# Manage local cache for remote files in Managed ClickHouse®'s tiered storage


Managed ClickHouse®'s tiered storage features local on-disk cache for remote files for improved query performance and reduced latency.

To manage data, Managed ClickHouse's tiered storage uses local storage and remote storage.
When remote storage is used, Managed ClickHouse leverages a local on-disk cache to avoid
repeated remote fetches.

## How it works

When a query requires parts of a table stored in the remote tier, Managed ClickHouse
fetches the required parts from the remote storage. The fetched parts are automatically
stored in a local cache directory on the disk to avoid repeated downloads for subsequent
queries. For future queries, Managed ClickHouse checks the local cache first:

- If the data is found in the cache, it is read directly from the local disk.
- If the data is not found in the cache, it is fetched from the remote storage and stored
  in the local cache.

Local on-disk cache for remote files is enabled by default for Managed ClickHouse's
tiered storage. You can
[drop it](/product/dbaas/service-specific/clickhouse/how-to/local-cache-tiered-storage/#free-up-space) to
free up the space it occupies, or
[disable it per query](/product/dbaas/service-specific/clickhouse/how-to/local-cache-tiered-storage/#disable-the-cache).

## Prerequisites

-   At least one Managed ClickHouse service using tiered storage
-   Command line tool
    ([ClickHouse client](/product/dbaas/service-specific/clickhouse/how-to/connect-with-clickhouse-cli/))
    installed

## Disable the cache

To disable the local cache for a query, set the `enable_filesystem_cache` setting for the
query to `false`.
You can achieve this by appending `SETTINGS enable_filesystem_cache = false` 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 enable_filesystem_cache = false;
```

## Inspect the cache

Read the current size and entry count of the local cache from
`system.filesystem_cache`:

```sql
SELECT
    count() AS entries,
    formatReadableSize(sum(size)) AS cached
FROM system.filesystem_cache
```

The cache fills as queries read data from the object storage tier, so an empty result simply
means nothing has been read from that tier yet.

## Free up space

To drop the local cache and free up the used space, use the following cache command:

```sql
SYSTEM DROP FILESYSTEM CACHE 'remote_cache'
```

## What's next

-   [About tiered storage in Managed ClickHouse](/product/dbaas/service-specific/clickhouse/overview/clickhouse-tiered-storage/)
-   [Check data distribution between network-attached block storage and object storage](/product/dbaas/service-specific/clickhouse/how-to/check-data-tiered-storage/)
-   [Configure data retention thresholds for tiered storage](/product/dbaas/service-specific/clickhouse/how-to/configure-tiered-storage/)