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
- Table engine Distributed
- distributed_replica_error_cap setting
- distributed_replica_error_half_life setting
Example
:) SELECT * FROM system.clusters LIMIT 2 FORMAT Vertical;
Row 1:
──────
cluster: test_cluster
shard_num: 1
shard_weight: 1
replica_num: 1
host_name: clickhouse01
host_address: 172.23.0.11
port: 9000
is_local: 1
user: default
default_database:
errors_count: 0
estimated_recovery_time: 0
Row 2:
──────
cluster: test_cluster
shard_num: 1
shard_weight: 1
replica_num: 2
host_name: clickhouse02
host_address: 172.23.0.12
port: 9000
is_local: 0
user: default
default_database:
errors_count: 0
estimated_recovery_time: 0
2 rows in set. Elapsed: 0.002 sec.