Optimize Trace

介绍

Optimizer Trace 是 MySQL 5.6.3 里新加的一个特性，可以把 MySQL Optimizer 的决策和执行过程输出成文本。输出使用 JSON 格式，便于程序分析和人类阅读。

使用方法

因为 Optimizer Trace 默认是关闭状态，先启用它。

SET optimizer_trace="enabled=on";

同时执行计划和 select trace 语句：

EXPLAIN SELECT create_time FROM tb_openemptycard_order WHERE create_time > UNIX_TIMESTAMP('2018-08-08')*1000;
select trace from information_schema.optimizer_trace;

输出中则会显示 trace 文本，以 json 的格式展示。

执行结果

{
  "steps": [
    {
      "join_preparation": {
        "select#": 1,
        "steps": [
          {
            "expanded_query": "/* select#1 */ select `tb_openemptycard_order`.`create_time` AS `create_time` from `tb_openemptycard_order` where (`tb_openemptycard_order`.`create_time` > 1533657600000)"
          }
        ]
      }
    },
    {
      "join_optimization": {
        "select#": 1,
        "steps": [
          {
            "condition_processing": {
              "condition": "WHERE",
              "original_condition": "(`tb_openemptycard_order`.`create_time` > 1533657600000)",
              "steps": [
                {
                  "transformation": "equality_propagation",
                  "resulting_condition": "(`tb_openemptycard_order`.`create_time` > 1533657600000)"
                },
                {
                  "transformation": "constant_propagation",
                  "resulting_condition": "(`tb_openemptycard_order`.`create_time` > 1533657600000)"
                },
                {
                  "transformation": "trivial_condition_removal",
                  "resulting_condition": "(`tb_openemptycard_order`.`create_time` > 1533657600000)"
                }
              ]
            }
          },
          {
            "substitute_generated_columns": {}
          },
          {
            "table_dependencies": [
              {
                "table": "`tb_openemptycard_order`",
                "row_may_be_null": false,
                "map_bit": 0,
                "depends_on_map_bits": []
              }
            ]
          },
          {
            "ref_optimizer_key_uses": []
          },
          {
            "rows_estimation": [
              {
                "table": "`tb_openemptycard_order`",
                "range_analysis": {
                  "table_scan": {
                    "rows": 538619,
                    "cost": 213454
                  },
                  "potential_range_indexes": [
                    {
                      "index": "PRIMARY",
                      "usable": false,
                      "cause": "not_applicable"
                    },
                    {
                      "index": "sys_order_id",
                      "usable": false,
                      "cause": "not_applicable"
                    },
                    {
                      "index": "user_id",
                      "usable": false,
                      "cause": "not_applicable"
                    },
                    {
                      "index": "iccid",
                      "usable": false,
                      "cause": "not_applicable"
                    },
                    {
                      "index": "dealer_id",
                      "usable": false,
                      "cause": "not_applicable"
                    },
                    {
                      "index": "sys_order_id_pay",
                      "usable": false,
                      "cause": "not_applicable"
                    },
                    {
                      "index": "transaction_id",
                      "usable": false,
                      "cause": "not_applicable"
                    },
                    {
                      "index": "app_type",
                      "usable": false,
                      "cause": "not_applicable"
                    },
                    {
                      "index": "create_time",
                      "usable": true,
                      "key_parts": [
                        "create_time",
                        "id"
                      ]
                    },
                    {
                      "index": "order_status",
                      "usable": false,
                      "cause": "not_applicable"
                    },
                    {
                      "index": "modify_time",
                      "usable": false,
                      "cause": "not_applicable"
                    },
                    {
                      "index": "phone_number",
                      "usable": false,
                      "cause": "not_applicable"
                    }
                  ],
                  "best_covering_index_scan": {
                    "index": "create_time",
                    "cost": 108578,
                    "chosen": true
                  },
                  "setup_range_conditions": [],
                  "group_index_range": {
                    "chosen": false,
                    "cause": "not_group_by_or_distinct"
                  },
                  "analyzing_range_alternatives": {
                    "range_scan_alternatives": [
                      {
                        "index": "create_time",
                        "ranges": [
                          "1533657600000 < create_time"
                        ],
                        "index_dives_for_eq_ranges": true,
                        "rowid_ordered": false,
                        "using_mrr": false,
                        "index_only": true,
                        "rows": 269309,
                        "cost": 54290,
                        "chosen": true
                      }
                    ],
                    "analyzing_roworder_intersect": {
                      "usable": false,
                      "cause": "too_few_roworder_scans"
                    }
                  },
                  "chosen_range_access_summary": {
                    "range_access_plan": {
                      "type": "range_scan",
                      "index": "create_time",
                      "rows": 269309,
                      "ranges": [
                        "1533657600000 < create_time"
                      ]
                    },
                    "rows_for_plan": 269309,
                    "cost_for_plan": 54290,
                    "chosen": true
                  }
                }
              }
            ]
          },
          {
            "considered_execution_plans": [
              {
                "plan_prefix": [],
                "table": "`tb_openemptycard_order`",
                "best_access_path": {
                  "considered_access_paths": [
                    {
                      "rows_to_scan": 269309,
                      "access_type": "range",
                      "range_details": {
                        "used_index": "create_time"
                      },
                      "resulting_rows": 269309,
                      "cost": 108151,
                      "chosen": true
                    }
                  ]
                },
                "condition_filtering_pct": 100,
                "rows_for_plan": 269309,
                "cost_for_plan": 108151,
                "chosen": true
              }
            ]
          },
          {
            "attaching_conditions_to_tables": {
              "original_condition": "(`tb_openemptycard_order`.`create_time` > 1533657600000)",
              "attached_conditions_computation": [],
              "attached_conditions_summary": [
                {
                  "table": "`tb_openemptycard_order`",
                  "attached": "(`tb_openemptycard_order`.`create_time` > 1533657600000)"
                }
              ]
            }
          },
          {
            "refine_plan": [
              {
                "table": "`tb_openemptycard_order`"
              }
            ]
          }
        ]
      }
    },
    {
      "join_explain": {
        "select#": 1,
        "steps": []
      }
    }
  ]
}

很多时候我们只看 considered_execution_plans 内容，然后分析执行计划得出的结论。