# Use query cache in Managed ClickHouse®


Managed ClickHouse® provides a query cache mechanism that helps improve query performance
by caching query results.

## How it works

When the [ClickHouse query cache](https://clickhouse.com/docs/concepts/features/performance/caches/query-cache)
is enabled, the result of a `SELECT` query is computed once and stored in the cache.
Subsequent executions of the same query are served directly from the cache.

> [!IMPORTANT]
> By default, the Managed ClickHouse query cache is disabled for all `SELECT` queries.

## Why use it

Using query cache in your Managed ClickHouse services can help reduce latency and
resource consumption.

Key use case for the Managed ClickHouse query cache are the following:

- Performance enhancement: Reducing latency and load for frequently executed queries
- Analytical workloads: Using complex repetitive queries that involve high data aggregation

## Enable query cache

To enable the query cache for a query, set the `use_query_cache` setting for the query to `1`.
You can achieve this by appending `SETTINGS use_query_cache = 1` to the end of your query
using an SQL client (for example, the
[ClickHouse client](/product/dbaas/service-specific/clickhouse/how-to/connect-with-clickhouse-cli/)):

```sql
SELECT 1
SETTINGS use_query_cache = 1;
```

## Configure query cache

To configure the query cache settings, use an SQL client (for example, the
[ClickHouse client](/product/dbaas/service-specific/clickhouse/how-to/connect-with-clickhouse-cli/)) and
append a defined setting to your query, for example:

```sql
SELECT 1
SETTINGS use_query_cache = 1, query_cache_min_query_runs = 5000;
```

You can configure the following query cache settings:

- `enable_writes_to_query_cache`
- `enable_reads_from_query_cache`
- `query_cache_max_entries`
- `query_cache_min_query_runs`
- `query_cache_min_query_duration`
- `query_cache_compress_entries`
- `query_cache_squash_partial_results`
- `query_cache_ttl`
- `query_cache_share_between_users`

## Limitation

- Cached results are not invalidated or discarded when the underlying data (the result
  of a `SELECT` query) changes, which might cause returning stale results.
- Maximum query cache size: 64 MiB for each GiB of RAM (for example, 256 MiB for a 4-GiB
  service or 1 GiB for a 16-GiB service)
- Maximum number of query cache entries: 1024

## Related pages

- [Querying external data in Managed ClickHouse®](/product/dbaas/service-specific/clickhouse/overview/federated-queries/)
- [Query Managed ClickHouse® databases](/product/dbaas/service-specific/clickhouse/how-to/query-databases/)
- [Fetch query statistics for Managed ClickHouse®](/product/dbaas/service-specific/clickhouse/how-to/fetch-query-statistics/)
- [Create dictionaries in Managed ClickHouse®](/product/dbaas/service-specific/clickhouse/how-to/create-dictionary/)