The Open Files % alert notifies you when its configured condition is met on MySQL and MariaDB instances so you can investigate and respond.
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. Mini DBA evaluates this alert once a minute so changes are detected quickly. Because duration is used, Mini DBA can avoid treating a single short spike as a full incident when the condition clears quickly.
This alert shows that MySQL or MariaDB is approaching open_files_limit. Reaching the limit can prevent table, log, and temporary-file operations even when the filesystem still has free space.
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 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. For an over-threshold alert, decreasing a threshold makes that severity fire sooner; increasing it tolerates more load or pressure. Set the minor threshold as an early-warning level and the major threshold at the highest acceptable value for the service.
Review open file use, table cache settings, the database open_files_limit, and the operating-system file-descriptor limit. Correct leaks or oversized caches and raise limits together only after confirming operating-system capacity and service configuration.
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.