Manual snapshot beforeswitch for preprod-300 RDS stuck at 40% for several hours

The issue you're experiencing with your RDS snapshot being stuck at 40% for several hours is not uncommon and can occur for various reasons, even when your database metrics show low activity.

While there isn't a specific known issue with RDS manual snapshots in ap-south-1a mentioned in the available information, snapshot creation can sometimes take longer than expected due to several factors:

1. Database size: Even with low current activity, if your database is large, the snapshot process can take considerable time.

2. Consistency checks: AWS performs consistency checks during snapshot creation, which can extend the process time compared to manual snapshots.

3. Background processes: The snapshot process might be competing with system resources even if your visible metrics appear low.

4. Storage type considerations: While you're using gp3 storage, the snapshot process still needs to read all data blocks.

Possible workarounds:

1. Continue waiting: In some cases, snapshots that appear stuck may eventually complete. There's no specific time limit for snapshot creation.

2. Cancel and retry: If waiting isn't an option, you could consider canceling the current snapshot attempt and initiating a new one, preferably during a period of even lower activity.

3. Schedule snapshots during off-peak hours: For future snapshots, scheduling them during periods of minimal database activity can help reduce creation time.

4. Check CloudWatch logs: Review any relevant logs that might provide additional insights into what's happening with the snapshot process.

The good news is that your database remains fully operational during this process, as snapshot creation doesn't impact database availability or performance significantly.
Sources
Disable pre Upgrade system snapshot | AWS re:Post
Troubleshoot long-running or stuck snapshots in OpenSearch Service | AWS re:Post