Contents

# frozen_string_literal: true

module WtActiverecordIndexSpy
  class QueryAnalyser
    # It analyses the result of an EXPLAIN query to see if any index is missing.
    module Mysql
      extend self

      ALLOWED_EXTRA_VALUES = [
        # https://bugs.mysql.com/bug.php?id=64197
        "Impossible WHERE noticed after reading const tables",
        "no matching row",
      ].freeze

      def analyse(results)
        results.find do |result|
          certainity_level = analyse_explain(result)

          break certainity_level if certainity_level
        end
      end

      private

      # rubocop: disable Metrics/CyclomaticComplexity
      # rubocop: disable Metrics/PerceivedComplexity
      def analyse_explain(result)
        type = result.fetch("type")
        possible_keys = result.fetch("possible_keys")
        key = result.fetch("key")
        extra = result.fetch("Extra")

        # more details about the result in https://dev.mysql.com/doc/refman/8.0/en/explain-output.html
        return if type == "ref"
        return if ALLOWED_EXTRA_VALUES.any? { |value| extra&.include?(value) }

        return :certain if possible_keys.nil?
        return :uncertain if possible_keys == "PRIMARY" && key.nil? && type == "ALL"
      end
      # rubocop: enable Metrics/CyclomaticComplexity
      # rubocop: enable Metrics/PerceivedComplexity
    end
  end
end

Version data entries

2 entries across 2 versions & 1 rubygems

Version	Path
wt_activerecord_index_spy-0.4.1	lib/wt_activerecord_index_spy/query_analyser/mysql.rb
wt_activerecord_index_spy-0.4.0	lib/wt_activerecord_index_spy/query_analyser/mysql.rb