Basic Optimizer Trace Example
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MariaDB> set optimizer_trace=’enabled=on’; MariaDB> select * from t1 where a<10; MariaDB> select * from information_schema.optimizer_trace limit 1\G *************************** 1. row *************************** QUERY: select * from t1 where a<10 TRACE: { "steps": [ { "join_preparation": { "select_id": 1, "steps": [ { "expanded_query": "select t1.a AS a,t1.b AS b,t1.c AS c from t1 where t1.a < 10" } ] } }, { "join_optimization": { "select_id": 1, "steps": [ { "condition_processing": { "condition": "WHERE", "original_condition": "t1.a < 10", "steps": [ { "transformation": "equality_propagation", "resulting_condition": "t1.a < 10" }, { "transformation": "constant_propagation", "resulting_condition": "t1.a < 10" }, { "transformation": "trivial_condition_removal", "resulting_condition": "t1.a < 10" } ] } }, { "table_dependencies": [ { "table": "t1", "row_may_be_null": false, "map_bit": 0, "depends_on_map_bits": [] } ] }, { "ref_optimizer_key_uses": [] }, { "rows_estimation": [ { "table": "t1", "range_analysis": { "table_scan": { "rows": 1000, "cost": 206.1 }, "potential_range_indexes": [ { "index": "a", "usable": true, "key_parts": ["a"] }, { "index": "b", "usable": false, "cause": "not applicable" } ], "setup_range_conditions": [], "group_index_range": { "chosen": false, "cause": "no group by or distinct" }, "analyzing_range_alternatives": { "range_scan_alternatives": [ { "index": "a", "ranges": ["(NULL) < (a) < (10)"], "rowid_ordered": false, "using_mrr": false, "index_only": false, "rows": 10, "cost": 13.751, "chosen": true } ], "analyzing_roworder_intersect": { "cause": "too few roworder scans" }, "analyzing_index_merge_union": [] }, "chosen_range_access_summary": { "range_access_plan": { "type": "range_scan", "index": "a", "rows": 10, "ranges": ["(NULL) < (a) < (10)"] }, "rows_for_plan": 10, "cost_for_plan": 13.751, "chosen": true } } }, { "selectivity_for_indexes": [ { "index_name": "a", "selectivity_from_index": 0.01 } ], "selectivity_for_columns": [], "cond_selectivity": 0.01 } ] }, { "considered_execution_plans": [ { "plan_prefix": [], "table": "t1", "best_access_path": { "considered_access_paths": [ { "access_type": "range", "resulting_rows": 10, "cost": 13.751, "chosen": true } ] } } ] }, { "attaching_conditions_to_tables": { "original_condition": "t1.a < 10", "attached_conditions_computation": [], "attached_conditions_summary": [ { "table": "t1", "attached": "t1.a < 10" } ] } } ] } }, { "join_execution": { "select_id": 1, "steps": [] } } ] } MISSING_BYTES_BEYOND_MAX_MEM_SIZE: 0 INSUFFICIENT_PRIVILEGES: 0
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