Full MySQL optimizer trace for "How to capture supporting information with your SQL statements"

optimizer-trace.json

{
  "steps": [
    {
      "join_preparation": {
        "select#": 1,
        "steps": [
          {
            "expanded_query": "/* select#1 */ select `a`.`country_code` AS `country_code`,`c`.`name` AS `name`,count(0) AS `cnt` from (`airport` `a` join `country` `c` on((`a`.`country_code` = `c`.`country_code`))) group by `a`.`country_code`,`c`.`name` order by count(0) desc limit 10"
          },
          {
            "transformations_to_nested_joins": {
              "transformations": [
                "JOIN_condition_to_WHERE",
                "parenthesis_removal"
              ],
              "expanded_query": "/* select#1 */ select `a`.`country_code` AS `country_code`,`c`.`name` AS `name`,count(0) AS `cnt` from `airport` `a` join `country` `c` where (`a`.`country_code` = `c`.`country_code`) group by `a`.`country_code`,`c`.`name` order by count(0) desc limit 10"
            }
          }
        ]
      }
    },
    {
      "join_optimization": {
        "select#": 1,
        "steps": [
          {
            "condition_processing": {
              "condition": "WHERE",
              "original_condition": "(`a`.`country_code` = `c`.`country_code`)",
              "steps": [
                {
                  "transformation": "equality_propagation",
                  "resulting_condition": "multiple equal(`a`.`country_code`, `c`.`country_code`)"
                },
                {
                  "transformation": "constant_propagation",
                  "resulting_condition": "multiple equal(`a`.`country_code`, `c`.`country_code`)"
                },
                {
                  "transformation": "trivial_condition_removal",
                  "resulting_condition": "multiple equal(`a`.`country_code`, `c`.`country_code`)"
                }
              ]
            }
          },
          {
            "substitute_generated_columns": {
            }
          },
          {
            "table_dependencies": [
              {
                "table": "`airport` `a`",
                "row_may_be_null": false,
                "map_bit": 0,
                "depends_on_map_bits": [
                ]
              },
              {
                "table": "`country` `c`",
                "row_may_be_null": false,
                "map_bit": 1,
                "depends_on_map_bits": [
                ]
              }
            ]
          },
          {
            "ref_optimizer_key_uses": [
              {
                "table": "`airport` `a`",
                "field": "country_code",
                "equals": "`c`.`country_code`",
                "null_rejecting": true
              },
              {
                "table": "`country` `c`",
                "field": "country_code",
                "equals": "`a`.`country_code`",
                "null_rejecting": true
              }
            ]
          },
          {
            "rows_estimation": [
              {
                "table": "`airport` `a`",
                "table_scan": {
                  "rows": 86733,
                  "cost": 296.25
                }
              },
              {
                "table": "`country` `c`",
                "table_scan": {
                  "rows": 248,
                  "cost": 1
                }
              }
            ]
          },
          {
            "considered_execution_plans": [
              {
                "plan_prefix": [
                ],
                "table": "`country` `c`",
                "best_access_path": {
                  "considered_access_paths": [
                    {
                      "access_type": "ref",
                      "index": "PRIMARY",
                      "usable": false,
                      "chosen": false
                    },
                    {
                      "rows_to_scan": 248,
                      "filtering_effect": [
                      ],
                      "final_filtering_effect": 1,
                      "access_type": "scan",
                      "resulting_rows": 248,
                      "cost": 25.8,
                      "chosen": true
                    }
                  ]
                },
                "condition_filtering_pct": 100,
                "rows_for_plan": 248,
                "cost_for_plan": 25.8,
                "rest_of_plan": [
                  {
                    "plan_prefix": [
                      "`country` `c`"
                    ],
                    "table": "`airport` `a`",
                    "best_access_path": {
                      "considered_access_paths": [
                        {
                          "access_type": "ref",
                          "index": "country_code",
                          "rows": 405.294,
                          "cost": 35179.6,
                          "chosen": true
                        },
                        {
                          "rows_to_scan": 86733,
                          "filtering_effect": [
                          ],
                          "final_filtering_effect": 1,
                          "access_type": "scan",
                          "using_join_cache": true,
                          "buffers_needed": 1,
                          "resulting_rows": 86733,
                          "cost": 2.15133e+06,
                          "chosen": false
                        }
                      ]
                    },
                    "condition_filtering_pct": 100,
                    "rows_for_plan": 100513,
                    "cost_for_plan": 35205.4,
                    "chosen": true
                  }
                ]
              },
              {
                "plan_prefix": [
                ],
                "table": "`airport` `a`",
                "best_access_path": {
                  "considered_access_paths": [
                    {
                      "access_type": "ref",
                      "index": "country_code",
                      "usable": false,
                      "chosen": false
                    },
                    {
                      "rows_to_scan": 86733,
                      "filtering_effect": [
                      ],
                      "final_filtering_effect": 1,
                      "access_type": "scan",
                      "resulting_rows": 86733,
                      "cost": 8969.55,
                      "chosen": true
                    }
                  ]
                },
                "condition_filtering_pct": 100,
                "rows_for_plan": 86733,
                "cost_for_plan": 8969.55,
                "rest_of_plan": [
                  {
                    "plan_prefix": [
                      "`airport` `a`"
                    ],
                    "table": "`country` `c`",
                    "best_access_path": {
                      "considered_access_paths": [
                        {
                          "access_type": "eq_ref",
                          "index": "PRIMARY",
                          "rows": 1,
                          "cost": 30356.6,
                          "chosen": true,
                          "cause": "clustered_pk_chosen_by_heuristics"
                        },
                        {
                          "rows_to_scan": 248,
                          "filtering_effect": [
                          ],
                          "final_filtering_effect": 1,
                          "access_type": "scan",
                          "using_join_cache": true,
                          "buffers_needed": 136,
                          "resulting_rows": 248,
                          "cost": 2.15112e+06,
                          "chosen": false
                        }
                      ]
                    },
                    "condition_filtering_pct": 100,
                    "rows_for_plan": 86733,
                    "cost_for_plan": 39326.1,
                    "pruned_by_cost": true
                  }
                ]
              }
            ]
          },
          {
            "attaching_conditions_to_tables": {
              "original_condition": "(`a`.`country_code` = `c`.`country_code`)",
              "attached_conditions_computation": [
              ],
              "attached_conditions_summary": [
                {
                  "table": "`country` `c`",
                  "attached": null
                },
                {
                  "table": "`airport` `a`",
                  "attached": "(`a`.`country_code` = `c`.`country_code`)"
                }
              ]
            }
          },
          {
            "optimizing_distinct_group_by_order_by": {
              "simplifying_order_by": {
                "original_clause": "count(0) desc",
                "items": [
                  {
                    "item": "count(0)"
                  }
                ],
                "resulting_clause_is_simple": false,
                "resulting_clause": "count(0) desc"
              },
              "simplifying_group_by": {
                "original_clause": "`a`.`country_code`,`c`.`name`",
                "items": [
                  {
                    "item": "`a`.`country_code`"
                  },
                  {
                    "item": "`c`.`name`"
                  }
                ],
                "resulting_clause_is_simple": false,
                "resulting_clause": "`a`.`country_code`,`c`.`name`"
              }
            }
          },
          {
            "finalizing_table_conditions": [
              {
                "table": "`airport` `a`",
                "original_table_condition": "(`a`.`country_code` = `c`.`country_code`)",
                "final_table_condition   ": null
              }
            ]
          },
          {
            "refine_plan": [
              {
                "table": "`country` `c`"
              },
              {
                "table": "`airport` `a`"
              }
            ]
          },
          {
            "considering_tmp_tables": [
              {
                "adding_tmp_table_in_plan_at_position": 2,
                "write_method": "continuously_update_group_row"
              },
              {
                "adding_sort_to_table": ""
              }
            ]
          }
        ]
      }
    },
    {
      "join_execution": {
        "select#": 1,
        "steps": [
          {
            "temp_table_aggregate": {
              "select#": 1,
              "steps": [
                {
                  "creating_tmp_table": {
                    "tmp_table_info": {
                      "in_plan_at_position": 2,
                      "columns": 3,
                      "row_length": 218,
                      "key_length": 210,
                      "unique_constraint": false,
                      "makes_grouped_rows": true,
                      "cannot_insert_duplicates": false,
                      "location": "TempTable"
                    }
                  }
                }
              ]
            }
          },
          {
            "sorting_table": "<temporary>",
            "filesort_information": [
              {
                "direction": "desc",
                "expression": "`cnt`"
              }
            ],
            "filesort_priority_queue_optimization": {
              "limit": 10,
              "chosen": true
            },
            "filesort_execution": [
            ],
            "filesort_summary": {
              "memory_available": 262144,
              "key_size": 8,
              "row_size": 226,
              "max_rows_per_buffer": 11,
              "num_rows_estimate": 18446744073709551615,
              "num_rows_found": 245,
              "num_initial_chunks_spilled_to_disk": 0,
              "peak_memory_used": 2574,
              "sort_algorithm": "std::sort",
              "unpacked_addon_fields": "using_priority_queue",
              "sort_mode": "<fixed_sort_key, additional_fields>"
            }
          }
        ]
      }
    }
  ]
}