Allows to access all shards in an existing cluster which configured in `remote_servers` section without creating a [Distributed](../../engines/table-engines/special/distributed.md) table. One replica of each shard is queried.
Arguments can contain macros — substitutions in curly brackets. The substituted values are taken from the [macros](../../../operations/server-configuration-parameters/settings.md#macros) section of the server configuration file.
Example:
```sql
SELECT * FROM cluster('{cluster}', default.example_table);
Using the `cluster` and `clusterAllReplicas` table functions are less efficient than creating a `Distributed` table because in this case, the server connection is re-established for every request. When processing a large number of queries, please always create the `Distributed` table ahead of time, and do not use the `cluster` and `clusterAllReplicas` table functions.
The `cluster` and `clusterAllReplicas` table functions can be useful in the following cases:
- Accessing a specific cluster for data comparison, debugging, and testing.
- Queries to various ClickHouse clusters and replicas for research purposes.
- Infrequent distributed requests that are made manually.
Connection settings like `host`, `port`, `user`, `password`, `compression`, `secure` are taken from `<remote_servers>` config section. See details in [Distributed engine](../../engines/table-engines/special/distributed.md).
