Fix: ActiveRecord::ConnectionTimeoutError (MAYBE-RAILS-CX)

[revise-dev]

The ActiveRecord::ConnectionTimeoutError occurs because the application is running out of available database connections. This happens when all connections in the connection pool are in use and new requests cannot obtain a connection within the timeout period (5 seconds by default).

Looking at the configuration:

1. Puma is configured to use 3 threads per worker (default setting)
2. GoodJob is configured with 5 queue threads (1 + 2 + 1 + 1 from different queues)
3. Additional GoodJob threads for job listener, cron, and executor (3 threads)

Total required connections:

• Puma: 3 threads × 1 worker = 3 connections
• GoodJob queue threads: 5 connections
• GoodJob additional threads: 3 connections
• Total minimum required: 11 connections

The current pool size of 11 is exactly equal to the minimum required connections, leaving no buffer for occasional spikes or additional concurrent operations. It's best practice to provide some buffer capacity beyond the minimum required connections.

Changes to database.yml:

1. Increased the default pool size from 11 to 16, providing a buffer of 5 additional connections
2. Updated the comment to accurately reflect the connection requirements
3. Maintained the ability to override via DB_POOL_SIZE environment variable

This change ensures there are enough connections available during peak usage while maintaining the flexibility to adjust the pool size through environment variables if needed.

Test Additions:
Created a new test file to verify the connection pool configuration and behavior under load. The tests ensure:

1. The connection pool is configured with the correct size
2. The application can handle concurrent database operations
3. The pool size can be overridden via environment variables

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