How to discover what is generating an SQL statement in your Rails log

Just spreading a really cool tip I came across. Ryan Bigg has this blog post showing how you can find out what is creating an SQL statement in your log. I was having a devil of a time figuring out where a particular callback was coming from and discovered his great post. Essentially you hook into ActiveSupport::Notifications and then put in logic in the regex piece to describe the query you are looking for. In this case I did this in development.rb:

  ActiveSupport::Notifications.subscribe('sql.active_record') do |_, _, _, _, details|  
   if details[:sql] =~ /UPDATE "answers" SET position =/  
    puts '*' * 50  
    puts caller.join("\n")  
    puts '*' * 50  
   end  
  end  

And then looked at the call stack to see where it was coming from. I could have output to the logger too. And I would not recommend doing this on Production.

A new gem to help monitor Postgres performance in standalone instances

I just released my own gem for querying Postgres Databases for performance issues. I had used Heroku PG Extras and the Go Boundless New Relic Postgres plugin previously. Each are excellent tools with a lot of overlap. The holes for each-- hosting on Heroku needed for PG Extras and the lack of visibility into the queries themselves on New Relic-- pushed me to write this gem. My aim is to build an engine on it that will display the stats in screens that can be plugged into an application. We'll see how that goes.

Using Puma on Heroku instead of Unicorn

A few years back I wrote about using Unicorn on Heroku along with Unicorn Worker Killer. Oyr need was to increase the number of web requests an app could handle on Heroku. Puma tested faster at the time but did not offer worker processes. You have to use threads and for an app that was never intended to be threaded running on Ruby MRI it was too much work to adjust. Puma has since added the concept of Worker Processes and, given the performance advantages found with Puma it made sense to install it. Still, I was used to some variability with Unicorn and wanted to replicate some of the same things. This article from Heroku offered most of the help I needed though I did reduce the default thread count from 5 to 1. Additionally the section on the use of the Rack Timeout gem was helpful though I wound up doing this so that I could adjust the timeout via environment variable:

 Rack::Timeout.timeout = 20 # seconds  

What I did not find was helpful instructions on queue length. Puma defaults to 1024 and the previously mentioned article from Heroku cautions strongly against altering that queue length. Still, from previous performance testing on Heroku sometimes a shorter queue length is warranted (DO YOUR OWN TESTING!). This blog post originally suggested altering the queue length but again he cautions against it on Heroku. If you find that a shorter queue length helps then it is a setting in the config/puma.rb file:

 backlog = Integer(ENV['PUMA_BACKLOG'] || 20)  
 bind "tcp://0.0.0.0:#{port}?backlog=#{backlog}"   

Good luck and Heroku on