title_wip

[Edit this page](https://github.com/ClickHouse/ClickHouse/tree/master/docs/en/operations/system-tables/clusters.md)

Contains information about clusters available in the config file and the servers in them.

Columns:

- `cluster` ([String](/docs/sql-reference/data-types)) — The cluster name.
- `shard_num` ([UInt32](/docs/sql-reference/data-types)) — The shard number in the cluster, starting from 1.
- `shard_name` ([String](/docs/sql-reference/data-types)) — The name of the shard in the cluster.
- `shard_weight` ([UInt32](/docs/sql-reference/data-types)) — The relative weight of the shard when writing data.
- `internal_replication` ([UInt8](/docs/sql-reference/data-types)) — Flag that indicates whether this host is a part on ensemble which can replicate the data on its own.
- `replica_num` ([UInt32](/docs/sql-reference/data-types)) — The replica number in the shard, starting from 1.
- `host_name` ([String](/docs/sql-reference/data-types)) — The host name, as specified in the config.
- `host_address` ([String](/docs/sql-reference/data-types)) — The host IP address obtained from DNS.
- `port` ([UInt16](/docs/sql-reference/data-types)) — The port to use for connecting to the server.
- `is_local` ([UInt8](/docs/sql-reference/data-types)) — Flag that indicates whether the host is local.
- `user` ([String](/docs/sql-reference/data-types)) — The name of the user for connecting to the server.
- `default_database` ([String](/docs/sql-reference/data-types)) — The default database name.
- `errors_count` ([UInt32](/docs/sql-reference/data-types)) — The number of times this host failed to reach replica.
- `slowdowns_count` ([UInt32](/docs/sql-reference/data-types)) — The number of slowdowns that led to changing replica when establishing a connection with hedged requests.
- `estimated_recovery_time` ([UInt32](/docs/sql-reference/data-types)) — Seconds remaining until the replica error count is zeroed and it is considered to be back to normal.
- `database_shard_name` ([String](/docs/sql-reference/data-types)) — The name of the `Replicated` database shard (for clusters that belong to a `Replicated` database).
- `database_replica_name` ([String](/docs/sql-reference/data-types)) — The name of the `Replicated` database replica (for clusters that belong to a `Replicated` database).
- `is_shared_catalog_cluster` ([UInt8](/docs/sql-reference/data-types)) — Bool indicating if the cluster belongs to shared catalog.
- `is_active` ([Nullable(UInt8)](/docs/sql-reference/data-types)) — The status of the Replicated database replica (for clusters that belong to a Replicated database): 1 means 'replica is online', 0 means 'replica is offline', NULL means 'unknown'.
- `unsynced_after_recovery` ([Nullable(UInt8)](/docs/sql-reference/data-types)) — Indicates if a Replicated database replica has replication lag more than max\_replication\_lag\_to\_enqueue after creating or recovering the replica.
- `replication_lag` ([Nullable(UInt32)](/docs/sql-reference/data-types)) — The replication lag of the `Replicated` database replica (for clusters that belong to a Replicated database).
- `recovery_time` ([Nullable(UInt64)](/docs/sql-reference/data-types)) — The recovery time of the `Replicated` database replica (for clusters that belong to a Replicated database), in milliseconds.

**Example**

Query:

```
SELECT * FROM system.clusters LIMIT 2 FORMAT Vertical;
```

Result:

```
Row 1:
──────
cluster:                 test_cluster_two_shards
shard_num:               1
shard_name:              shard_01
shard_weight:            1
replica_num:             1
host_name:               127.0.0.1
host_address:            127.0.0.1
port:                    9000
is_local:                1
user:                    default
default_database:
errors_count:            0
slowdowns_count:         0
estimated_recovery_time: 0
database_shard_name:
database_replica_name:
is_active:               NULL

Row 2:
──────
cluster:                 test_cluster_two_shards
shard_num:               2
shard_name:              shard_02
shard_weight:            1
replica_num:             1
host_name:               127.0.0.2
host_address:            127.0.0.2
port:                    9000
is_local:                0
user:                    default
default_database:
errors_count:            0
slowdowns_count:         0
estimated_recovery_time: 0
database_shard_name:
database_replica_name:
is_active:               NULL
```

**See Also**

- [Table engine Distributed](/docs/engines/table-engines/special/distributed)
- [distributed\_replica\_error\_cap setting](/docs/operations/settings/settings#distributed_replica_error_cap)
- [distributed\_replica\_error\_half\_life setting](/docs/operations/settings/settings#distributed_replica_error_half_life)

Was this page helpful?