Process Monitor (PMON)
🧠 What Is PMON?
The Process Monitor (PMON) is one of Oracle’s background processes, quietly ensuring that failed processes and sessions are cleaned up properly. It helps maintain the health of the instance by cleaning up after crashes or disconnections.
🧹 What PMON Does
| Component | Description |
|---|---|
| PMON 🔍 | Scans all processes regularly to detect abnormally terminated sessions. Delegates actual cleanup tasks to CLMN and runs as an OS-level process. |
| CLMN 🧼 | The Cleanup Main Process. Handles the actual cleanup of resources like memory, locks, and session entries. |
| CLnn (Workers) 🧑🔧 | Cleanup Worker Processes. CLMN assigns detailed cleanup tasks (like releasing resources) to these helper processes for efficiency and scalability. |
💻 Where PMON Runs
- 🛠️ Database Instances – Ensures session/process cleanup for terminated sessions.
- 💾 Oracle ASM Instances – Manages resource cleanup related to storage.
- 📡 Oracle ASM Proxy Instances – Same role as above, but for proxy-managed environments.
💡 DBA Tip of the Day
If you notice hanging sessions or resource contention, check PMON and related cleanup processes in the diagnostic logs. A sluggish PMON can indicate deeper system-level problems.