MongodbVirtualMemoryUsage #

High memory usage

alert: MongodbVirtualMemoryUsage
annotations:
  description: |-
    High memory usage
      VALUE = {{ $value }}
      LABELS = {{ $labels }}    
  runbook: https://srerun.github.io/prometheus-alerts/runbooks/dcu-mongodb-exporter/mongodbvirtualmemoryusage/
  summary: MongoDB virtual memory usage (instance {{ $labels.instance }})
expr: (sum(mongodb_memory{type="virtual"}) BY (instance) / sum(mongodb_memory{type="mapped"})
  BY (instance)) > 3
for: 2m
labels:
  severity: warning

Meaning #

The MongodbVirtualMemoryUsage alert is triggered when the ratio of virtual memory usage to mapped memory usage in a MongoDB instance exceeds 3. This means that the instance is using more virtual memory than actual physical memory, which can lead to performance issues and increased latency.

Impact #

If this alert is not addressed, it can lead to:

• Performance degradation: High virtual memory usage can cause MongoDB to slow down, leading to delayed query responses and decreased overall performance.
• Increased latency: As MongoDB relies more heavily on disk I/O to satisfy memory requests, latency will increase, causing issues for applications that rely on the database.
• Potential crashes: In extreme cases, excessive virtual memory usage can cause MongoDB to crash or become unresponsive.

Diagnosis #

To diagnose the issue, follow these steps:

1. Check the MongoDB instance’s memory usage: Use the mongodb_memory metric to examine the instance’s memory usage patterns. Identify any sudden spikes or increases in virtual memory usage.
2. Verify the memory allocation: Review the MongoDB configuration and ensure that the memory allocation is set correctly. Check if the instance is configured to use an excessive amount of virtual memory.
3. Inspect system resources: Check the system resources (CPU, RAM, and disk space) to ensure they are sufficient to support the MongoDB instance’s workload.
4. Analyze query patterns: Examine the query patterns and identify any resource-intensive queries that may be contributing to the high virtual memory usage.

Mitigation #

To mitigate the issue, follow these steps:

1. Adjust memory allocation: Review and adjust the MongoDB configuration to optimize memory allocation and reduce virtual memory usage.
2. Scale up the instance: Consider scaling up the MongoDB instance to increase the available physical memory and reduce the reliance on virtual memory.
3. Optimize queries: Optimize resource-intensive queries to reduce their memory footprint and minimize the load on the instance.
4. Monitor and adjust: Continuously monitor the instance’s memory usage and adjust the configuration as needed to prevent future occurrences of high virtual memory usage.