Run EXPLAIN ANALYZE on all select queries and log the results. Definitely don't use this if performance matters...

explain_analyze.rb

if Rails.env.development?
  require 'active_record/connection_adapters/postgresql_adapter'

  class ActiveRecord::ConnectionAdapters::PostgreSQLAdapter
    def __explain_analyze(sql, command, *args)
      meth = "#{command}_without_explain_analyze".to_sym
      if /\A\s*SELECT/i.match(sql)
        newsql = "EXPLAIN ANALYZE #{sql}"
        plan = send(meth, newsql, *args).map { |row| row['QUERY PLAN'] }.join("\n")
        Rails.logger.debug("\e[1m\e[31mQUERY PLAN FOR: #{sql.strip};\n#{plan}\e[0m")
      end
      send(meth, sql, *args)
    end

    def execute_with_explain_analyze(sql, *args)
      __explain_analyze(sql, :execute, *args)
    end

    def exec_query_with_explain_analyze(sql, *args)
      __explain_analyze(sql, :exec_query, *args)
    end

    alias_method_chain :execute, :explain_analyze
    alias_method_chain :exec_query, :explain_analyze
  end
end