数据库
首页 > 数据库> > 数据库调优-02

数据库调优-02

作者:互联网

目录

三、SQL分析

2、OPTIMIZER_TRACE 详解

OPTIMIZER_TRACE是 MySQL 5.6引入的一项跟踪功能,它可以跟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、各种转换等),并将跟踪结果记录到 INFORMATION_SCHEMA.OPTIMIZER_TRACE 表中。此功能默认关闭,开启后,可分析如下语句:SELECT、INSERT、REPLACE、UPDATE、DELETE、EXPLAIN、SET、DECLARE、CASE、IF、RETURN、CALL。

2.1 OPTIMIZER_TRACE 相关参数

参考 https://dev.mysql.com/doc/internals/en/system-variables-controlling-trace.html

-- 以上参数可用SET语句操作,例如,用如下命令即可打开OPTIMIZER TRACE
SET OPTIMIZER_TRACE="enabled=on",END_MARKERS_IN_JSON=on;

-- 也可用SET GLOBAL全局开启。但即使全局开启OPTIMIZER_TRACE,每个Session也只能跟踪它自己执行的语句:
SET GLOBAL OPTIMIZER_TRACE="enabled=on",END_MARKERS_IN_JSON=on;

optimizer_trace_limit和optimizer_trace_offset这两个参数经常配合使用,例如:

SET optimizer_trace_offset=<OFFSET>, optimizer_trace_limit=<LIMIT>

这两个参数配合使用,有点类似MySQL里面的 limit语句。
默认情况下,由于optimizer_trace_offset=-1,optimizer_trace_limit=1,记录最近的一条SQL语句,展示时,每次展示1条数据;

如果改成 SET optimizer_trace_offset=-2, optimizer_trace_limit=1,则会记录倒数第二条SQL语句;

有关 optimizer_trace_offset 、optimizer_trace_limit更多细节,可参考 https://dev.mysql.com/doc/internals/en/tuning-trace-purging.html

2.2 OPTIMIZER_TRACE 使用

1、开启OPTIMIZER_TRACE功能,并设置要展示的数据条目数:

SET OPTIMIZER_TRACE="enabled=on",END_MARKERS_IN_JSON=on;
SET optimizer_trace_offset=-30, optimizer_trace_limit=30;

2、发送你想要分析的SQL语句,例如:

select * from salaries where from_date = '1986-06-26' and to_date = '1987-06-26';

3、使用如下语句分析,即可获得类似如下的结果:

mysql> SELECT * FROM INFORMATION_SCHEMA.OPTIMIZER_TRACE limit 30 \G;
*************************** 1. row ***************************
                          QUERY: select *
from salaries
where from_date = '1986-06-26'
  and to_date = '1987-06-26'
                            TRACE: {
  "steps": [
    {
      "join_preparation": {
        "select#": 1,
        "steps": [
          {
            "expanded_query": "/* select#1 */ select `salaries`.`emp_no` AS `emp_no`,`salaries`.`salary` AS `salary`,`salaries`.`from_date` AS `from_date`,`salaries`.`to_date` AS `to_date` from `salaries` where ((`salaries`.`from_date` = '1986-06-26') and (`salaries`.`to_date` = '1987-06-26'))"
          }
        ] /* steps */
      } /* join_preparation */
    },
    {
      "join_optimization": {
        "select#": 1,
        "steps": [
          {
            "condition_processing": {
              "condition": "WHERE",
              "original_condition": "((`salaries`.`from_date` = '1986-06-26') and (`salaries`.`to_date` = '1987-06-26'))",
              "steps": [
                {
                  "transformation": "equality_propagation",
                  "resulting_condition": "(multiple equal('1986-06-26', `salaries`.`from_date`) and multiple equal('1987-06-26', `salaries`.`to_date`))"
                },
                {
                  "transformation": "constant_propagation",
                  "resulting_condition": "(multiple equal('1986-06-26', `salaries`.`from_date`) and multiple equal('1987-06-26', `salaries`.`to_date`))"
                },
                {
                  "transformation": "trivial_condition_removal",
                  "resulting_condition": "(multiple equal(DATE'1986-06-26', `salaries`.`from_date`) and multiple equal(DATE'1987-06-26', `salaries`.`to_date`))"
                }
              ] /* steps */
            } /* condition_processing */
          },
          {
            "substitute_generated_columns": {
            } /* substitute_generated_columns */
          },
          {
            "table_dependencies": [
              {
                "table": "`salaries`",
                "row_may_be_null": false,
                "map_bit": 0,
                "depends_on_map_bits": [
                ] /* depends_on_map_bits */
              }
            ] /* table_dependencies */
          },
          {
            "ref_optimizer_key_uses": [
              {
                "table": "`salaries`",
                "field": "from_date",
                "equals": "DATE'1986-06-26'",
                "null_rejecting": false
              },
              {
                "table": "`salaries`",
                "field": "to_date",
                "equals": "DATE'1987-06-26'",
                "null_rejecting": false
              }
            ] /* ref_optimizer_key_uses */
          },
          {
            "rows_estimation": [
              {
                "table": "`salaries`",
                "range_analysis": {
                  "table_scan": {
                    "rows": 2838216,
                    "cost": 286799
                  } /* table_scan */,
                  "potential_range_indexes": [
                    {
                      "index": "PRIMARY",
                      "usable": false,
                      "cause": "not_applicable"
                    },
                    {
                      "index": "salaries_from_date_to_date_index",
                      "usable": true,
                      "key_parts": [
                        "from_date",
                        "to_date",
                        "emp_no"
                      ] /* 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": "salaries_from_date_to_date_index",
                        "usable": false,
                        "cause": "query_references_nonkey_column"
                      }
                    ] /* potential_skip_scan_indexes */
                  } /* skip_scan_range */,
                  "analyzing_range_alternatives": {
                    "range_scan_alternatives": [
                      {
                        "index": "salaries_from_date_to_date_index",
                        "ranges": [
                          "0xda840f <= from_date <= 0xda840f AND 0xda860f <= to_date <= 0xda860f"
                        ] /* ranges */,
                        "index_dives_for_eq_ranges": true,
                        "rowid_ordered": true,
                        "using_mrr": false,
                        "index_only": false,
                        "rows": 86,
                        "cost": 50.909,
                        "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": "salaries_from_date_to_date_index",
                      "rows": 86,
                      "ranges": [
                        "0xda840f <= from_date <= 0xda840f AND 0xda860f <= to_date <= 0xda860f"
                      ] /* ranges */
                    } /* range_access_plan */,
                    "rows_for_plan": 86,
                    "cost_for_plan": 50.909,
                    "chosen": true
                  } /* chosen_range_access_summary */
                } /* range_analysis */
              }
            ] /* rows_estimation */
          },
          {
            "considered_execution_plans": [
              {
                "plan_prefix": [
                ] /* plan_prefix */,
                "table": "`salaries`",
                "best_access_path": {
                  "considered_access_paths": [
                    {
                      "access_type": "ref",
                      "index": "salaries_from_date_to_date_index",
                      "rows": 86,
                      "cost": 50.412,
                      "chosen": true
                    },
                    {
                      "access_type": "range",
                      "range_details": {
                        "used_index": "salaries_from_date_to_date_index"
                      } /* range_details */,
                      "chosen": false,
                      "cause": "heuristic_index_cheaper"
                    }
                  ] /* considered_access_paths */
                } /* best_access_path */,
                "condition_filtering_pct": 100,
                "rows_for_plan": 86,
                "cost_for_plan": 50.412,
                "chosen": true
              }
            ] /* considered_execution_plans */
          },
          {
            "attaching_conditions_to_tables": {
              "original_condition": "((`salaries`.`to_date` = DATE'1987-06-26') and (`salaries`.`from_date` = DATE'1986-06-26'))",
              "attached_conditions_computation": [
              ] /* attached_conditions_computation */,
              "attached_conditions_summary": [
                {
                  "table": "`salaries`",
                  "attached": "((`salaries`.`to_date` = DATE'1987-06-26') and (`salaries`.`from_date` = DATE'1986-06-26'))"
                }
              ] /* attached_conditions_summary */
            } /* attaching_conditions_to_tables */
          },
          {
            "finalizing_table_conditions": [
              {
                "table": "`salaries`",
                "original_table_condition": "((`salaries`.`to_date` = DATE'1987-06-26') and (`salaries`.`from_date` = DATE'1986-06-26'))",
                "final_table_condition   ": null
              }
            ] /* finalizing_table_conditions */
          },
          {
            "refine_plan": [
              {
                "table": "`salaries`"
              }
            ] /* refine_plan */
          }
        ] /* steps */
      } /* join_optimization */
    },
    {
      "join_execution": {
        "select#": 1,
        "steps": [
        ] /* steps */
      } /* join_execution */
    }
  ] /* steps */
}
MISSING_BYTES_BEYOND_MAX_MEM_SIZE: 0
          INSUFFICIENT_PRIVILEGES: 0
1 row in set (0.00 sec)

4、分析完成,关闭OPTIMIZER_TRACE

SET optimizer_trace="enabled=off";

2.3 OPTIMIZER_TRACE 结果分析

由上面的结果可知,OPTIMIZER_TRACE有四个字段:

最核心的是TRACE字段的内容。我们逐段分析:

join_preparation

join_preparation段落展示了准备阶段的执行过程。

{
  "join_preparation": {
    "select#": 1,
    "steps": [
      {
        -- 对比下原始语句,可以知道,这一步做了个格式化。
        "expanded_query": "/* select#1 */ select `salaries`.`emp_no` AS `emp_no`,`salaries`.`salary` AS `salary`,`salaries`.`from_date` AS `from_date`,`salaries`.`to_date` AS `to_date` from `salaries` where ((`salaries`.`from_date` = '1986-06-26') and (`salaries`.`to_date` = '1987-06-26'))"
      }
    ]
    /* steps */
  }
  /* join_preparation */
}
join_optimization

join_optimization展示了优化阶段的执行过程,是分析OPTIMIZER TRACE的重点。这段内容超级长,而且分了好多步骤,不妨按照步骤逐段分析:

condition_processing
该段用来做条件处理,主要对WHERE条件进行优化处理。

"condition_processing": {
  "condition": "WHERE",
  "original_condition": "((`salaries`.`from_date` = '1986-06-26') and (`salaries`.`to_date` = '1987-06-26'))",
  "steps": [
    {
      "transformation": "equality_propagation",
      "resulting_condition": "(multiple equal('1986-06-26', `salaries`.`from_date`) and multiple equal('1987-06-26', `salaries`.`to_date`))"
    },
    {
      "transformation": "constant_propagation",
      "resulting_condition": "(multiple equal('1986-06-26', `salaries`.`from_date`) and multiple equal('1987-06-26', `salaries`.`to_date`))"
    },
    {
      "transformation": "trivial_condition_removal",
      "resulting_condition": "(multiple equal(DATE'1986-06-26', `salaries`.`from_date`) and multiple equal(DATE'1987-06-26', `salaries`.`to_date`))"
    }
  ] /* steps */
} /* condition_processing */

其中:

substitute_generated_columns
substitute_generated_columns用于替换虚拟生成列

"substitute_generated_columns": {
} /* substitute_generated_columns */

table_dependencies
分析表之间的依赖关系

{
  "table_dependencies": [
    {
      "table": "`salaries`",
      "row_may_be_null": false,
      "map_bit": 0,
      "depends_on_map_bits": [
      ] /* depends_on_map_bits */
    }
  ] /* table_dependencies */
}

其中:

ref_optimizer_key_uses
列出所有可用的ref类型的索引。如果使用了组合索引的多个部分(例如本例,用到了index(from_date, to_date) 的多列索引),则会在ref_optimizer_key_uses下列出多个元素,每个元素中会列出ref使用的索引及对应值。

{
  "ref_optimizer_key_uses": [
    {
      "table": "`salaries`",
      "field": "from_date",
      "equals": "DATE'1986-06-26'",
      "null_rejecting": false
    },
    {
      "table": "`salaries`",
      "field": "to_date",
      "equals": "DATE'1987-06-26'",
      "null_rejecting": false
    }
  ] /* ref_optimizer_key_uses */
}

rows_estimation
顾名思义,用于估算需要扫描的记录数。

{
  "rows_estimation": [
    {
      "table": "`salaries`",
      "range_analysis": {
        "table_scan": {
          "rows": 2838216,
          "cost": 286799
        } /* table_scan */,
        "potential_range_indexes": [
          {
            "index": "PRIMARY",
            "usable": false,
            "cause": "not_applicable"
          },
          {
            "index": "salaries_from_date_to_date_index",
            "usable": true,
            "key_parts": [
              "from_date",
              "to_date",
              "emp_no"
            ] /* 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": "salaries_from_date_to_date_index",
              "usable": false,
              "cause": "query_references_nonkey_column"
            }
          ] /* potential_skip_scan_indexes */
        } /* skip_scan_range */,
        "analyzing_range_alternatives": {
          "range_scan_alternatives": [
            {
              "index": "salaries_from_date_to_date_index",
              "ranges": [
                "0xda840f <= from_date <= 0xda840f AND 0xda860f <= to_date <= 0xda860f"
              ] /* ranges */,
              "index_dives_for_eq_ranges": true,
              "rowid_ordered": true,
              "using_mrr": false,
              "index_only": false,
              "rows": 86,
              "cost": 50.909,
              "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": "salaries_from_date_to_date_index",
            "rows": 86,
            "ranges": [
              "0xda840f <= from_date <= 0xda840f AND 0xda860f <= to_date <= 0xda860f"
            ] /* ranges */
          } /* range_access_plan */,
          "rows_for_plan": 86,
          "cost_for_plan": 50.909,
          "chosen": true
        } /* chosen_range_access_summary */
      } /* range_analysis */
    }
  ] /* rows_estimation */
}

其中:

considered_execution_plans
负责对比各可行计划的开销,并选择相对最优的执行计划。

{
  "considered_execution_plans": [
    {
      "plan_prefix": [
      ] /* plan_prefix */,
      "table": "`salaries`",
      "best_access_path": {
        "considered_access_paths": [
          {
            "access_type": "ref",
            "index": "salaries_from_date_to_date_index",
            "rows": 86,
            "cost": 50.412,
            "chosen": true
          },
          {
            "access_type": "range",
            "range_details": {
              "used_index": "salaries_from_date_to_date_index"
            } /* range_details */,
            "chosen": false,
            "cause": "heuristic_index_cheaper"
          }
        ] /* considered_access_paths */
      } /* best_access_path */,
      "condition_filtering_pct": 100,
      "rows_for_plan": 86,
      "cost_for_plan": 50.412,
      "chosen": true
    }
  ] /* considered_execution_plans */
}

其中:

attaching_conditions_to_tables
基于considered_execution_plans中选择的执行计划,改造原有where条件,并针对表增加适当的附加条件,以便于单表数据的筛选。

TIPS

{
  "attaching_conditions_to_tables": {
    "original_condition": "((`salaries`.`to_date` = DATE'1987-06-26') and (`salaries`.`from_date` = DATE'1986-06-26'))",
    "attached_conditions_computation": [
    ] /* attached_conditions_computation */,
    "attached_conditions_summary": [
      {
        "table": "`salaries`",
        "attached": "((`salaries`.`to_date` = DATE'1987-06-26') and (`salaries`.`from_date` = DATE'1986-06-26'))"
      }
    ] /* attached_conditions_summary */
  } /* attaching_conditions_to_tables */
}

其中:

finalizing_table_conditions
最终的、经过优化后的表条件。

{
  "finalizing_table_conditions": [
    {
      "table": "`salaries`",
      "original_table_condition": "((`salaries`.`to_date` = DATE'1987-06-26') and (`salaries`.`from_date` = DATE'1986-06-26'))",
      "final_table_condition   ": null
    }
  ] /* finalizing_table_conditions */
}

refine_plan
改善执行计划:

{
  "refine_plan": [
    {
      "table": "`salaries`"
    }
  ] /* refine_plan */
}

其中:

join_execution

join_execution段落展示了执行阶段的执行过程。

"join_execution": {
  "select#": 1,
  "steps": [
  ] /* steps */
}
参考文档

Tracing the Optimizer
手把手教你认识OPTIMIZER_TRACE
MYSQL sql执行过程的一些跟踪分析(二.mysql优化器追踪分析)
使用 Trace 进行执行计划分析

标签:02,index,26,06,数据库,salaries,range,调优,date
来源: https://www.cnblogs.com/jinshengnianhua/p/15362374.html