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inner join执行计划变了
2022-06-11 21:43:00 【YoohuDeLi】
一、背景
同一个连接查询inner join，由于某一个条件in里多了几个值，执行计划变了。
执行计划一：
执行计划二：
二、外连接与内连接的区别
连接查询的成本计算公式是这样的：
连接查询总成本 = 单次访问驱动表的成本 + 驱动表扇出数 x 单次访问被驱动表的成本。
- 对于左（外）连接和右（外）连接查询来说，它们的驱动表是固定的，所以想要得到最优的查询方案只需要：分别为驱动表和被驱动表选择成本最低的访问方法。
- 对于内连接来说，驱动表和被驱动表的位置是可以互换的，所以需要考虑两个方面的问题：
（1）不同的表作为驱动表最终的查询成本可能是不同的，也就是需要考虑最优的表连接顺序。
（2）然后分别为驱动表和被驱动表选择成本最低的访问方法。
三、通过optimizer_trace查看决策过程
1、optimizer_trace的查看与开启
查看：show variables like ‘optimizer_trace’;
开启：set optimizer_trace=“enabled=on”;
2、optimizer_trace的使用
（1）打开optimizer trace功能（默认情况下它是关闭的）：
SET optimizer_trace=“enabled=on”;
（2）输入查询语句：
SELECT …;
（3）从OPTIMIZER_TRACE表中查看上一个查询的优化过程：
SELECT * FROM information_schema.OPTIMIZER_TRACE;
3、案例分析
（1）执行计划一的优化过程
{
"steps": [
{
"join_preparation": { # prepare阶段
"select#": 1,
"steps": [
{
"IN_uses_bisection": true
},
{
"expanded_query": "/* select#1 */ select distinct `q`.`question_id` AS `question_id` from (`tb_question` `q` join `tb_question_label` `label` on((`label`.`question_id` = `q`.`question_id`))) where ((`label`.`subject_id` = 11) and (`label`.`is_deleted` = 1) and (`label`.`label_id` in (197750,197637,197947)) and (`q`.`subject_id` = 11) and (`q`.`parent_id` = 0) and (`q`.`is_deleted` = 0) and (`q`.`quality` = 4)) limit 3000"
},
{
"transformations_to_nested_joins": {
"transformations": [
"JOIN_condition_to_WHERE",
"parenthesis_removal"
],
"expanded_query": "/* select#1 */ select distinct `q`.`question_id` AS `question_id` from `tb_question` `q` join `tb_question_label` `label` where ((`label`.`subject_id` = 11) and (`label`.`is_deleted` = 1) and (`label`.`label_id` in (197750,197637,197947)) and (`q`.`subject_id` = 11) and (`q`.`parent_id` = 0) and (`q`.`is_deleted` = 0) and (`q`.`quality` = 4) and (`label`.`question_id` = `q`.`question_id`)) limit 3000"
}
}
]
}
},
{
"join_optimization": { # optimize阶段
"select#": 1,
"steps": [
{
"condition_processing": { # 处理搜索条件
"condition": "WHERE",
# 原始搜索条件
"original_condition": "((`label`.`subject_id` = 11) and (`label`.`is_deleted` = 1) and (`label`.`label_id` in (197750,197637,197947)) and (`q`.`subject_id` = 11) and (`q`.`parent_id` = 0) and (`q`.`is_deleted` = 0) and (`q`.`quality` = 4) and (`label`.`question_id` = `q`.`question_id`))",
"steps": [
{
# 等值传递转换
"transformation": "equality_propagation",
"resulting_condition": "((`label`.`label_id` in (197750,197637,197947)) and multiple equal(11, `label`.`subject_id`) and multiple equal(1, `label`.`is_deleted`) and multiple equal(11, `q`.`subject_id`) and multiple equal(0, `q`.`parent_id`) and multiple equal(0, `q`.`is_deleted`) and multiple equal(4, `q`.`quality`) and multiple equal(`label`.`question_id`, `q`.`question_id`))"
},
{
# 常量传递转换
"transformation": "constant_propagation",
"resulting_condition": "((`label`.`label_id` in (197750,197637,197947)) and multiple equal(11, `label`.`subject_id`) and multiple equal(1, `label`.`is_deleted`) and multiple equal(11, `q`.`subject_id`) and multiple equal(0, `q`.`parent_id`) and multiple equal(0, `q`.`is_deleted`) and multiple equal(4, `q`.`quality`) and multiple equal(`label`.`question_id`, `q`.`question_id`))"
},
{
# 去除无用条件
"transformation": "trivial_condition_removal",
"resulting_condition": "((`label`.`label_id` in (197750,197637,197947)) and multiple equal(11, `label`.`subject_id`) and multiple equal(1, `label`.`is_deleted`) and multiple equal(11, `q`.`subject_id`) and multiple equal(0, `q`.`parent_id`) and multiple equal(0, `q`.`is_deleted`) and multiple equal(4, `q`.`quality`) and multiple equal(`label`.`question_id`, `q`.`question_id`))"
}
]
}
},
{
# 替换虚拟生成列
"substitute_generated_columns": {
}
},
{
# 表的依赖信息
"table_dependencies": [
{
"table": "`tb_question` `q`",
"row_may_be_null": false,
"map_bit": 0,
"depends_on_map_bits": [
]
},
{
"table": "`tb_question_label` `label`",
"row_may_be_null": false,
"map_bit": 1,
"depends_on_map_bits": [
]
}
]
},
{
"ref_optimizer_key_uses": [
{
"table": "`tb_question` `q`",
"field": "question_id",
"equals": "`label`.`question_id`",
"null_rejecting": false
},
{
"table": "`tb_question` `q`",
"field": "parent_id",
"equals": "0",
"null_rejecting": false
},
{
"table": "`tb_question_label` `label`",
"field": "question_id",
"equals": "`q`.`question_id`",
"null_rejecting": false
}
]
},
{
# 预估不同单表访问方法的访问成本
"rows_estimation": [
{
"table": "`tb_question` `q`",
"const_keys_added": {
"keys": [
"uk_question"
],
"cause": "distinct"
},
"range_analysis": {
"table_scan": { # 全表扫描的行数及成本
"rows": 566210,
"cost": 118915
},
# 分析可能使用的索引
"potential_range_indexes": [
{
"index": "PRIMARY", # 主键不可用
"usable": false,
"cause": "not_applicable"
},
{
"index": "uk_question", # uk_question可能被使用
"usable": true,
"key_parts": [
"question_id"
]
},
{
"index": "idx_parent", # idx_parent可能被使用
"usable": true,
"key_parts": [
"parent_id",
"id"
]
},
{
"index": "idx_adapt_from", # idx_adapt_from不可被使用
"usable": false,
"cause": "not_applicable"
}
],
"setup_range_conditions": [
],
"group_index_range": {
"chosen": false,
"cause": "not_single_table"
},
# 分析各种可能使用的索引的成本
"analyzing_range_alternatives": {
"range_scan_alternatives": [
{
# 使用idx_parent的成本分析
"index": "idx_parent",
"ranges": [
"0 <= parent_id <= 0"
],
"index_dives_for_eq_ranges": true, # 是否使用index dive
"rowid_ordered": true, # 使用该索引获取的记录是否按照主键排序
"using_mrr": false, # 是否使用mrr
"index_only": false, # 是否是索引覆盖访问
"rows": 283105, # 使用该索引获取的记录条数
"cost": 339727, # 使用该索引的成本
"chosen": false, # 是否选择该索引
"cause": "cost"
}
],
# 分析使用索引合并的成本
"analyzing_roworder_intersect": {
"usable": false,
"cause": "too_few_roworder_scans"
}
}
}
},
{
"table": "`tb_question_label` `label`",
"range_analysis": {
"table_scan": {
"rows": 685400,
"cost": 140576
},
"potential_range_indexes": [
{
"index": "PRIMARY",
"usable": false,
"cause": "not_applicable"
},
{
"index": "idx_label",
"usable": true,
"key_parts": [
"label_id",
"id"
]
},
{
"index": "idx_question",
"usable": false,
"cause": "not_applicable"
},
{
"index": "idx_sub_question",
"usable": false,
"cause": "not_applicable"
}
],
"setup_range_conditions": [
],
"group_index_range": {
"chosen": false,
"cause": "not_single_table"
},
"analyzing_range_alternatives": {
"range_scan_alternatives": [
{
"index": "idx_label",
"ranges": [
"197637 <= label_id <= 197637",
"197750 <= label_id <= 197750",
"197947 <= label_id <= 197947"
],
"index_dives_for_eq_ranges": true,
"rowid_ordered": false,
"using_mrr": false,
"index_only": false,
"rows": 3,
"cost": 6.61,
"chosen": true
}
],
"analyzing_roworder_intersect": {
"usable": false,
"cause": "too_few_roworder_scans"
}
},
# 对于上述单表查询tb_question_label最优的访问方法
"chosen_range_access_summary": {
"range_access_plan": {
"type": "range_scan",
"index": "idx_label",
"rows": 3,
"ranges": [
"197637 <= label_id <= 197637",
"197750 <= label_id <= 197750",
"197947 <= label_id <= 197947"
]
},
"rows_for_plan": 3,
"cost_for_plan": 6.61,
"chosen": true
}
}
}
]
},
{
# 分析各种可能的执行计划（对多表查询这可能有很多种不同的方案）
"considered_execution_plans": [
{
"plan_prefix": [
],
"table": "`tb_question_label` `label`",
"best_access_path": {
"considered_access_paths": [
{
"access_type": "ref",
"index": "idx_question",
"usable": false,
"chosen": false
},
{
"rows_to_scan": 3,
"access_type": "range",
"range_details": {
"used_index": "idx_label"
},
"resulting_rows": 0.05,
"cost": 7.21,
"chosen": true
}
]
},
"condition_filtering_pct": 100,
"rows_for_plan": 0.05,
"cost_for_plan": 7.21,
"rest_of_plan": [
{
"plan_prefix": [
"`tb_question_label` `label`"
],
"table": "`tb_question` `q`",
"best_access_path": {
"considered_access_paths": [
{
"access_type": "eq_ref",
"index": "uk_question",
"rows": 1,
"cost": 0.06,
"chosen": true
},
{
"access_type": "ref",
"index": "idx_parent",
"chosen": false,
"cause": "heuristic_eqref_already_found"
},
{
"access_type": "scan",
"cost": 118913,
"rows": 566210,
"chosen": false,
"cause": "cost"
}
]
},
"condition_filtering_pct": 100,
"rows_for_plan": 0.05,
"cost_for_plan": 7.27,
"chosen": true
}
]
},
{
"plan_prefix": [
],
"table": "`tb_question` `q`",
"best_access_path": {
"considered_access_paths": [
{
"access_type": "ref",
"index": "uk_question",
"usable": false,
"chosen": false
},
{
"access_type": "ref",
"index": "idx_parent",
"rows": 283105,
"cost": 73634,
"chosen": true
},
{
"rows_to_scan": 566210,
"access_type": "scan",
"resulting_rows": 283.11,
"cost": 118913,
"chosen": false
}
]
},
"condition_filtering_pct": 0.1,
"rows_for_plan": 283.11,
"cost_for_plan": 73634,
"pruned_by_cost": true
}
]
},
{
# 尝试给查询添加一些其他的查询条件
"attaching_conditions_to_tables": {
"original_condition": "((`q`.`question_id` = `label`.`question_id`) and (`q`.`quality` = 4) and (`q`.`is_deleted` = 0) and (`q`.`parent_id` = 0) and (`q`.`subject_id` = 11) and (`label`.`is_deleted` = 1) and (`label`.`subject_id` = 11) and (`label`.`label_id` in (197750,197637,197947)))",
"attached_conditions_computation": [
],
"attached_conditions_summary": [
{
"table": "`tb_question_label` `label`",
"attached": "((`label`.`is_deleted` = 1) and (`label`.`subject_id` = 11) and (`label`.`label_id` in (197750,197637,197947)))"
},
{
"table": "`tb_question` `q`",
"attached": "((`q`.`quality` = 4) and (`q`.`is_deleted` = 0) and (`q`.`parent_id` = 0) and (`q`.`subject_id` = 11))"
}
]
}
},
{
# 再稍稍的改进一下执行计划
"refine_plan": [
{
"table": "`tb_question_label` `label`",
"pushed_index_condition": "(`label`.`label_id` in (197750,197637,197947))",
"table_condition_attached": "((`label`.`is_deleted` = 1) and (`label`.`subject_id` = 11))"
},
{
"table": "`tb_question` `q`"
}
]
}
]
}
},
{
"join_execution": {
"select#": 1,
"steps": [
{
"creating_tmp_table": {
"tmp_table_info": {
"table": "intermediate_tmp_table",
"row_length": 9,
"key_length": 8,
"unique_constraint": false,
"location": "memory (heap)",
"row_limit_estimate": 3000
}
}
}
]
}
}
]
}
（2）执行计划二的执行过程
{
"steps": [
{
"join_preparation": { # prepare阶段
"select#": 1,
"steps": [
{
"IN_uses_bisection": true
},
{
"expanded_query": "/* select#1 */ select distinct `q`.`question_id` AS `question_id` from (`tb_question` `q` join `tb_question_label` `label` on((`label`.`question_id` = `q`.`question_id`))) where ((`label`.`subject_id` = 11) and (`label`.`is_deleted` = 0) and (`label`.`label_id` in (197049,187007,187006)) and (`q`.`subject_id` = 11) and (`q`.`parent_id` = 0) and (`q`.`is_deleted` = 0) and (`q`.`quality` = 4)) limit 3000"
},
{
"transformations_to_nested_joins": {
"transformations": [
"JOIN_condition_to_WHERE",
"parenthesis_removal"
],
"expanded_query": "/* select#1 */ select distinct `q`.`question_id` AS `question_id` from `tb_question` `q` join `tb_question_label` `label` where ((`label`.`subject_id` = 11) and (`label`.`is_deleted` = 0) and (`label`.`label_id` in (197049,187007,187006)) and (`q`.`subject_id` = 11) and (`q`.`parent_id` = 0) and (`q`.`is_deleted` = 0) and (`q`.`quality` = 4) and (`label`.`question_id` = `q`.`question_id`)) limit 3000"
}
}
]
}
},
{
"join_optimization": { # optimize阶段
"select#": 1,
"steps": [
{
"condition_processing": { # 处理搜索条件
"condition": "WHERE",
# 原始搜索条件
"original_condition": "((`label`.`subject_id` = 11) and (`label`.`is_deleted` = 0) and (`label`.`label_id` in (197049,187007,187006)) and (`q`.`subject_id` = 11) and (`q`.`parent_id` = 0) and (`q`.`is_deleted` = 0) and (`q`.`quality` = 4) and (`label`.`question_id` = `q`.`question_id`))",
"steps": [
{
# 等值传递转换
"transformation": "equality_propagation",
"resulting_condition": "((`label`.`label_id` in (197049,187007,187006)) and multiple equal(11, `label`.`subject_id`) and multiple equal(0, `label`.`is_deleted`) and multiple equal(11, `q`.`subject_id`) and multiple equal(0, `q`.`parent_id`) and multiple equal(0, `q`.`is_deleted`) and multiple equal(4, `q`.`quality`) and multiple equal(`label`.`question_id`, `q`.`question_id`))"
},
{
# 常量传递转换
"transformation": "constant_propagation",
"resulting_condition": "((`label`.`label_id` in (197049,187007,187006)) and multiple equal(11, `label`.`subject_id`) and multiple equal(0, `label`.`is_deleted`) and multiple equal(11, `q`.`subject_id`) and multiple equal(0, `q`.`parent_id`) and multiple equal(0, `q`.`is_deleted`) and multiple equal(4, `q`.`quality`) and multiple equal(`label`.`question_id`, `q`.`question_id`))"
},
{
# 去除无用条件
"transformation": "trivial_condition_removal",
"resulting_condition": "((`label`.`label_id` in (197049,187007,187006)) and multiple equal(11, `label`.`subject_id`) and multiple equal(0, `label`.`is_deleted`) and multiple equal(11, `q`.`subject_id`) and multiple equal(0, `q`.`parent_id`) and multiple equal(0, `q`.`is_deleted`) and multiple equal(4, `q`.`quality`) and multiple equal(`label`.`question_id`, `q`.`question_id`))"
}
]
}
},
{
"substitute_generated_columns": {
}
},
{
# 替换虚拟生成列
"table_dependencies": [
{
"table": "`tb_question` `q`",
"row_may_be_null": false,
"map_bit": 0,
"depends_on_map_bits": [
]
},
{
"table": "`tb_question_label` `label`",
"row_may_be_null": false,
"map_bit": 1,
"depends_on_map_bits": [
]
}
]
},
{
"ref_optimizer_key_uses": [
{
"table": "`tb_question` `q`",
"field": "question_id",
"equals": "`label`.`question_id`",
"null_rejecting": false
},
{
"table": "`tb_question` `q`",
"field": "parent_id",
"equals": "0",
"null_rejecting": false
},
{
"table": "`tb_question_label` `label`",
"field": "question_id",
"equals": "`q`.`question_id`",
"null_rejecting": false
}
]
},
{
# 预估不同单表访问方法的访问成本
"rows_estimation": [
{
"table": "`tb_question` `q`",
"const_keys_added": {
"keys": [
"uk_question"
],
"cause": "distinct"
},
"range_analysis": {
"table_scan": { # 全表扫描的行数及成本
"rows": 566210,
"cost": 118915
},
# 分析可能使用的索引
"potential_range_indexes": [
{
"index": "PRIMARY", # 主键不可用
"usable": false,
"cause": "not_applicable"
},
{
"index": "uk_question", # uk_question可能被使用
"usable": true,
"key_parts": [
"question_id"
]
},
{
"index": "idx_parent", # idx_parent可能被使用
"usable": true,
"key_parts": [
"parent_id",
"id"
]
},
{
"index": "idx_adapt_from", # idx_adapt_from不可被使用
"usable": false,
"cause": "not_applicable"
}
],
"setup_range_conditions": [
],
"group_index_range": {
"chosen": false,
"cause": "not_single_table"
},
# 分析各种可能使用的索引的成本
"analyzing_range_alternatives": {
"range_scan_alternatives": [
{
# 使用idx_parent的成本分析
"index": "idx_parent",
"ranges": [
"0 <= parent_id <= 0"
],
"index_dives_for_eq_ranges": true, # 是否使用index dive
"rowid_ordered": true, # 使用该索引获取的记录是否按照主键排序
"using_mrr": false, # 是否使用mrr
"index_only": false, # 是否是索引覆盖访问
"rows": 283105, # 使用该索引获取的记录条数
"cost": 339727, # 使用该索引的成本
"chosen": false, # 是否选择该索引
"cause": "cost"
}
],
# 分析使用索引合并的成本
"analyzing_roworder_intersect": {
"usable": false,
"cause": "too_few_roworder_scans"
}
}
}
},
{
"table": "`tb_question_label` `label`",
"range_analysis": {
"table_scan": {
"rows": 685400,
"cost": 140576
},
"potential_range_indexes": [
{
"index": "PRIMARY",
"usable": false,
"cause": "not_applicable"
},
{
"index": "idx_label",
"usable": true,
"key_parts": [
"label_id",
"id"
]
},
{
"index": "idx_question",
"usable": false,
"cause": "not_applicable"
},
{
"index": "idx_sub_question",
"usable": false,
"cause": "not_applicable"
}
],
"setup_range_conditions": [
],
"group_index_range": {
"chosen": false,
"cause": "not_single_table"
},
"analyzing_range_alternatives": {
"range_scan_alternatives": [
{
"index": "idx_label",
"ranges": [
"187006 <= label_id <= 187006",
"187007 <= label_id <= 187007",
"197049 <= label_id <= 197049"
],
"index_dives_for_eq_ranges": true,
"rowid_ordered": false,
"using_mrr": false,
"index_only": false,
"rows": 53010,
"cost": 63615,
"chosen": true
}
],
"analyzing_roworder_intersect": {
"usable": false,
"cause": "too_few_roworder_scans"
}
},
# 对于上述单表查询tb_question_label最优的访问方法
"chosen_range_access_summary": {
"range_access_plan": {
"type": "range_scan",
"index": "idx_label",
"rows": 53010,
"ranges": [
"187006 <= label_id <= 187006",
"187007 <= label_id <= 187007",
"197049 <= label_id <= 197049"
]
},
"rows_for_plan": 53010,
"cost_for_plan": 63615,
"chosen": true
}
}
}
]
},
{
# 分析各种可能的执行计划（对多表查询这可能有很多种不同的方案）
"considered_execution_plans": [
{
"plan_prefix": [
],
"table": "`tb_question_label` `label`",
"best_access_path": {
"considered_access_paths": [
{
"access_type": "ref",
"index": "idx_question",
"usable": false,
"chosen": false
},
{
"rows_to_scan": 53010,
"access_type": "range",
"range_details": {
"used_index": "idx_label"
},
"resulting_rows": 530.1,
"cost": 74217,
"chosen": true
}
]
},
"condition_filtering_pct": 100,
"rows_for_plan": 530.1,
"cost_for_plan": 74217,
"rest_of_plan": [
{
"plan_prefix": [
"`tb_question_label` `label`"
],
"table": "`tb_question` `q`",
"best_access_path": {
"considered_access_paths": [
{
"access_type": "eq_ref",
"index": "uk_question",
"rows": 1,
"cost": 636.12,
"chosen": true
},
{
"access_type": "ref",
"index": "idx_parent",
"chosen": false,
"cause": "heuristic_eqref_already_found"
},
{
"access_type": "scan",
"cost": 118913,
"rows": 566210,
"chosen": false,
"cause": "cost"
}
]
},
"condition_filtering_pct": 5,
"rows_for_plan": 26.505,
"cost_for_plan": 74853,
"chosen": true
}
]
},
{
"plan_prefix": [
],
"table": "`tb_question` `q`",
"best_access_path": {
"considered_access_paths": [
{
"access_type": "ref",
"index": "uk_question",
"usable": false,
"chosen": false
},
{
"access_type": "ref",
"index": "idx_parent",
"rows": 283105,
"cost": 73634,
"chosen": true
},
{
"rows_to_scan": 566210,
"access_type": "scan",
"resulting_rows": 283.11,
"cost": 118913,
"chosen": false
}
]
},
"condition_filtering_pct": 0.1,
"rows_for_plan": 283.11,
"cost_for_plan": 73634,
"rest_of_plan": [
{
"plan_prefix": [
"`tb_question` `q`"
],
"table": "`tb_question_label` `label`",
"best_access_path": {
"considered_access_paths": [
{
"access_type": "ref",
"index": "idx_question",
"rows": 1.4988,
"cost": 509.18,
"chosen": true
},
{
"access_type": "range",
"range_details": {
"used_index": "idx_label"
},
"cost": 74217,
"rows": 53010,
"chosen": false,
"cause": "cost"
}
]
},
"condition_filtering_pct": 3.336,
"rows_for_plan": 14.155,
"cost_for_plan": 74143,
"chosen": true
}
]
}
]
},
{
# 尝试给查询添加一些其他的查询条件
"attaching_conditions_to_tables": {
"original_condition": "((`label`.`question_id` = `q`.`question_id`) and (`q`.`quality` = 4) and (`q`.`is_deleted` = 0) and (`q`.`parent_id` = 0) and (`q`.`subject_id` = 11) and (`label`.`is_deleted` = 0) and (`label`.`subject_id` = 11) and (`label`.`label_id` in (197049,187007,187006)))",
"attached_conditions_computation": [
],
"attached_conditions_summary": [
{
"table": "`tb_question` `q`",
"attached": "((`q`.`quality` = 4) and (`q`.`is_deleted` = 0) and (`q`.`subject_id` = 11))"
},
{
"table": "`tb_question_label` `label`",
"attached": "((`label`.`is_deleted` = 0) and (`label`.`subject_id` = 11) and (`label`.`label_id` in (197049,187007,187006)))"
}
]
}
},
{
# 再稍稍的改进一下执行计划
"refine_plan": [
{
"table": "`tb_question` `q`"
},
{
"table": "`tb_question_label` `label`"
}
]
}
]
}
},
{
"join_explain
(trace太长，后面文本字节被忽略)
（3）总结
通过（1）、（2）的optimizer_trace分析，可以看到，执行计划的变更，是根据连接查询的成本来考量的。
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