MySQL and MariaDB Open Files % Alert

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Use the Open Files % alert in Mini DBA to monitor MySQL and MariaDB instances and make this condition visible before it becomes a wider database incident.

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Alert Summary

Platform: MySQL and MariaDB
Alert category: Disk
Default enabled: true
Default evaluation frequency: Minute
Threshold label: % of open_files_limit
Unit: %

What Mini DBA Checks

Mini DBA describes this alert as: MySQL is approaching its open_files_limit. Running out can cause table, log, or temporary file operations to fail. The default evaluation frequency is Minute, so the alert is intended to be close enough to operational reality for live triage. Because duration is used, Mini DBA can avoid treating a single short spike as a full incident when the condition clears quickly.

Why This Alert Is Helpful

This alert protects storage and recovery capacity. It helps you find growth, retention, and backup conditions that can stop writes, break recovery objectives, or leave the server without enough working space for normal database activity.

When To Enable It

Enable it on any monitored MySQL and MariaDB instance where this condition would require an administrator to investigate or communicate with the application team. Tune noisy development systems after you have a short baseline.

Threshold Guidance

Threshold meaning: % of open_files_limit. Major threshold: 95 %. Minor threshold: 85 %. Comparison direction: "over". Duration is used, so prefer requiring the condition to persist before paging people for transient spikes. Use higher thresholds on batch-heavy, development, or intentionally bursty systems where brief pressure is expected. Use lower thresholds on latency-sensitive production systems, small instances with little headroom, and services with strict recovery or availability commitments.

Remediation For An Active Alert

Open the related Mini DBA page for the instance, compare the current value with the recent baseline, identify whether the change is caused by workload, configuration, host capacity, or maintenance, then record the corrective action in the incident notes.

Investigation Workflow

Confirm the alert is still active and note the first seen time, affected instance, and severity.
Review the current metric, the recent trend, and the affected database, login, host, or application in Mini DBA before changing configuration or ending sessions.
Compare the current value with the normal baseline for the same time of day or maintenance window.
Record the cause, corrective action, and whether thresholds or routing should be adjusted after the incident.

Avoiding Alert Noise

If the alert creates repeated noise, review whether it is enabled on the correct instances, whether maintenance windows are configured, and whether the minor and major routes match the real business impact. Keep enough history to prove the new setting before changing it broadly.