CassandraRepairBlockedTasks

CassandraRepairBlockedTasks #

Some Cassandra repair tasks are blocked

Alert Rule
alert: CassandraRepairBlockedTasks
annotations:
  description: |-
    Some Cassandra repair tasks are blocked
      VALUE = {{ $value }}
      LABELS = {{ $labels }}    
  runbook: https://srerun.github.io/prometheus-alerts/runbooks/criteo-cassandra-exporter/cassandrarepairblockedtasks/
  summary: Cassandra repair blocked tasks (instance {{ $labels.instance }})
expr: cassandra_stats{name="org:apache:cassandra:metrics:threadpools:internal:antientropystage:currentlyblockedtasks:count"}
  > 0
for: 2m
labels:
  severity: warning

Meaning #

The CassandraRepairBlockedTasks alert is triggered when the number of blocked Cassandra repair tasks exceeds 0 for more than 2 minutes. This indicates that there are issues with Cassandra’s repair process, which may lead to data inconsistencies and affect cluster performance.

Impact #

The impact of blocked Cassandra repair tasks can be significant, leading to:

  • Data inconsistencies: Unrepaired data can result in inconsistencies and affect query results
  • Performance degradation: Blocked repair tasks can slow down the cluster, causing slower query response times and decreased throughput
  • Increased risk of data loss: If repair tasks are blocked for an extended period, there is a higher risk of data loss in the event of a node failure

Diagnosis #

To diagnose the issue, follow these steps:

  1. Check the Cassandra cluster’s overall health and performance using metrics such as node uptime, CPU usage, and disk space
  2. Investigate the Cassandra logs for errors related to repair tasks, such as timeouts, exceptions, or configuration issues
  3. Verify that the Cassandra cluster is properly configured for repair, including settings such as replication_factor and repair_window
  4. Check for any external factors that may be affecting repair tasks, such as network connectivity issues or high load on the cluster

Mitigation #

To mitigate the issue, follow these steps:

  1. Check and adjust the Cassandra cluster’s configuration to ensure that it is properly set up for repair
  2. Investigate and resolve any underlying issues causing the blocked repair tasks, such as network connectivity problems or high load on the cluster
  3. Consider increasing the repair_window setting to allow more time for repair tasks to complete
  4. Monitor the cluster’s performance and adjust resources as needed to ensure that repair tasks can complete successfully
  5. Consider running a manual repair process to clear any blocked tasks and ensure data consistency
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