Issue when opening multiple (10+?) screens

[eelcoj]

When you open multiple tabs (at least 10+?) in your app/site that have mata enabled, I found pages struggle: long loading times and time outs. This might less prevalent on beefier machines or maybe not.

Would love to see an investigation and possible solution with it. ❤️

[pieromachacuaycabrera-cyber]

This is a textbook case of Puma Thread Pool & ActiveRecord Connection Pool Exhaustion.

If mata uses Server-Sent Events (ActionController::Live), long-polling, or ActionCable to keep a persistent connection open per tab, it is checking out one Puma thread and one Database connection per tab.

By default, Rails ships with Puma configured to 5 threads, and the database.yml pool set to 5.
If you open 5 tabs, 100% of your Puma threads and DB connections are locked. The 6th tab will hang infinitely (time out) because there are no threads left to serve the request.

The Solution

If mata uses an ActionController::Live streaming endpoint, you must release the ActiveRecord connection manually before entering the blocking stream loop. Otherwise, the DB pool starves instantly.

class Mata::EventsController < ApplicationController
  include ActionController::Live

  def stream
    response.headers['Content-Type'] = 'text/event-stream'
    
    # 1. Load any DB records you need BEFORE releasing the connection
    @user = current_user
    
    # 2. RELEASE the database connection back to the pool
    ActiveRecord::Base.clear_active_connections!
    
    begin
      # 3. Enter the persistent streaming loop (now running without holding a DB lock)
      loop do
        response.stream.write("event: ping\ndata: {}\n\n")
        sleep 3
      end
    ensure
      response.stream.close
    end
  end
end

Action for End-Users

Even with the DB connection released, SSE ties up a Puma thread. You should document that users relying heavily on mata should increase their Puma threads count and pool in database.yml (e.g., to 15 or 25), or use a non-blocking server architecture like AnyCable if it's WebSocket-based.

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I hope this architectural insight saves you some debugging time! If you found my contribution helpful, I’d really appreciate a coffee/tip to support my open-source work: https://www.paypal.me/Asi150403