ClickHouse/docs/en/operations/system-tables/clusters.md
2020-12-03 13:47:56 -08:00

67 lines
2.5 KiB
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)
**Example**
```sql
:) SELECT * FROM system.clusters LIMIT 2 FORMAT Vertical;
```
```text
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.
```
[Original article](https://clickhouse.tech/docs/en/operations/system_tables/clusters) <!--hide-->