https://chatgpt.com/share/684824d7-cf18-8005-b3b2-0bb650dbe15d
Hi [Manager’s Name],
As part of our effort to optimize RMAN backup performance (currently using 8 channels per database via Simpana), I’ve reviewed the current semaphore settings on our Oracle database servers. Our existing values are:
While these are functional, they are at risk of saturation during concurrent high-load operations across our 17 Oracle databases — especially when parallel RMAN backups are triggered.
🔧 Recommended Semaphore Settings
Based on the maximum processes parameter across the databases and safe provisioning for backup channels, I recommend increasing the semaphore parameters to the following:
📘 Technical Breakdown
| Parameter | Description | Recommended | Reason |
|---|---|---|---|
semmsl | Max semaphores per set (i.e., per process group) | 2048 | Should match or slightly exceed the highest processes value configured across all databases (some DBs have 1000+). |
semmns | Total number of semaphores available system-wide | 524288 | Should be ≥ sum of all processes × 2, to handle peak loads with backups, Data Guard, and job queues. |
semopm | Max operations per semop() call | 100 | Default is safe unless custom semaphore operations require more. |
semmni | Number of semaphore sets (IPC namespaces) | 64 | Roughly # of databases × 2 — gives us headroom for parallelism and maintenance windows. |
✅ Benefits
-
Prevents semaphore starvation during simultaneous backups
-
Reduces backup-related stalls or hangs due to IPC limitations
-
Aligns with Oracle best practices for high-concurrency environments
Please let me know if I can coordinate with the Unix team to schedule a sysctl.conf update and apply these settings. A reboot or sysctl -p will be required post-change to make them active.
Regards,
Daidipya Upalekar
Database Administrator
Oracle ACE
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