MMON & MMNL (Manageability Monitor Processes)

Manageability Monitor Process (MMON) and Manageability Monitor Lite Process (MMNL)

The Eyes That Watch Performance 👀

🧠 What Are MMON & MMNL?

MMON and MMNL are background processes that monitor and manage database performance through the Automatic Workload Repository (AWR) and Active Session History (ASH). Together, they enable Oracle to detect problems, issue alerts, and support self-tuning.

🔧 Responsibilities of MMON & MMNL

ProcessRoleWhat It Does
🧠 MMONAWR ManagerCollects SGA stats, creates snapshots every 60 min, runs ADDM analysis, and raises performance alerts.
🌐 MMNLASH ManagerSamples active sessions every second, stores in ASH buffer, and periodically flushes to DBA_HIST_ACTIVE_SESS_HISTORY.

🗂️ Where the Data Lives

  • 📦 AWR: Located in the SYSAUX tablespace, stores long-term performance history.
  • 🔁 ASH Buffer: In-memory ring buffer, holds recent session activity.
  • 🔄 Flush Behavior: MMNL flushes 1 in 10 entries when ASH fills or on MMON snapshot.

💡 Why They Matter

  • 🧩 Help diagnose slow queries and resource bottlenecks.
  • ⚠️ Automatically raise alerts on metric thresholds.
  • 🔄 Enable ADDM, AWR Reports, and tuning tools.
  • 📉 Help in trend analysis and capacity planning.

🛠️ Technical Notes

  • Both run as threads or OS processes.
  • They also operate on Oracle ASM instances.
  • AWR snapshots can be created per PDB or at CDB root level.

📘 Tip of the Day:
Want to fine-tune snapshot frequency? Adjust the AWR_SNAPSHOT_TIME to align with your workload’s behavior — more frequent during peak hours, less during idle times.

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