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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_weight (UInt32) — The relative weight of the shard when writing data.
  • 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".
  • name (String) - An alias to cluster.

Example

Query:

SELECT * FROM system.clusters LIMIT 2 FORMAT Vertical;

Result:

Row 1:
──────
cluster: test_cluster_two_shards
shard_num: 1
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_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