#At file:///home/rl136806/mysql/repo/mysql-work2/ based on revid:roy.lyseng@stripped
3222 Roy Lyseng 2010-08-04
Bug#51457: Firstmatch semijoin strategy gives wrong results for
certain query plans
When the optimizer selects a semijoin FirstMatch plan that has
non-correlated tables interspersed with inner tables, the "jumps"
are placed so that execution might become incorrect.
Example: A query with an outer correlated table ot, a non-correlated
table nt and two inner tables it1 and it2 are used in a query and the
optimizer chooses the FirstMatch join order ot - it1 - nt - it2.
The optimizer assigns a "jump" from table it2 to ot. This strategy will
omit duplicates resulting from table nt.
The fix assures that the jump from the last table in a consecutive
range of inner table goes to the most immediately preceeding outer
table (regardless of whether the outer table is correlated or not).
In this case, there are two consecutive ranges of inner tables:
{it1} and {it2}. In the first range, the last inner table is it1, the
jump should be to table ot. In the second range, the jump from it2
should be to nt.
It is currently possible to generate such query plans, hence the
bug fix includes some test cases. However, such plans are probably
generated due to a problem with the join optimizer cost model.
When this problem is fixed, it may be impossible to generate
such FirstMatch plans, unless one can assign different costs
to different tables, or another measure is used to force a specific
join order.
mysql-test/r/subselect_innodb.result
Test results for bug#51457.
mysql-test/t/subselect_innodb.test
Test case for bug#51457. Notice the above comment for test validity.
The test goes into subselect_innodb because it is required to use
tables with one row that are not hit by const table optimization.
sql/sql_select.cc
In setup_semijoin_dups_elimination(), in the case for FIRST_MATCH,
loop over the set of inner and non-correlated outer tables and assign
jump target to the last table in each consecutive range of inner
tables. The jump target should be the most immediately preceeding
outer table.
modified:
mysql-test/r/subselect_innodb.result
mysql-test/t/subselect_innodb.test
sql/sql_select.cc
=== modified file 'mysql-test/r/subselect_innodb.result'
--- a/mysql-test/r/subselect_innodb.result 2010-06-19 13:22:14 +0000
+++ b/mysql-test/r/subselect_innodb.result 2010-08-04 07:05:47 +0000
@@ -392,3 +392,86 @@ and t2.a='1' AND t1.a=t3.b) > 0;
a
2
DROP TABLE t1,t2,t3;
+#
+# Bug#51457 Firstmatch semijoin strategy gives wrong results for
+# certain query plans
+#
+SET @@default_storage_engine='innodb';
+SET @@optimizer_switch='semijoin=on,materialization=off,firstmatch=on,loosescan=off';
+SET @@optimizer_join_cache_level=0;
+CREATE TABLE t0(a INTEGER);
+CREATE TABLE t1(a INTEGER);
+INSERT INTO t1 VALUES(1);
+CREATE TABLE t2(a INTEGER);
+INSERT INTO t2 VALUES(5), (8);
+CREATE TABLE t6(a INTEGER);
+INSERT INTO t6 VALUES(7), (1), (0), (5), (1), (4);
+CREATE TABLE t8(a INTEGER);
+INSERT INTO t8 VALUES(1), (3), (5), (7), (9), (7), (3), (1);
+EXPLAIN
+SELECT *
+FROM t2 AS nt2
+WHERE 1 IN (SELECT it1.a
+FROM t1 AS it1 JOIN t6 AS it3 ON it1.a=it3.a);
+id select_type table type possible_keys key key_len ref rows Extra
+1 PRIMARY it1 ALL NULL NULL NULL NULL 1 Using where; FirstMatch
+1 PRIMARY nt2 ALL NULL NULL NULL NULL 2
+1 PRIMARY it3 ALL NULL NULL NULL NULL 6 Using where; FirstMatch(nt2)
+SELECT *
+FROM t2 AS nt2
+WHERE 1 IN (SELECT it1.a
+FROM t1 AS it1 JOIN t6 AS it3 ON it1.a=it3.a);
+a
+5
+8
+EXPLAIN
+SELECT *
+FROM t2 AS nt2, t8 AS nt4
+WHERE 1 IN (SELECT it1.a
+FROM t1 AS it1 JOIN t6 AS it3 ON it1.a=it3.a);
+id select_type table type possible_keys key key_len ref rows Extra
+1 PRIMARY it1 ALL NULL NULL NULL NULL 1 Using where; FirstMatch
+1 PRIMARY nt2 ALL NULL NULL NULL NULL 2
+1 PRIMARY it3 ALL NULL NULL NULL NULL 6 Using where; FirstMatch(nt2)
+1 PRIMARY nt4 ALL NULL NULL NULL NULL 8
+SELECT *
+FROM t2 AS nt2, t8 AS nt4
+WHERE 1 IN (SELECT it1.a
+FROM t1 AS it1 JOIN t6 AS it3 ON it1.a=it3.a);
+a a
+5 1
+5 3
+5 5
+5 7
+5 9
+5 7
+5 3
+5 1
+8 1
+8 3
+8 5
+8 7
+8 9
+8 7
+8 3
+8 1
+EXPLAIN
+SELECT *
+FROM t0 AS ot1, t2 AS nt3
+WHERE ot1.a IN (SELECT it2.a
+FROM t1 AS it2 JOIN t8 AS it4 ON it2.a=it4.a);
+id select_type table type possible_keys key key_len ref rows Extra
+1 PRIMARY ot1 ALL NULL NULL NULL NULL 1
+1 PRIMARY it2 ALL NULL NULL NULL NULL 1 Using where; FirstMatch(ot1)
+1 PRIMARY nt3 ALL NULL NULL NULL NULL 2
+1 PRIMARY it4 ALL NULL NULL NULL NULL 8 Using where; FirstMatch(nt3)
+SELECT *
+FROM t0 as ot1, t2 AS nt3
+WHERE ot1.a IN (SELECT it2.a
+FROM t1 AS it2 JOIN t8 AS it4 ON it2.a=it4.a);
+a a
+DROP TABLE t0, t1, t2, t6, t8;
+SET @@default_storage_engine=default;
+SET @@optimizer_switch=default;
+SET @@optimizer_join_cache_level=default;
+# End of bug#51457
=== modified file 'mysql-test/t/subselect_innodb.test'
--- a/mysql-test/t/subselect_innodb.test 2010-06-18 08:45:53 +0000
+++ b/mysql-test/t/subselect_innodb.test 2010-08-04 07:05:47 +0000
@@ -401,3 +401,67 @@ SELECT t1.* FROM t1 WHERE (SELECT COUNT(
and t2.a='1' AND t1.a=t3.b) > 0;
DROP TABLE t1,t2,t3;
+
+--echo #
+--echo # Bug#51457 Firstmatch semijoin strategy gives wrong results for
+--echo # certain query plans
+--echo #
+
+SET @@default_storage_engine='innodb';
+SET @@optimizer_switch='semijoin=on,materialization=off,firstmatch=on,loosescan=off';
+SET @@optimizer_join_cache_level=0;
+
+CREATE TABLE t0(a INTEGER);
+
+CREATE TABLE t1(a INTEGER);
+INSERT INTO t1 VALUES(1);
+
+CREATE TABLE t2(a INTEGER);
+INSERT INTO t2 VALUES(5), (8);
+
+CREATE TABLE t6(a INTEGER);
+INSERT INTO t6 VALUES(7), (1), (0), (5), (1), (4);
+
+CREATE TABLE t8(a INTEGER);
+INSERT INTO t8 VALUES(1), (3), (5), (7), (9), (7), (3), (1);
+
+EXPLAIN
+SELECT *
+FROM t2 AS nt2
+WHERE 1 IN (SELECT it1.a
+ FROM t1 AS it1 JOIN t6 AS it3 ON it1.a=it3.a);
+
+SELECT *
+FROM t2 AS nt2
+WHERE 1 IN (SELECT it1.a
+ FROM t1 AS it1 JOIN t6 AS it3 ON it1.a=it3.a);
+
+EXPLAIN
+SELECT *
+FROM t2 AS nt2, t8 AS nt4
+WHERE 1 IN (SELECT it1.a
+ FROM t1 AS it1 JOIN t6 AS it3 ON it1.a=it3.a);
+
+SELECT *
+FROM t2 AS nt2, t8 AS nt4
+WHERE 1 IN (SELECT it1.a
+ FROM t1 AS it1 JOIN t6 AS it3 ON it1.a=it3.a);
+
+EXPLAIN
+SELECT *
+FROM t0 AS ot1, t2 AS nt3
+WHERE ot1.a IN (SELECT it2.a
+ FROM t1 AS it2 JOIN t8 AS it4 ON it2.a=it4.a);
+
+SELECT *
+FROM t0 as ot1, t2 AS nt3
+WHERE ot1.a IN (SELECT it2.a
+ FROM t1 AS it2 JOIN t8 AS it4 ON it2.a=it4.a);
+
+DROP TABLE t0, t1, t2, t6, t8;
+
+SET @@default_storage_engine=default;
+SET @@optimizer_switch=default;
+SET @@optimizer_join_cache_level=default;
+
+--echo # End of bug#51457
=== modified file 'sql/sql_select.cc'
--- a/sql/sql_select.cc 2010-07-30 07:32:20 +0000
+++ b/sql/sql_select.cc 2010-08-04 07:05:47 +0000
@@ -1509,9 +1509,26 @@ int setup_semijoin_dups_elimination(JOIN
{
JOIN_TAB *jump_to= tab - 1;
DBUG_ASSERT(tab->emb_sj_nest != NULL); // First table must be inner
- if (!tab->emb_sj_nest)
- jump_to= tab; /// @todo fix this (BUG#51457)
- tab_end->do_firstmatch= jump_to;
+ for (JOIN_TAB *j= tab; j <= tab_end; j++)
+ {
+ if (!j->emb_sj_nest)
+ {
+ /*
+ Let last non-correlated table be jump target for
+ subsequent inner tables.
+ */
+ jump_to= j;
+ }
+ else
+ {
+ /*
+ Assign jump target for last table in a consecutive range of
+ inner tables.
+ */
+ if (j == tab_end || !(j+1)->emb_sj_nest)
+ j->do_firstmatch= jump_to;
+ }
+ }
i+= pos->n_sj_tables;
break;
}
Attachment: [text/bzr-bundle] bzr/roy.lyseng@oracle.com-20100804070547-5hwfhjy0efes4y02.bundle
| Thread |
|---|
| • bzr commit into mysql-next-mr-opt-backporting branch (roy.lyseng:3222)Bug#51457 | Roy Lyseng | 4 Aug |
