MySQL 工具使用笔记

1. 索引
- 1.1. explain 工具
- 1.2. 使用 optimize trace 工具

1. 索引

1.1. explain 工具

直接通过在 query 的前面添加 explain 关键字就可以得到查询计划

explain select * from t;

id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	t	NULL	ALL	NULL	NULL	NULL	NULL	6	100.00	NULL

1.2. 使用 optimize trace 工具

开启 optimize trace 工具，先开启配置项，结果在 information_schema.optimizer_trace 查看结果

{
  "steps": [
    {
      "join_preparation": {
        "select#": 1,
        "steps": [
          {
            "expanded_query": "/* select#1 */ select count(0) AS `count(*)` from `t`"
          }
        ]
      }
    },
    {
      "join_optimization": {
        "select#": 1,
        "steps": [
          {
            "table_dependencies": [
              {
                "table": "`t`",
                "row_may_be_null": false,
                "map_bit": 0,
                "depends_on_map_bits": [
                ]
              }
            ]
          },
          {
            "rows_estimation": [
              {
                "table": "`t`",
                "table_scan": {
                  "rows": 6,
                  "cost": 0.25
                }
              }
            ]
          },
          {
            "considered_execution_plans": [
              {
                "plan_prefix": [
                ],
                "table": "`t`",
                "best_access_path": {
                  "considered_access_paths": [
                    {
                      "rows_to_scan": 6,
                      "access_type": "scan",
                      "resulting_rows": 6,
                      "cost": 0.85,
                      "chosen": true
                    }
                  ]
                },
                "condition_filtering_pct": 100,
                "rows_for_plan": 6,
                "cost_for_plan": 0.85,
                "chosen": true
              }
            ]
          },
          {
            "attaching_conditions_to_tables": {
              "original_condition": null,
              "attached_conditions_computation": [
              ],
              "attached_conditions_summary": [
                {
                  "table": "`t`",
                  "attached": null
                }
              ]
            }
          },
          {
            "optimizing_distinct_group_by_order_by": {
            }
          },
          {
            "finalizing_table_conditions": [
            ]
          },
          {
            "refine_plan": [
              {
                "table": "`t`"
              }
            ]
          },
          {
            "considering_tmp_tables": [
            ]
          }
        ]
      }
    },
    {
      "join_execution": {
        "select#": 1,
        "steps": [
        ]
      }
    }
  ]
}

MySQL 工具使用笔记

Table of Contents

1. 索引

1.1. explain 工具

1.2. 使用 optimize trace 工具