in_to_join
    - allow_experimental_alias_table_engine
```

Without this configuration, ClickHouse will fail to start as these settings are not recognized by versions prior to 25.10.