ActiveRecord slow query logging in Rails ... setup using: config.slow_query_log_threshold_in_ms = 500

slow_query_log.rb

require 'active_record/log_subscriber'

class SlowQueryLog < ActiveSupport::LogSubscriber

  if Rails.configuration.respond_to?(:slow_query_log_threshold_in_ms)
    if @@threshold = Rails.configuration.slow_query_log_threshold_in_ms
      @@threshold = @@threshold.to_i == 0 ? nil : @@threshold.to_i
    end
  else
    @@threshold = nil
  end

  def sql(event)
    return unless duration_ms = event.duration
    return if ! @@threshold || @@threshold > duration_ms

    payload = event.payload; name = payload[:name]

    return if name.eql? 'EXPLAIN'; return if name.eql? 'SCHEMA'

    if ( binds = payload[:binds] ) && ! binds.empty?
      binds = "  #{binds.map { |col,v| render_bind(col, v) }.inspect}"
    end

    log "#{name} (#{event.duration.round(1)}ms)  #{payload[:sql]}#{binds}"
  end

  def log(msg)
    logger = ActiveRecord::Base.logger
    logger && logger.warn("[slow-query] #{msg}")
  end

  private

  def render_bind(column, value) # from ActiveRecord::LogSubscriber
    return [nil, value] unless column
    if column.binary?
      value = value[:value] if value.is_a?(Hash)
      value = value ? "<#{value.bytesize} bytes of binary data>" : "<NULL binary data>"
    end
    [column.name, value]
  end

end

SlowQueryLog.attach_to :active_record

# config/initializer/slow_query_logger.rb
# frozen_string_literal: true

# rubocop:disable Metrics/ParameterLists
ActiveSupport::Notifications.subscribe('sql.active_record') do |_name, start, finish, _id, payload|
  duration = finish.to_f - start.to_f

  if duration >= 3.0
    Rails.logger.warn "slow query detected: #{payload[:sql]}, duration: #{duration}"
  end
end
# rubocop:enable Metrics/ParameterLists