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Bug#46454: MySQL wrong index optimisation leads to incorrect result & crashes

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Problem 1:
When the 'Using index' optimization is used, the optimizer may still - after
cost-based optimization - decide to use another index in order to avoid using
a temporary table. But when this happens, the flag to the storage engine to 
read index only (not table) was still set. Fixed by resetting the flag in the 
storage engine and TABLE structure in the above scenario, unless the new index
allows for the same optimization.
Problem 2:
When a 'ref' access method was employed by cost-based optimizer, (when the column
is non-NULLable), it was assumed that it needed no initialization if 'quick' access
methods (since they are based on range scan). When ORDER BY optimization overrides 
the decision, however, it expects to have this initialized and hence crashes. 
Fixed in 5.1 (was fixed in 6.0 already) by initializing 'quick' even when there's 
'ref' access. 

mysql-test/r/order_by.result:
  Bug#46454: Test result.
mysql-test/t/order_by.test:
  Bug#46454: Test case.
sql/sql_select.cc:
  Bug#46454: 
  Problem 1 fixed in make_join_select()
  Problem 2 fixed in test_if_skip_sort_order()
sql/table.h:
  Bug#46454: Added comment to field.
This commit is contained in:
Martin Hansson 2009-08-07 13:51:40 +02:00
parent 439e1eb0e0
commit 4c3917b6f8
4 changed files with 118 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

57
mysql-test/r/order_by.result
View File

@ -1500,3 +1500,60 @@ id1
15
16
DROP TABLE t1;
CREATE TABLE t1 (
a INT,
b INT NOT NULL,
c char(100),
KEY (b, c),
KEY (b, a, c)
)
DEFAULT CHARSET = utf8;
INSERT INTO t1 VALUES
(1, 1, 1),
(2, 2, 2),
(3, 3, 3),
(4, 4, 4),
(5, 5, 5),
(6, 6, 6),
(7, 7, 7),
(8, 8, 8),
(9, 9, 9);
INSERT INTO t1 SELECT a + 10, b, c FROM t1;
INSERT INTO t1 SELECT a + 20, b, c FROM t1;
INSERT INTO t1 SELECT a + 40, b, c FROM t1;
INSERT INTO t1 SELECT a + 80, b, c FROM t1;
INSERT INTO t1 SELECT a + 160, b, c FROM t1;
INSERT INTO t1 SELECT a + 320, b, c FROM t1;
INSERT INTO t1 SELECT a + 640, b, c FROM t1;
INSERT INTO t1 SELECT a + 1280, b, c FROM t1 LIMIT 80;
EXPLAIN
SELECT a FROM t1 WHERE b = 1 ORDER BY c DESC LIMIT 9;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 range b,b_2 b 4 NULL 226 Using where
SELECT a FROM t1 WHERE b = 1 ORDER BY c DESC LIMIT 9;
a
2071
2061
2051
2041
2031
2021
2011
2001
1991
EXPLAIN
SELECT DISTINCT a FROM t1 WHERE b = 1 ORDER BY c DESC LIMIT 0, 9;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 range b,b_2 b 4 NULL 226 Using where; Using temporary
SELECT DISTINCT a FROM t1 WHERE b = 1 ORDER BY c DESC LIMIT 0, 9;
a
2071
2061
2051
2041
2031
2021
2011
2001
1991
DROP TABLE t1;

41
mysql-test/t/order_by.test
View File

@ -1361,3 +1361,44 @@ DROP TABLE t1;
#
# Bug#46454: MySQL wrong index optimisation leads to incorrect result & crashes
#
CREATE TABLE t1 (
a INT,
b INT NOT NULL,
c char(100),
KEY (b, c),
KEY (b, a, c)
)
DEFAULT CHARSET = utf8;
INSERT INTO t1 VALUES
(1, 1, 1),
(2, 2, 2),
(3, 3, 3),
(4, 4, 4),
(5, 5, 5),
(6, 6, 6),
(7, 7, 7),
(8, 8, 8),
(9, 9, 9);
INSERT INTO t1 SELECT a + 10, b, c FROM t1;
INSERT INTO t1 SELECT a + 20, b, c FROM t1;
INSERT INTO t1 SELECT a + 40, b, c FROM t1;
INSERT INTO t1 SELECT a + 80, b, c FROM t1;
INSERT INTO t1 SELECT a + 160, b, c FROM t1;
INSERT INTO t1 SELECT a + 320, b, c FROM t1;
INSERT INTO t1 SELECT a + 640, b, c FROM t1;
INSERT INTO t1 SELECT a + 1280, b, c FROM t1 LIMIT 80;
EXPLAIN
SELECT a FROM t1 WHERE b = 1 ORDER BY c DESC LIMIT 9;
SELECT a FROM t1 WHERE b = 1 ORDER BY c DESC LIMIT 9;
EXPLAIN
SELECT DISTINCT a FROM t1 WHERE b = 1 ORDER BY c DESC LIMIT 0, 9;
SELECT DISTINCT a FROM t1 WHERE b = 1 ORDER BY c DESC LIMIT 0, 9;
DROP TABLE t1;

25
sql/sql_select.cc
View File

@ -6151,7 +6151,7 @@ make_join_select(JOIN *join,SQL_SELECT *select,COND *cond)
}
}
if (tmp || !cond)
if (tmp || !cond || tab->type == JT_REF)
{
DBUG_EXECUTE("where",print_where(tmp,tab->table->alias, QT_ORDINARY););
SQL_SELECT *sel= tab->select= ((SQL_SELECT*)
@ -6165,7 +6165,7 @@ make_join_select(JOIN *join,SQL_SELECT *select,COND *cond)
The guard will turn the predicate on only after
the first match for outer tables is encountered.
*/
if (cond)
if (cond && tmp)
{
/*
Because of QUICK_GROUP_MIN_MAX_SELECT there may be a select without
@ -12946,6 +12946,8 @@ find_field_in_item_list (Field *field, void *data)
The index must cover all fields in <order>, or it will not be considered.
@param no_changes No changes will be made to the query plan.
@todo
- sergeyp: Results of all index merge selects actually are ordered
by clustered PK values.
@ -13280,6 +13282,15 @@ test_if_skip_sort_order(JOIN_TAB *tab,ORDER *order,ha_rows select_limit,
}
if (!no_changes)
{
/*
If ref_key used index tree reading only ('Using index' in EXPLAIN),
and best_key doesn't, then revert the decision.
*/
if (!table->covering_keys.is_set(best_key) && table->key_read)
{
table->key_read= 0;
table->file->extra(HA_EXTRA_NO_KEYREAD);
}
if (!quick_created)
{
tab->index= best_key;
@ -13296,16 +13307,6 @@ test_if_skip_sort_order(JOIN_TAB *tab,ORDER *order,ha_rows select_limit,
table->key_read=1;
table->file->extra(HA_EXTRA_KEYREAD);
}
else if (table->key_read)
{
/*
Clear the covering key read flags that might have been
previously set for some key other than the current best_key.
*/
table->key_read= 0;
table->file->extra(HA_EXTRA_NO_KEYREAD);
}
table->file->ha_index_or_rnd_end();
if (join->select_options & SELECT_DESCRIBE)
{

8
sql/table.h
View File

@ -755,7 +755,13 @@ struct st_table {
*/
my_bool force_index;
my_bool distinct,const_table,no_rows;
my_bool key_read, no_keyread;
/**
If set, the optimizer has found that row retrieval should access index
tree only.
*/
my_bool key_read;
my_bool no_keyread;
/*
Placeholder for an open table which prevents other connections
from taking name-locks on this table. Typically used with