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Alert thresholds depend on the nature of your applications. Some queries may have arbitrary tolerance thresholds. Building an efficient monitoring platform takes time. 😉

JVM Prometheus Alert Rules

12 Prometheus alerting rules for JVM. Exported via java-client. These rules cover critical and warning conditions — copy and paste the YAML into your Prometheus configuration.

5.2. java-client (12 rules) 

wget https://raw.githubusercontent.com/samber/awesome-prometheus-alerts/refs/heads/master/dist/rules/jvm/jvm-exporter.yml
warning

5.2.1. JVM memory filling up

JVM memory is filling up (> 80%) 

- alert: JVMMemoryFillingUp
  expr: (sum by (instance)(jvm_memory_used_bytes{area="heap"}) / sum by (instance)(jvm_memory_max_bytes{area="heap"})) * 100 > 80 and sum by (instance)(jvm_memory_max_bytes{area="heap"}) > 0
  for: 2m
  labels:
    severity: warning
  annotations:
    summary: JVM memory filling up (instance {{ $labels.instance }})
    description: "JVM memory is filling up (> 80%)\n  VALUE = {{ $value }}\n  LABELS = {{ $labels }}"
warning

5.2.2. JVM non-heap memory filling up

JVM non-heap memory (metaspace/code cache) is filling up (> 80%) 

  # Many JVM configurations leave metaspace unbounded, in which case jvm_memory_max_bytes{area="nonheap"} is -1 and this alert will not fire.
  # The query filters out max_bytes <= 0 to avoid false negatives.
- alert: JVMNon-heapMemoryFillingUp
  expr: (sum by (instance)(jvm_memory_used_bytes{area="nonheap"}) / (sum by (instance)(jvm_memory_max_bytes{area="nonheap"}) > 0)) * 100 > 80
  for: 2m
  labels:
    severity: warning
  annotations:
    summary: JVM non-heap memory filling up (instance {{ $labels.instance }})
    description: "JVM non-heap memory (metaspace/code cache) is filling up (> 80%)\n  VALUE = {{ $value }}\n  LABELS = {{ $labels }}"
warning

5.2.3. JVM GC time too high

JVM is spending too much time in garbage collection (> 5% of wall clock time) 

- alert: JVMGCTimeTooHigh
  expr: sum by (instance)(rate(jvm_gc_collection_seconds_sum[5m])) > 0.05
  for: 5m
  labels:
    severity: warning
  annotations:
    summary: JVM GC time too high (instance {{ $labels.instance }})
    description: "JVM is spending too much time in garbage collection (> 5% of wall clock time)\n  VALUE = {{ $value }}\n  LABELS = {{ $labels }}"
critical

5.2.4. JVM threads deadlocked

JVM has deadlocked threads 

- alert: JVMThreadsDeadlocked
  expr: jvm_threads_deadlocked > 0
  for: 1m
  labels:
    severity: critical
  annotations:
    summary: JVM threads deadlocked (instance {{ $labels.instance }})
    description: "JVM has deadlocked threads\n  VALUE = {{ $value }}\n  LABELS = {{ $labels }}"
warning

5.2.5. JVM thread count high

JVM thread count is high (> 300), potential thread leak 

- alert: JVMThreadCountHigh
  expr: jvm_threads_current > 300
  for: 5m
  labels:
    severity: warning
  annotations:
    summary: JVM thread count high (instance {{ $labels.instance }})
    description: "JVM thread count is high (> 300), potential thread leak\n  VALUE = {{ $value }}\n  LABELS = {{ $labels }}"
warning

5.2.6. JVM threads BLOCKED

JVM has high number of BLOCKED threads, indicating lock contention 

- alert: JVMThreadsBLOCKED
  expr: jvm_threads_state{state="BLOCKED"} > 50
  for: 5m
  labels:
    severity: warning
  annotations:
    summary: JVM threads BLOCKED (instance {{ $labels.instance }})
    description: "JVM has high number of BLOCKED threads, indicating lock contention\n  VALUE = {{ $value }}\n  LABELS = {{ $labels }}"
warning

5.2.7. JVM old gen GC frequency

Frequent old/major GC cycles, indicating memory pressure 

  # This regex matches CMS, G1, and Parallel collector names. It will not match ZGC or Shenandoah cycle names.
  # Adjust the gc label filter if you use a different collector.
- alert: JVMOldGenGCFrequency
  expr: rate(jvm_gc_collection_seconds_count{gc=~".*old.*|.*major.*"}[5m]) > 0.3
  for: 5m
  labels:
    severity: warning
  annotations:
    summary: JVM old gen GC frequency (instance {{ $labels.instance }})
    description: "Frequent old/major GC cycles, indicating memory pressure\n  VALUE = {{ $value }}\n  LABELS = {{ $labels }}"
warning

5.2.8. JVM direct buffer pool filling up

JVM direct buffer pool is filling up (> 90%) 

- alert: JVMDirectBufferPoolFillingUp
  expr: (jvm_buffer_pool_used_bytes / jvm_buffer_pool_capacity_bytes) * 100 > 90 and jvm_buffer_pool_capacity_bytes > 0
  for: 5m
  labels:
    severity: warning
  annotations:
    summary: JVM direct buffer pool filling up (instance {{ $labels.instance }})
    description: "JVM direct buffer pool is filling up (> 90%)\n  VALUE = {{ $value }}\n  LABELS = {{ $labels }}"
warning

5.2.9. JVM objects pending finalization

JVM has objects pending finalization, potential memory leak 

- alert: JVMObjectsPendingFinalization
  expr: jvm_memory_objects_pending_finalization > 1000
  for: 5m
  labels:
    severity: warning
  annotations:
    summary: JVM objects pending finalization (instance {{ $labels.instance }})
    description: "JVM has objects pending finalization, potential memory leak\n  VALUE = {{ $value }}\n  LABELS = {{ $labels }}"
warning

5.2.10. JVM file descriptors exhaustion

JVM process is running out of file descriptors (> 90% used) 

  # process_open_fds and process_max_fds are generic metrics from the Prometheus client library, not JVM-specific.
  # This alert will also fire for Go, Python, or any process exposing these metrics.
- alert: JVMFileDescriptorsExhaustion
  expr: (process_open_fds / process_max_fds) * 100 > 90 and process_max_fds > 0
  for: 5m
  labels:
    severity: warning
  annotations:
    summary: JVM file descriptors exhaustion (instance {{ $labels.instance }})
    description: "JVM process is running out of file descriptors (> 90% used)\n  VALUE = {{ $value }}\n  LABELS = {{ $labels }}"
warning

5.2.11. JVM class loading anomaly

Rapid class loading detected, potential classloader leak 

- alert: JVMClassLoadingAnomaly
  expr: rate(jvm_classes_loaded_total[5m]) > 100
  for: 5m
  labels:
    severity: warning
  annotations:
    summary: JVM class loading anomaly (instance {{ $labels.instance }})
    description: "Rapid class loading detected, potential classloader leak\n  VALUE = {{ $value }}\n  LABELS = {{ $labels }}"
warning

5.2.12. JVM compilation time spike

Excessive JIT compilation time consuming CPU 

- alert: JVMCompilationTimeSpike
  expr: rate(jvm_compilation_time_seconds_total[5m]) > 0.1
  for: 5m
  labels:
    severity: warning
  annotations:
    summary: JVM compilation time spike (instance {{ $labels.instance }})
    description: "Excessive JIT compilation time consuming CPU\n  VALUE = {{ $value }}\n  LABELS = {{ $labels }}"

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