Format and visualize AR queries using https://explain.dalibo.com

visualize_query.rb

class VisualizeQuery
  # Takes an AR relation (query), runs explain, and then uploads it to
  #   https://explain.dalibo.com for better visualization
  #
  # The query is also nicely formatted before visualizing using https://github.com/darold/pgFormatter
  # - This is run via `docker`
  # - If the placeholders are sensitive (for instance emails in a 'where' clause)
  #   you can pass `anonymize: true` and they'll be replaced with random strings

  method_object :query, [title: nil, anonymize: false]

  def call
    Faraday
      .new(url: 'https://explain.dalibo.com', headers: {'Content-Type' => 'application/json'})
      .post("/new", {
        plan: plan, 
        title: title, 
        query: formatted,
      }.compact.to_json)
      .headers['location']
  end

  private

  # This disables seq scan so that it forces the use of indices on smaller DBs
  #   to more accurately reflect production
  TEMPLATE = <<~EOS
    SET enable_seqscan = OFF;
    EXPLAIN (ANALYZE, COSTS, VERBOSE, BUFFERS, FORMAT JSON)
    %s
  EOS

  def formatted
    @formatted ||= %x(echo "#{query.to_sql}" | docker run --rm -a stdin -a stdout -i darold.net/pgformatter #{anonymize ? "-a": ""} -)
  end

  def plan
    @plan ||= ActiveRecord::Base.connection.execute(TEMPLATE % [query.to_sql])[0]['QUERY PLAN']
  end
end