Fix: ActiveRecord::ConnectionTimeoutError (MAYBE-RAILS-D0)

[revise-dev]

The ActiveRecord::ConnectionTimeoutError occurs when the application runs out of available database connections in the connection pool. The error indicates that all connections were in use for more than 5 seconds when a new connection was requested.

Looking at the application architecture:

1. Puma is configured to run with multiple threads (RAILS_MAX_THREADS=3 by default)
2. GoodJob background job processor is running with multiple queues:
   • 1 thread for latency_low
   • 2 threads for latency_low,latency_medium
   • 1 thread for latency_low,latency_medium,latency_high
   • 1 thread for catch-all queue
   • Plus additional threads for job listener, cron, and executor (3 threads)

The current pool size of 11 is insufficient because:

• Each Puma thread needs a connection (3 connections)
• GoodJob needs 8 connections (5 queue threads + 3 management threads)
• Additional connections may be needed for other concurrent operations

Increasing the pool size to 16 provides:

• 3 connections for Puma threads
• 8 connections for GoodJob
• 5 additional connections as buffer for peaks in concurrent activity

This change aligns with the application's concurrent processing needs while maintaining a reasonable buffer to prevent connection timeouts during normal operation.

Test plan:

1. Test concurrent web requests:

RSpec.describe "Database Connection Pool", type: :system do
  it "handles multiple concurrent requests without connection timeout" do
    allow(ActiveRecord::Base.connection_pool).to receive(:size).and_return(16)
    
    threads = 10.times.map do
      Thread.new do
        Account.transaction do
          Account.first
          sleep 0.5 # Simulate work
        end
      end
    end
    
    expect { threads.each(&:join) }.not_to raise_error
  end
end

2. Test background job concurrency:

RSpec.describe "Background Job Concurrency", type: :job do
  it "processes multiple jobs simultaneously without connection timeout" do
    jobs = 10.times.map do
      TestJob.perform_later
    end
    
    expect {
      GoodJob.perform_inline
    }.not_to raise_error
  end
end

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