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83 lines
3.9 KiB
Markdown
83 lines
3.9 KiB
Markdown
---
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slug: /en/operations/system-tables/clusters
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---
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# 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](../../sql-reference/data-types/string.md)) — The cluster name.
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- `shard_num` ([UInt32](../../sql-reference/data-types/int-uint.md)) — The shard number in the cluster, starting from 1.
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- `shard_weight` ([UInt32](../../sql-reference/data-types/int-uint.md)) — The relative weight of the shard when writing data.
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- `replica_num` ([UInt32](../../sql-reference/data-types/int-uint.md)) — The replica number in the shard, starting from 1.
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- `host_name` ([String](../../sql-reference/data-types/string.md)) — The host name, as specified in the config.
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- `host_address` ([String](../../sql-reference/data-types/string.md)) — The host IP address obtained from DNS.
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- `port` ([UInt16](../../sql-reference/data-types/int-uint.md)) — The port to use for connecting to the server.
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- `is_local` ([UInt8](../../sql-reference/data-types/int-uint.md)) — Flag that indicates whether the host is local.
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- `user` ([String](../../sql-reference/data-types/string.md)) — The name of the user for connecting to the server.
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- `default_database` ([String](../../sql-reference/data-types/string.md)) — The default database name.
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- `errors_count` ([UInt32](../../sql-reference/data-types/int-uint.md)) — The number of times this host failed to reach replica.
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- `slowdowns_count` ([UInt32](../../sql-reference/data-types/int-uint.md)) — The number of slowdowns that led to changing replica when establishing a connection with hedged requests.
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- `estimated_recovery_time` ([UInt32](../../sql-reference/data-types/int-uint.md)) — Seconds remaining until the replica error count is zeroed, and it is considered to be back to normal.
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- `database_shard_name` ([String](../../sql-reference/data-types/string.md)) — The name of the `Replicated` database shard (for clusters that belong to a `Replicated` database).
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- `database_replica_name` ([String](../../sql-reference/data-types/string.md)) — The name of the `Replicated` database replica (for clusters that belong to a `Replicated` database).
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- `is_active` ([Nullable(UInt8)](../../sql-reference/data-types/int-uint.md)) — The status of the `Replicated` database replica (for clusters that belong to a `Replicated` database): 1 means "replica is online", 0 means "replica is offline", `NULL` means "unknown".
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- `name` ([String](../../sql-reference/data-types/string.md)) - An alias to cluster.
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**Example**
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Query:
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```sql
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SELECT * FROM system.clusters LIMIT 2 FORMAT Vertical;
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```
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Result:
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```text
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Row 1:
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──────
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cluster: test_cluster_two_shards
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shard_num: 1
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shard_weight: 1
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replica_num: 1
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host_name: 127.0.0.1
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host_address: 127.0.0.1
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port: 9000
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is_local: 1
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user: default
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default_database:
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errors_count: 0
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slowdowns_count: 0
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estimated_recovery_time: 0
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database_shard_name:
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database_replica_name:
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is_active: NULL
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Row 2:
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──────
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cluster: test_cluster_two_shards
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shard_num: 2
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shard_weight: 1
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replica_num: 1
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host_name: 127.0.0.2
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host_address: 127.0.0.2
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port: 9000
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is_local: 0
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user: default
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default_database:
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errors_count: 0
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slowdowns_count: 0
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estimated_recovery_time: 0
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database_shard_name:
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database_replica_name:
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is_active: NULL
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```
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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#distributed_replica_error_cap)
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- [distributed_replica_error_half_life setting](../../operations/settings/settings.md#distributed_replica_error_half_life)
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