ClickhouseReplicaErrors

ClickhouseReplicaErrors #

Critical replica errors detected, either all replicas are stale or lost.

Alert Rule
alert: ClickhouseReplicaErrors
annotations:
  description: |-
    Critical replica errors detected, either all replicas are stale or lost.
      VALUE = {{ $value }}
      LABELS = {{ $labels }}    
  runbook: https://srerun.github.io/prometheus-alerts/runbooks/clickhouse-internal/clickhousereplicaerrors/
  summary: ClickHouse Replica Errors (instance {{ $labels.instance }})
expr: ClickHouseErrorMetric_ALL_REPLICAS_ARE_STALE == 1 or ClickHouseErrorMetric_ALL_REPLICAS_LOST
  == 1
for: 0m
labels:
  severity: critical

Meaning #

The ClickhouseReplicaErrors alert is triggered when all replicas in a ClickHouse cluster are either stale or lost, indicating a critical issue with data consistency and availability. This alert is raised when the ClickHouseErrorMetric_ALL_REPLICAS_ARE_STALE or ClickHouseErrorMetric_ALL_REPLICAS_LOST metrics equal 1, indicating that replica errors have been detected.

Impact #

The impact of this alert is high, as it indicates a critical issue with data consistency and availability in the ClickHouse cluster. If left unaddressed, this issue can lead to:

  • Data loss or corruption
  • Inconsistent query results
  • Increased latency or errors in dependent applications
  • Potential data integrity issues

Diagnosis #

To diagnose the root cause of the ClickhouseReplicaErrors alert, follow these steps:

  1. Check the ClickHouse cluster logs for error messages related to replica synchronization or data consistency.
  2. Verify the status of each replica node in the cluster, checking for any nodes that are not responding or are lagging behind.
  3. Review recent changes to the ClickHouse configuration or schema, as these may have caused the replica errors.
  4. Check the network connectivity and latency between replica nodes, as high latency or connectivity issues can cause replica errors.
  5. Verify that the ClickHouseErrorMetric_ALL_REPLICAS_ARE_STALE and ClickHouseErrorMetric_ALL_REPLICAS_LOST metrics are accurate and not reporting false positives.

Mitigation #

To mitigate the ClickhouseReplicaErrors alert, follow these steps:

  1. Immediately investigate and address any underlying issues causing the replica errors, such as network connectivity problems or node failures.
  2. If a replica node is lagging behind, consider re-initializing the node or re-applying incremental backups to bring it up to date.
  3. If a replica node is not responding, consider replacing the node or restarting the ClickHouse service on the node.
  4. Review and adjust ClickHouse configuration settings, such as the replica_max_lag setting, to ensure optimal replica synchronization.
  5. Implement additional monitoring and logging to detect and alert on replica errors more quickly in the future.
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