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Change cost for REF to take into account cost for 1 extra key read_next
The main difference in code path between EQ_REF and REF is that for REF we have to do an extra read_next on the index to check that there is no more matching rows. Before this patch we added a preference of EQ_REF by ensuring that REF would always estimate to find at least 2 rows. This patch adds the cost of the extra key read_next to REF access and removes the code that limited REF to at least 2 rows. For some queries this can have a big effect as the total estimated rows will be halved for each REF table with 1 rows. multi_range cost calculations are also changed to take into account the difference between EQ_REF and REF. The effect of the patch to the test suite: - About 80 test case changed - Almost all changes where for EXPLAIN where estimated rows for REF where changed from 2 to 1. - A few test cases using explain extended had a change of 'filtered'. This is because of the estimated rows are now closer to the calculated selectivity. - A very few test had a change of table order. This is because the change of estimated rows from 2 to 1 or the small cost change for REF (main.subselect_sj_jcl6, main.group_by, main.dervied_cond_pushdown, main.distinct, main.join_nested, main.order_by, main.join_cache) - No key statistics and the estimated rows are now smaller which cased estimated filtering to be lower. (main.subselect_sj_mat) - The number of total rows are halved. (main.derived_cond_pushdown) - Plans with 1 row changed to use RANGE instead of REF. (main.group_min_max) - ALL changed to REF (main.key_diff) - Key changed from ref + index_only to PRIMARY key for InnoDB, as OPTIMIZER_ROW_LOOKUP_COST + OPTIMIZER_ROW_NEXT_FIND_COST is smaller than OPTIMIZER_KEY_LOOKUP_COST + OPTIMIZER_KEY_NEXT_FIND_COST. (main.join_outer_innodb) - Cost changes printouts (main.opt_trace*) - Result order change (innodb_gis.rtree)
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Monty
@ -689,13 +689,13 @@ from ancestor_couple_ids c, coupled_ancestors h, coupled_ancestors w
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where c.h_id = h.id and c.w_id= w.id;
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id select_type table type possible_keys key key_len ref rows filtered Extra
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1 PRIMARY <derived2> ALL NULL NULL NULL NULL 2 100.00 Using where
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1 PRIMARY <derived3> ref key0 key0 5 c.h_id 2 100.00
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1 PRIMARY <derived3> ref key0 key0 5 c.w_id 2 100.00
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1 PRIMARY <derived3> ref key0 key0 5 c.h_id 1 100.00
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1 PRIMARY <derived3> ref key0 key0 5 c.w_id 1 100.00
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3 DERIVED folks ALL NULL NULL NULL NULL 12 100.00 Using where
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4 RECURSIVE UNION p ALL NULL NULL NULL NULL 12 100.00 Using where
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4 RECURSIVE UNION <derived2> ref key0 key0 5 test.p.id 2 100.00
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4 RECURSIVE UNION <derived2> ref key0 key0 5 test.p.id 1 100.00
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5 RECURSIVE UNION p ALL NULL NULL NULL NULL 12 100.00 Using where
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5 RECURSIVE UNION <derived2> ref key0 key0 5 test.p.id 2 100.00
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5 RECURSIVE UNION <derived2> ref key0 key0 5 test.p.id 1 100.00
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NULL UNION RESULT <union3,4,5> ALL NULL NULL NULL NULL NULL NULL
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2 DERIVED <derived3> ALL NULL NULL NULL NULL 12 100.00 Using where
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Warnings:
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@ -1238,9 +1238,9 @@ id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY <derived2> ALL NULL NULL NULL NULL 12
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2 DERIVED folks ALL NULL NULL NULL NULL 12 Using where
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3 RECURSIVE UNION p ALL PRIMARY NULL NULL NULL 12
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3 RECURSIVE UNION <derived2> ref key0 key0 5 test.p.id 2
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3 RECURSIVE UNION <derived2> ref key0 key0 5 test.p.id 1
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4 RECURSIVE UNION p ALL PRIMARY NULL NULL NULL 12
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4 RECURSIVE UNION <derived2> ref key0 key0 5 test.p.id 2
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4 RECURSIVE UNION <derived2> ref key0 key0 5 test.p.id 1
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NULL UNION RESULT <union2,3,4> ALL NULL NULL NULL NULL NULL
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with recursive
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ancestors
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@ -3210,7 +3210,7 @@ id select_type table type possible_keys key key_len ref rows filtered Extra
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1 PRIMARY <derived2> ALL NULL NULL NULL NULL 16 100.00
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2 DERIVED a ALL NULL NULL NULL NULL 16 100.00 Using where
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3 RECURSIVE UNION b ALL NULL NULL NULL NULL 16 100.00 Using where
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3 RECURSIVE UNION <derived2> ref key0 key0 35 test.b.departure 2 100.00
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3 RECURSIVE UNION <derived2> ref key0 key0 35 test.b.departure 1 100.00
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4 DEPENDENT SUBQUERY <derived2> ALL NULL NULL NULL NULL 16 100.00 Using where
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NULL UNION RESULT <union2,3> ALL NULL NULL NULL NULL NULL NULL
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Warnings:
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@ -3313,9 +3313,9 @@ id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY <derived2> ALL NULL NULL NULL NULL 15 Using filesort
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2 DERIVED t2 ALL NULL NULL NULL NULL 15 Using where
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3 RECURSIVE UNION t2 ALL NULL NULL NULL NULL 15 Using where
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3 RECURSIVE UNION <derived2> ref key0 key0 5 test.t2.id 2
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3 RECURSIVE UNION <derived2> ref key0 key0 5 test.t2.id 1
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4 RECURSIVE UNION t2 ALL NULL NULL NULL NULL 15 Using where
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4 RECURSIVE UNION <derived2> ref key0 key0 5 test.t2.id 2
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4 RECURSIVE UNION <derived2> ref key0 key0 5 test.t2.id 1
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NULL UNION RESULT <union2,3,4> ALL NULL NULL NULL NULL NULL
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DROP TABLE t1,t2;
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set tmp_memory_table_size=default;
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@ -4168,7 +4168,7 @@ id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY NULL NULL NULL NULL NULL NULL NULL No tables used
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2 DERIVED s ALL NULL NULL NULL NULL 4
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3 RECURSIVE UNION t1 ALL NULL NULL NULL NULL 4 Using where
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3 RECURSIVE UNION <derived2> ref key0 key0 9 test.t1.c 2
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3 RECURSIVE UNION <derived2> ref key0 key0 9 test.t1.c 1
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NULL UNION RESULT <union2,3> ALL NULL NULL NULL NULL NULL
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4 UNION <derived2> ALL NULL NULL NULL NULL 4
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with recursive r_cte as
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@ -4292,7 +4292,7 @@ ANALYZE
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"ref": ["test.t1.c"],
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"loops": 4,
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"r_loops": 4,
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"rows": 2,
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"rows": 1,
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"r_rows": 0.5,
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"cost": "REPLACED",
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"r_table_time_ms": "REPLACED",
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@ -4545,7 +4545,7 @@ NULL UNION RESULT <union4,5> ALL NULL NULL NULL NULL NULL
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3 DERIVED h ALL NULL NULL NULL NULL 12 Using where; Using join buffer (flat, BNL join)
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3 DERIVED w ALL NULL NULL NULL NULL 12 Using where; Using join buffer (incremental, BNL join)
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2 RECURSIVE UNION h ALL NULL NULL NULL NULL 12 Using where
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2 RECURSIVE UNION <derived4> ref key0 key0 5 test.h.id 2
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2 RECURSIVE UNION <derived4> ref key0 key0 5 test.h.id 1
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2 RECURSIVE UNION w ALL NULL NULL NULL NULL 12 Using where; Using join buffer (flat, BNL join)
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NULL UNION RESULT <union3,2> ALL NULL NULL NULL NULL NULL
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prepare stmt from "with recursive
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@ -4643,7 +4643,7 @@ id select_type table type possible_keys key key_len ref rows Extra
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5 RECURSIVE UNION <derived2> ALL NULL NULL NULL NULL 2
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NULL UNION RESULT <union3,4,5> ALL NULL NULL NULL NULL NULL
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2 DERIVED h ALL NULL NULL NULL NULL 12 Using where
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2 DERIVED <derived3> ref key0 key0 5 test.h.id 2
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2 DERIVED <derived3> ref key0 key0 5 test.h.id 1
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2 DERIVED w ALL NULL NULL NULL NULL 12 Using where; Using join buffer (flat, BNL join)
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prepare stmt from "with recursive
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ancestor_couples(h_id, h_name, h_dob, h_father, h_mother,
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