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ClickHouse/docs/en/operations/system-tables/clusters.md

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/en/operations/system-tables/clusters

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.

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

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

See Also