MySQL（十五）分析优化器的查询计划：Trace

合集 - MySQL高级(30)

1.MySQL（一）Linux下MySQL的安装2023-02-162.MySQL（二）字符集、比较规则与规范2023-02-163.MySQL（三）数据目录2023-02-164.MySQL（四）用户与权限管理2023-02-165.MySQL（五）配置文件、系统变量与MySQL架构2023-03-176.MySQL（六）存储引擎2023-03-177.MySQL（七）索引2023-03-178.MySQL（八）哈希索引、AVL树、B树与B+树的比较2023-03-179.MySQL（九）InnoDB行格式2023-04-0310.MySQL（九）InnoDB数据结构2023-04-0311.MySQL（十）表空间结构：区、段与碎片区2023-04-0312.MySQL（十一）索引的分类和创建原则2023-04-0513.MySQL（十二）索引使用的情况分析2023-04-0614.MySQL（十三）MySQL性能分析工具：慢查询日志与PROFILE查询成本2023-04-0715.MySQL（十四）分析查询语句Explain 七千字总结2023-04-14

16.MySQL（十五）分析优化器的查询计划：Trace2023-07-18

17.MySQL（十六）索引优化：索引失效的情况分析2023-04-2918.MySQL（十七）查询优化（一）2023-05-0219.MySQL（十七）查询优化（二）与数据库主键设计2023-05-0220.MySQL（十八）MySQL事务(一)：事务的概述与使用2023-05-0421.MySQL（十八）MySQL事务(二)：事务的隔离级别2023-05-0922.MySQL（十九）MySQL事务日志（一）RedoLog2023-05-0923.MySQL（十九）MySQL事务日志（二）UndoLog2023-05-0924.MySQL（二十）锁（一）锁的概述与S、X锁2023-05-0925.MySQL（二十）锁（二）表锁、行锁与页级锁2023-05-0926.MySQL（二十）锁（三）乐观锁与悲观锁、显示隐式锁和其他锁2023-05-0927.MySQL（二十一）MVCC多版本并发控制2023-07-1828.MySQL（二十二）其他数据库日志（一）通用查询日志和错误日志2023-05-0929.MySQL（二十二）其他数据库日志（二）bin log二进制日志与中继日志2023-05-0930.【完结撒花】MySQL（二十三）主从复制2023-05-10

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1 MySQL（十五）分析优化器的查询计划：Trace

---

​ OPTIMIZER_TRACE是mysql 5.6引入的一项追踪功能，它可以追踪优化器做出的各种决策（比如访问表的方法、各种开销计算和各种转换等等），并将结果记录到表INFORMATION_SCHEMA.OPTIMIZER_TRACE表中。

​ Trace功能默认是关闭的，需要开启trace，设置JSON格式，并设置最大能使用内存为1000000，防止使用过程中因内存过小而不能够使用

SET optimizer_trace = 'enabled=on', end_markers_in_json=on;
set optimizer_trace_max_mem_size=1000000;

​ 测试 并查看对应计划

SELECT * FROM student WHERE id < 2042366;

mysql> SELECT * FROM information_schema.OPTIMIZER_TRACE\G;
*************************** 1. row ***************************
# 第一部分：查询的SQL
QUERY: SELECT * FROM student WHERE id < 2042366
# 第二部分：追踪的信息
TRACE: {
  "steps": [
    {
      "join_preparation": {
        "select#": 1,
        "steps": [
          {
            "expanded_query": "/* select#1 */ select `student`.`id` AS `id`,`student`.`stuno` AS `stuno`,`student`.`name` AS `name`,`student`.`age` AS `age`,`student`.`classid` AS `classid` from `student` where (`student`.`id` < 2042366)"
          }
        ] /* steps */
      } /* join_preparation */
    },
    {
      "join_optimization": {
        "select#": 1,
        "steps": [
          {
            "condition_processing": {
              "condition": "WHERE",
              "original_condition": "(`student`.`id` < 2042366)",
              "steps": [
                {
                  "transformation": "equality_propagation",
                  "resulting_condition": "(`student`.`id` < 2042366)"
                },
                {
                  "transformation": "constant_propagation",
                  "resulting_condition": "(`student`.`id` < 2042366)"
                },
                {
                  "transformation": "trivial_condition_removal",
                  "resulting_condition": "(`student`.`id` < 2042366)"
                }
              ] /* steps */
            } /* condition_processing */
          },
          {
            "substitute_generated_columns": {
            } /* substitute_generated_columns */
          },
          {
            "table_dependencies": [
              {
                "table": "`student`",
                "row_may_be_null": false,
                "map_bit": 0,
                "depends_on_map_bits": [
                ] /* depends_on_map_bits */
              }
            ] /* table_dependencies */
          },
          {
            "ref_optimizer_key_uses": [
            ] /* ref_optimizer_key_uses */
          },
          {
            "rows_estimation": [
              {
                "table": "`student`",
                "range_analysis": {
                  "table_scan": {
                    "rows": 3989929,
                    "cost": 406388
                  } /* table_scan */,
                  "potential_range_indexes": [
                    {
                      "index": "PRIMARY",
                      "usable": true,
                      "key_parts": [
                        "id"
                      ] /* key_parts */
                    }
                  ] /* potential_range_indexes */,
                  "setup_range_conditions": [
                  ] /* setup_range_conditions */,
                  "group_index_range": {
                    "chosen": false,
                    "cause": "not_group_by_or_distinct"
                  } /* group_index_range */,
                  "skip_scan_range": {
                    "potential_skip_scan_indexes": [
                      {
                        "index": "PRIMARY",
                        "usable": false,
                        "cause": "query_references_nonkey_column"
                      }
                    ] /* potential_skip_scan_indexes */
                  } /* skip_scan_range */,
                  "analyzing_range_alternatives": {
                    "range_scan_alternatives": [
                      {
                        "index": "PRIMARY",
                        "ranges": [
                          "id < 2042366"
                        ] /* ranges */,
                        "index_dives_for_eq_ranges": true,
                        "rowid_ordered": true,
                        "using_mrr": false,
                        "index_only": false,
                        "in_memory": 0.386539,
                        "rows": 19,
                        "cost": 2.635,
                        "chosen": true
                      }
                    ] /* range_scan_alternatives */,
                    "analyzing_roworder_intersect": {
                      "usable": false,
                      "cause": "too_few_roworder_scans"
                    } /* analyzing_roworder_intersect */
                  } /* analyzing_range_alternatives */,
                  "chosen_range_access_summary": {
                    "range_access_plan": {
                      "type": "range_scan",
                      "index": "PRIMARY",
                      "rows": 19,
                      "ranges": [
                        "id < 2042366"
                      ] /* ranges */
                    } /* range_access_plan */,
                    "rows_for_plan": 19,
                    "cost_for_plan": 2.635,
                    "chosen": true
                  } /* chosen_range_access_summary */
                } /* range_analysis */
              }
            ] /* rows_estimation */
          },
          {
            "considered_execution_plans": [
              {
                "plan_prefix": [
                ] /* plan_prefix */,
                "table": "`student`",
                "best_access_path": {
                  "considered_access_paths": [
                    {
                      "rows_to_scan": 19,
                      "access_type": "range",
                      "range_details": {
                        "used_index": "PRIMARY"
                      } /* range_details */,
                      "resulting_rows": 19,
                      "cost": 4.535,
                      "chosen": true
                    }
                  ] /* considered_access_paths */
                } /* best_access_path */,
                "condition_filtering_pct": 100,
                "rows_for_plan": 19,
                "cost_for_plan": 4.535,
                "chosen": true
              }
            ] /* considered_execution_plans */
          },
          {
            "attaching_conditions_to_tables": {
              "original_condition": "(`student`.`id` < 2042366)",
              "attached_conditions_computation": [
              ] /* attached_conditions_computation */,
              "attached_conditions_summary": [
                {
                  "table": "`student`",
                  "attached": "(`student`.`id` < 2042366)"
                }
              ] /* attached_conditions_summary */
            } /* attaching_conditions_to_tables */
          },
          {
            "finalizing_table_conditions": [
              {
                "table": "`student`",
                "original_table_condition": "(`student`.`id` < 2042366)",
                "final_table_condition   ": "(`student`.`id` < 2042366)"
              }
            ] /* finalizing_table_conditions */
          },
          {
            "refine_plan": [
              {
                "table": "`student`"
              }
            ] /* refine_plan */
          }
        ] /* steps */
      } /* join_optimization */
    },
    {
      "join_execution": {
        "select#": 1,
        "steps": [
        ] /* steps */
      } /* join_execution */
    }
  ] /* steps */
}
# 第三部分：追踪信息过长导致被截断的字节数
MISSING_BYTES_BEYOND_MAX_MEM_SIZE: 0
          INSUFFICIENT_PRIVILEGES: 0
1 row in set (0.00 sec)
 

2 mysql监控分析视图-sys schema

---

索引情况

-- 查询冗余索引
SELECT * FROM sys.schema_redundant_indexes;
-- 查询未使用过的索引 
SELECT * FROM sys.schema_unused_indexes;
-- 查询索引的使用情况
SELECT index_name, rows_selected, rows_inserted, rows_updated, rows_deleted
FROM sys.schema_index_statistics
WHERE table_schema = 'atguigudb1'

表情况

-- 查询表的访问量
SELECT table_schema, table_name, SUM(io_read_requests + io_write_requests) AS io
FROM sys.schema_table_statistics GROUP BY table_schema, table_name ORDER BY io;
-- 查询占用 buffer pool较多的表
SELECT object_schema, object_name, allocated, DATA
FROM sys.innodb_buffer_stats_by_table ORDER BY allocated LIMIT 10；
-- 查看表的全表扫描情况
SELECT * FROM sys.statements_with_full_table_scans WHERE db='atguigudb1'

语句相关

-- 监控SQL执行的频率
SELECT db, exec_count, query from sys.statement_analysis
ORDER BY exec_count DESC
 
-- 监控使用了排序的SQL
SELECT db, exec_count, first_seen, last_seen, query
FROM sys.statements_with_sorting limit 1
 
-- 监控使用了临时表或者磁盘临时表的SQL
SELECT db, exec_count, tmp_tables, tmp_disk_tables, query 
from sys.statement_analysis 
WHERE tmp_tables > 0 or tmp_disk_tables > 0
ORDER BY (tmp_tables + tmp_disk_tables) DESC

注意

通过sys库去查询的时候，mysql会耗费大量的资源去收集信息，严重的情况可能会导致业务请求被阻塞，从而引起故障，生产的时候尽量不要去频繁查看sys或者performance_schema、information_schema来完成监控、巡检等工作