ClickHouse/docs/en/operations/system-tables/clusters.md
Ivan Blinkov 7170f3c534
[docs] split aggregate function and system table references (#11742)
* prefer relative links from root

* wip

* split aggregate function reference

* split system tables
2020-06-18 11:24:31 +03:00

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Markdown

# system.clusters {#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](../../engines/table-engines/special/distributed.md)
- [distributed\_replica\_error\_cap setting](../../operations/settings/settings.md#settings-distributed_replica_error_cap)
- [distributed\_replica\_error\_half\_life setting](../../operations/settings/settings.md#settings-distributed_replica_error_half_life)