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3fa99f0c0e
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)
35 lines
1 KiB
Text
35 lines
1 KiB
Text
CREATE TABLE t1(a INT PRIMARY KEY, b VARCHAR(40), c INT, INDEX(b,c))
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ENGINE=InnoDB;
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INSERT INTO t1 VALUES (1,'1',1),(2,'2',1),(3,'3',1);
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SET @save_locks= @@GLOBAL.innodb_status_output_locks;
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SET GLOBAL INNODB_STATUS_OUTPUT_LOCKS = 'ON';
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SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;
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BEGIN;
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DELETE FROM t1 WHERE b='2' AND c=2;
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SHOW ENGINE INNODB STATUS;
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Type Name Status
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InnoDB 2 lock struct(s), 1 row lock(s)
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ROLLBACK;
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SET TRANSACTION ISOLATION LEVEL REPEATABLE READ;
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BEGIN;
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DELETE FROM t1 WHERE b='2' AND c=2;
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SHOW ENGINE INNODB STATUS;
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Type Name Status
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InnoDB 2 lock struct(s), 1 row lock(s)
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ROLLBACK;
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SET TRANSACTION ISOLATION LEVEL READ COMMITTED;
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BEGIN;
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DELETE FROM t1 WHERE b='2' AND c=2;
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SHOW ENGINE INNODB STATUS;
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Type Name Status
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InnoDB 1 lock struct(s), 0 row lock(s)
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ROLLBACK;
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SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;
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BEGIN;
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DELETE FROM t1 WHERE b='2' AND c=2;
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SHOW ENGINE INNODB STATUS;
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Type Name Status
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InnoDB 1 lock struct(s), 0 row lock(s)
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ROLLBACK;
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SET GLOBAL INNODB_STATUS_OUTPUT_LOCKS = @save_locks;
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DROP TABLE t1;
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