mysql中cost对比测试
1.数据库表
复制表
2.执行select c_id from customer where c_discount = 0.35;后，explain对比
3.optimizer_trace比较
原表
{
"steps": [
{
"join_preparation": {
"select#": 1,
"steps": [
{
"expanded_query": "/* select#1 */ select `customer`.`c_id` AS `c_id` from `customer` where (`customer`.`c_discount` = 0.35)"
}
]
}
},
{
"join_optimization": {
"select#": 1,
"steps": [
{
"condition_processing": {
"condition": "WHERE",
"original_condition": "(`customer`.`c_discount` = 0.35)",
"steps": [
{
"transformation": "equality_propagation",
"resulting_condition": "multiple equal(0.35, `customer`.`c_discount`)"
},
{
"transformation": "constant_propagation",
"resulting_condition": "multiple equal(0.35, `customer`.`c_discount`)"
},
{
"transformation": "trivial_condition_removal",
"resulting_condition": "multiple equal(0.35, `customer`.`c_discount`)"
}
]
}
},
{
"substitute_generated_columns": {
}
},
{
"table_dependencies": [
{
"table": "`customer`",
"row_may_be_null": false,
"map_bit": 0,
"depends_on_map_bits": [
]
}
]
},
{
"ref_optimizer_key_uses": [
]
},
{
"rows_estimation": [
{
"table": "`customer`",
"table_scan": {
"rows": 289371,
"cost": 11504
}
}
]
},
{
"considered_execution_plans": [
{
"plan_prefix": [
],
"table": "`customer`",
"best_access_path": {
"considered_access_paths": [
{
"rows_to_scan": 289371,
"filtering_effect": [
],
"final_filtering_effect": 0.1,
"access_type": "scan",
"resulting_rows": 28937,
"cost": 40441,
"chosen": true
}
]
},
"condition_filtering_pct": 100,
"rows_for_plan": 28937,
"cost_for_plan": 40441,
"chosen": true
}
]
},
{
"attaching_conditions_to_tables": {
"original_condition": "(`customer`.`c_discount` = 0.35)",
"attached_conditions_computation": [
],
"attached_conditions_summary": [
{
"table": "`customer`",
"attached": "(`customer`.`c_discount` = 0.35)"
}
]
}
},
{
"refine_plan": [
{
"table": "`customer`"
}
]
}
]
}
},
{
"join_explain": {
"select#": 1,
"steps": [
]
}
}
]
}
复制表
{
"steps": [
{
"join_preparation": {
"select#": 1,
"steps": [
{
"expanded_query": "/* select#1 */ select `customer_new`.`c_id` AS `c_id` from `customer_new` where (`customer_new`.`c_discount` = 0.35)"
}
]
}
},
{
"join_optimization": {
"select#": 1,
"steps": [
{
"condition_processing": {
"condition": "WHERE",
"original_condition": "(`customer_new`.`c_discount` = 0.35)",
"steps": [
{
"transformation": "equality_propagation",
"resulting_condition": "multiple equal(0.35, `customer_new`.`c_discount`)"
},
{
"transformation": "constant_propagation",
"resulting_condition": "multiple equal(0.35, `customer_new`.`c_discount`)"
},
{
"transformation": "trivial_condition_removal",
"resulting_condition": "multiple equal(0.35, `customer_new`.`c_discount`)"
}
]
}
},
{
"substitute_generated_columns": {
}
},
{
"table_dependencies": [
{
"table": "`customer_new`",
"row_may_be_null": false,
"map_bit": 0,
"depends_on_map_bits": [
]
}
]
},
{
"ref_optimizer_key_uses": [
{
"table": "`customer_new`",
"field": "c_discount",
"equals": "0.35",
"null_rejecting": false
}
]
},
{
"rows_estimation": [
{
"table": "`customer_new`",
"range_analysis": {
"table_scan": {
"rows": 285901,
"cost": 41760
},
"potential_range_indexes": [
{
"index": "PRIMARY",
"usable": false,
"cause": "not_applicable"
},
{
"index": "c_d_1",
"usable": true,
"key_parts": [
"c_discount",
"c_w_id",
"c_d_id",
"c_id"
]
}
],
"best_covering_index_scan": {
"index": "c_d_1",
"cost": 28939,
"chosen": true
},
"setup_range_conditions": [
],
"group_index_range": {
"chosen": false,
"cause": "not_group_by_or_distinct"
},
"analyzing_range_alternatives": {
"range_scan_alternatives": [
{
"index": "c_d_1",
"ranges": [
"0.35 <= c_discount <= 0.35"
],
"index_dives_for_eq_ranges": true,
"rowid_ordered": true,
"using_mrr": false,
"index_only": true,
"rows": 5822,
"cost": 590.29,
"chosen": true
}
],
"analyzing_roworder_intersect": {
"usable": false,
"cause": "too_few_roworder_scans"
}
},
"chosen_range_access_summary": {
"range_access_plan": {
"type": "range_scan",
"index": "c_d_1",
"rows": 5822,
"ranges": [
"0.35 <= c_discount <= 0.35"
]
},
"rows_for_plan": 5822,
"cost_for_plan": 590.29,
"chosen": true
}
}
}
]
},
{
"considered_execution_plans": [
{
"plan_prefix": [
],
"table": "`customer_new`",
"best_access_path": {
"considered_access_paths": [
{
"access_type": "ref",
"index": "c_d_1",
"rows": 5822,
"cost": 590.28,
"chosen": true
},
{
"access_type": "range",
"range_details": {
"used_index": "c_d_1"
},
"chosen": false,
"cause": "heuristic_index_cheaper"
}
]
},
"condition_filtering_pct": 100,
"rows_for_plan": 5822,
"cost_for_plan": 590.28,
"chosen": true
}
]
},
{
"attaching_conditions_to_tables": {
"original_condition": "(`customer_new`.`c_discount` = 0.35)",
"attached_conditions_computation": [
],
"attached_conditions_summary": [
{
"table": "`customer_new`",
"attached": null
}
]
}
},
{
"refine_plan": [
{
"table": "`customer_new`"
}
]
}
]
}
},
{
"join_explain": {
"select#": 1,
"steps": [
]
}
}
]
}
其中原表的cost
带索引表中table_scan的值
