system.clusters

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

Columns:

cluster (String) — The cluster name.
shard_num (UInt32) — The shard number in the cluster, starting from 1.
shard_name (String) — The name of the shard in the cluster.
shard_weight (UInt32) — The relative weight of the shard when writing data.
internal_replication (UInt8) — Flag that indicates whether this host is a part on ensemble which can replicate the data on its own.
replica_num (UInt32) — The replica number in the shard, starting from 1.
host_name (String) — The host name, as specified in the config.
host_address (String) — The host IP address obtained from DNS.
port (UInt16) — The port to use for connecting to the server.
is_local (UInt8) — Flag that indicates whether the host is local.
user (String) — The name of the user for connecting to the server.
default_database (String) — The default database name.
errors_count (UInt32) — The number of times this host failed to reach replica.
slowdowns_count (UInt32) — The number of slowdowns that led to changing replica when establishing a connection with hedged requests.
estimated_recovery_time (UInt32) — Seconds remaining until the replica error count is zeroed and it is considered to be back to normal.
database_shard_name (String) — The name of the Replicated database shard (for clusters that belong to a Replicated database).
database_replica_name (String) — The name of the Replicated database replica (for clusters that belong to a Replicated database).
is_active (Nullable(UInt8)) — 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)) — 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)) — The replication lag of the Replicated database replica (for clusters that belong to a Replicated database).
recovery_time (Nullable(UInt64)) — 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