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

Example

  1. :) SELECT * FROM system.clusters LIMIT 2 FORMAT Vertical;
  1. Row 1:
  2. ──────
  3. cluster:                 test_cluster
  4. shard_num:               1
  5. shard_weight:            1
  6. replica_num:             1
  7. host_name:               clickhouse01
  8. host_address:            172.23.0.11
  9. port:                    9000
  10. is_local:                1
  11. user:                    default
  12. default_database:        
  13. errors_count:            0
  14. estimated_recovery_time: 0
  16. Row 2:
  17. ──────
  18. cluster:                 test_cluster
  19. shard_num:               1
  20. shard_weight:            1
  21. replica_num:             2
  22. host_name:               clickhouse02
  23. host_address:            172.23.0.12
  24. port:                    9000
  25. is_local:                0
  26. user:                    default
  27. default_database:        
  28. errors_count:            0
  29. estimated_recovery_time: 0
  31. 2 rows in set. Elapsed: 0.002 sec.

Original article