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27 lines
1.7 KiB
Markdown
27 lines
1.7 KiB
Markdown
# system.clusters {#system-clusters}
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Contains information about clusters available in the config file and the servers in them.
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Columns:
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- `cluster` (String) — The cluster name.
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- `shard_num` (UInt32) — The shard number in the cluster, starting from 1.
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- `shard_weight` (UInt32) — The relative weight of the shard when writing data.
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- `replica_num` (UInt32) — The replica number in the shard, starting from 1.
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- `host_name` (String) — The host name, as specified in the config.
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- `host_address` (String) — The host IP address obtained from DNS.
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- `port` (UInt16) — The port to use for connecting to the server.
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- `user` (String) — The name of the user for connecting to the server.
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- `errors_count` (UInt32) - number of times this host failed to reach replica.
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- `estimated_recovery_time` (UInt32) - seconds left until replica error count is zeroed and it is considered to be back to normal.
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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.
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**See also**
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- [Table engine Distributed](../../engines/table-engines/special/distributed.md)
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- [distributed_replica_error_cap setting](../../operations/settings/settings.md#settings-distributed_replica_error_cap)
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- [distributed_replica_error_half_life setting](../../operations/settings/settings.md#settings-distributed_replica_error_half_life)
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[Original article](https://clickhouse.tech/docs/en/operations/system_tables/clusters) <!--hide-->
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