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Bug#50939: Loose Index Scan unduly relies on engine to

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remember range endpoints

The Loose Index Scan optimization keeps track of a sequence
of intervals. For the current interval it maintains the
current interval's endpoints. But the maximum endpoint was
not stored in the SQL layer; rather, it relied on the
storage engine to retain this value in-between reads. By
coincidence this holds for MyISAM and InnoDB. Not for the
partitioning engine, however.

Fixed by making the key values iterator 
(QUICK_RANGE_SELECT) keep track of the current maximum endpoint.
This is also more efficient as we save a call through the
handler API in case of open-ended intervals.

The code to calculate endpoints was extracted into 
separate methods in QUICK_RANGE_SELECT, and it was possible to
get rid of some code duplication as part of fix.
This commit is contained in:
Martin Hansson
2010-05-10 09:23:23 +02:00
parent bea068326f
commit 1c5200f67d
4 changed files with 199 additions and 62 deletions
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44
mysql-test/r/range.result
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@ -1653,4 +1653,48 @@ a b
0 0
1 1
DROP TABLE t1;
#
# Bug#50939: Loose Index Scan unduly relies on engine to remember range
# endpoints
#
CREATE TABLE t1 (
a INT,
b INT,
KEY ( a, b )
) PARTITION BY HASH (a) PARTITIONS 1;
CREATE TABLE t2 (
a INT,
b INT,
KEY ( a, b )
);
INSERT INTO t1 VALUES (1, 1), (2, 2), (3, 3), (4, 4), (5, 5);
INSERT INTO t1 SELECT a + 5, b + 5 FROM t1;
INSERT INTO t1 SELECT a + 10, b + 10 FROM t1;
INSERT INTO t1 SELECT a + 20, b + 20 FROM t1;
INSERT INTO t1 SELECT a + 40, b + 40 FROM t1;
INSERT INTO t2 SELECT * FROM t1;
# plans should be identical
EXPLAIN SELECT a, MAX(b) FROM t1 WHERE a IN (10,100) GROUP BY a;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 range a a 5 NULL 1 Using where; Using index for group-by
EXPLAIN SELECT a, MAX(b) FROM t2 WHERE a IN (10,100) GROUP BY a;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t2 range a a 5 NULL 2 Using where; Using index for group-by
FLUSH status;
SELECT a, MAX(b) FROM t1 WHERE a IN (10, 100) GROUP BY a;
a MAX(b)
10 10
# Should be no more than 4 reads.
SHOW status LIKE 'handler_read_key';
Variable_name Value
Handler_read_key 4
FLUSH status;
SELECT a, MAX(b) FROM t2 WHERE a IN (10, 100) GROUP BY a;
a MAX(b)
10 10
# Should be no more than 4 reads.
SHOW status LIKE 'handler_read_key';
Variable_name Value
Handler_read_key 4
DROP TABLE t1, t2;
End of 5.1 tests