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ClickHouse/docs/en/operations/system-tables/clusters.md
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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_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.
  • user (String) — The name of the user for connecting to the server.
  • errors_count (UInt32) - number of times this host failed to reach replica.
  • estimated_recovery_time (UInt32) - seconds left until replica error count is zeroed and it is considered to be back to normal.

Please note that errors_count is updated once per query to the cluster, but estimated_recovery_time is recalculated on-demand. So there could be a case of non-zero errors_count and zero estimated_recovery_time, that next query will zero errors_count and try to use replica as if it has no errors.

See also

Original article