system.clusters

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Description

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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_shared_catalog_cluster (UInt8) — Bool indicating if the cluster belongs to shared catalog.
• 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.

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Example

SELECT * FROM system.clusters LIMIT 2 FORMAT Vertical;

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

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See also

• Table engine Distributed
• distributed_replica_error_cap setting
• distributed_replica_error_half_life setting