Analysis:
In the test query semi-join merges the inner-most subquery
into the outer subquery, and the optimization of the merged
subquery finds some new index access methods. Later the
IN-EXISTS transformation is applied to the unmerged subquery.
Since the optimizer is instructed to not consider
materialization, it reoptimizes the plan in-place to take into
account the new IN-EXISTS conditions. Just before reoptimization
JOIN::choose_subquery_plan resets the query plan, which also
resets the access methods found during the semi-join merge.
Then reoptimization discovers there are no new access methods,
but it leaves the query plan in its reset state. Later semi-join
crashes because it assumes these access methods are present.
Solution:
When reoptimizing in-place, reset the query plan only after new
access methods were discovered. If no new access methods were
discovered, leave the current plan as it was.
Added more printing of errors to myisamchk.
mysys/mf_iocache.c:
Write error message if failed seek.
sql/table.cc:
Fixed buffer overflow bug:
- It's not enough to check for mysql_version to to detect partion indicator as the version may have been updated by mysql_upgrade.
storage/myisam/ha_myisam.cc:
Don't log same error twice.
Don't reset log_all_errors if it's set
storage/myisam/mi_check.c:
Fixed bug that caused repair() to not report error if called twice (as when doing retry)
More printing of errors.
storage/myisam/sort.c:
Set my_errno in case of out of memory errors.
sql/mysqld.cc:
Log errors if thd->log_all_errors is set
sql/sql_class.cc:
Add log_all_errors
sql/sql_class.h:
Add log_all_errors
storage/myisam/ha_myisam.cc:
Write db and table name for all logged errors
Log errors also during auto_recovery
During auto_recovery, set thd->log_all_errors if log_warnings >2 to ensure that system errors are also logged to file
- The problem was that the code that made the check whether the subquery is an AND-part of the WHERE
clause didn't work correctly for nested subqueries. In particular, grand-child subquery in HAVING was
treated as if it was in the WHERE, which eventually caused an assert when replace_where_subcondition
looked for the subquery predicate in the WHERE and couldn't find it there.
- The fix: Removed implementation of "thd_marker approach". thd->thd_marker was used to determine the
location of subquery predicate: setup_conds() would set accordingly it when making the
{where|on_expr}->fix_fields(...)
call so that AND-parts of the WHERE/ON clauses can determine they are the AND-parts.
Item_cond_or::fix_fields(), Item_func::fix_fields(), Item_subselect::fix_fields (this one was missed),
and all other items-that-contain-items had to reset thd->thd_marker before calling fix_fields() for
their children items, so that the children can see they are not AND-parts of WHERE/ON.
- The "thd_marker approach" required that a lot of code in different locations maintains correct value of
thd->thd_marker, so it was replaced with:
- The new approach with mark_as_condition_AND_part does not keep context in thd->thd_marker. Instead,
setup_conds() now calls
{where|on_expr}->mark_as_condition_AND_part()
and implementations of that function make sure that:
- parts of AND-expressions get the mark_as_condition_AND_part() call
- Item_in_subselect objects record that they are AND-parts of WHERE/ON
Analysis:
Constant table optimization of the outer query finds that
the right side of the equality is a constant that can
be used for an eq_ref access to fetch one row from t1,
and substitute t1 with a constant. Thus constant optimization
triggers evaluation of the subquery during the optimize
phase of the outer query.
The innermost subquery requires a plan with a temporary
table because with InnoDB tables the exact count of rows
is not known, and the empty tables cannot be optimzied
way. JOIN::exec for the innermost subquery substitutes
the subquery tables with a temporary table.
When EXPLAIN gets to print the tables in the innermost
subquery, EXPLAIN needs to print the name of each table
through the corresponding TABLE_LIST object. However,
the temporary table created during execution doesn't
have a corresponding TABLE_LIST, so we get a null
pointer exception.
Solution:
The solution is to forbid using expensive constant
expressions for eq_ref access for contant table
optimization. Notice that eq_ref with a subquery
providing the value is still possible during regular
execution.
Analysis:
During the first execution of the query through the stored
procedure, the optimization phase calls
substitute_for_best_equal_field(), which calls
Item_in_optimizer::transform(). The latter replaces
Item_in_subselect::left_expr with args[0] via assignment.
In this test case args[0] is an Item_outer_ref which is
created/deallocated for each re-execution. As a result,
during the second execution Item_in_subselect::left_expr
pointed to freed memory, which resulted in a crash.
Solution:
The solution is to use change_item_tree(), so that the
origianal left expression is restored after each execution.
Analysis:
Partial matching is used even when there are no NULLs in
a materialized subquery, as long as the left NOT IN operand
may contain NULL values.
This case was not handled correctly in two different places.
First, the implementation of parital matching did not clear
the set of matching columns when the merge process advanced
to the next row.
Second, there is no need to perform partial matching at all
when the left operand has no NULLs.
Solution:
First fix subselect_rowid_merge_engine::partial_match() to
properly cleanup the bitmap of matching keys when advancing
to the next row.
Second, change subselect_partial_match_engine::exec() so
that when the materialized subquery doesn't contain any
NULLs, and the left operand of [NOT] IN doesn't contain
NULLs either, the method returns without doing any
unnecessary partial matching. The correct result in this
case is in Item::in_value.
When the WHERE/HAVING condition of a subquery has been transformed
by the optimizer the pointer stored the 'where'/'having' field
of the SELECT_LEX structure used for the subquery must be updated
accordingly. Otherwise the pointer may refer to an invalid item.
This can lead to the reported assertion failure for some queries
with correlated subqueries
The bug is a duplicate of MySQL's Bug#11764086,
however MySQL's fix is incomplete for MariaDB, so
this fix is slightly different.
In addition, this patch renames
Item_func_not_all::top_level() to is_top_level_item()
to make it in line with the analogous methods of
Item_in_optimizer, and Item_subselect.
Analysis:
It is possible to determine whether a predicate is
NULL-rejecting only if it is a top-level one. However,
this was not taken into account for Item_in_optimizer.
As a result, a NOT IN predicate was erroneously
considered as NULL-rejecting, and the NULL-complemented
rows generated by the outer join were rejected before
being checked by the NOT IN predicate.
Solution:
Change Item_in_optimizer to be considered as
NULL-rejecting only if it a top-level predicate.
opt_range.cc: modified print_key() so that it doesn't do memory re-allocs when
printing multipart keys over varchar columns. When it did, key printout in
debug trace was interrupted with my_malloc/free printouts.
- add_ref_to_table_cond() should not just overwrite pre_idx_push_select_cond
with the contents tab->select_cond.
pre_idx_push_select_cond exists precisely for the reason that it may contain
a condition that is a strict superset of what is in tab->select_cond.
The fix is to inject generated equality into pre_idx_push_select_cond.
- Make simplify_joins() set maybe_null=FALSE for tables that were on the
inner sides of inner joins and then were moved to the inner sides of semi-joins.
thd->user_connect is now handled in thd->clenup() which will ensure that it works in all context (including slaves).
I added also some DBUG_ASSERT() to ensure that things are working correctly.
sql/sql_acl.cc:
Reset thd->user_connect on failed check_for_max_user_connections() to ensure we don't decrement value twice.
Removed not needed call to decrease_user_connections() as thd->cleanup() will now do it.
sql/sql_class.cc:
Call decrease_user_connections() in thd->cleanup()
sql/sql_connect.cc:
Ensure we don't allocate thd->user_connect twice.
Simplify check_for_max_user_connections().
sql/sql_parse.cc:
Ensure that thd->user_connect is handled properly in for 'change_user' command.
When merging a view / derived table the function SELECT_LEX::merge_subquery
incorrectly updated the list SELECT_LEX::leaf_tables. Erroneously it
appended the leaf_tables list of the merged object L and then removed the
reference to the merged object T from the SELECT_LEX::leaf_tables list.
A correct implementation should insert the list L into the
SELECT_LEX::leaf_tables list in place of the element of the list that
refers to T.
The bug could lead to wrong results or even crashes for queries with
nested outer joins over views / derived tables.
sql/sql_expression_cache.cc:
Early check of subquery cache hit rate added to limit its performance impact in the worst case.
Disabling cache moved to method.
sql/sql_expression_cache.h:
Disabling cache moved to method.
The method Item_ref::not_null_tables() returned incorrect bitmap
for outer references to view columns. This could cause an invalid
conversion of an outer join into an inner join that could lead
to a wrong result set for a query with a correlated subquery over
an outer join whose where condition had an outer reference to a view.
The method Item_func_isnull::update_used_tables() erroneously did not
update cached values stored in the fields used_tables_cache and
const_item_cache of the Item_func_isnull objects. As a result the
Item_func_isnull::used_tables() returned wrong bitmaps and, as a
consequence, push-down predicates could be attached to wrong tables.
This bug is a special case of lp:813447.
Analysis:
Constant optimization finds that the condition t2.a = 1
can be used to access the primary key of table 't2'. As
a result both outer table t1,t2 are considered as constant
when we reach the execution phase. At the same time, during
constant optimization, the IN predicate is not evaluated
because it is expensive.
When execution of the outer query reaches do_select(),
control flow enter the branch:
if (join->table_count == join->const_tables)
{ ... }
This branch checks only the WHERE and HAVING clauses,
but doesn't check the ON clauses of the query. Since the
IN predicate was not evaluated during optimization, it is
not evaluated at all, thus execution doesn't detect that
the ON clause is FALSE.
Solution:
Similar to the patch for bug lp:813447, exclude system
tables from constant substitution based on unique key
lookups if there is an expensive ON condition on the
inner table.
- create_ref_for_key() has the code that walks KEYUSE array and tries to use
maximum number of keyparts for ref (and eq_ref and ref_or_null) access.
When one constructs ref access for table that is inside a SJ-Materialization
nest, it is not possible to use tables that are ouside the nest (because
materialization is performed before they have any "current value").
The bug was caused by this function not taking this into account.
revno: 2876.47.174
revision-id: jorgen.loland@oracle.com-20110519120355-qn7eprkad9jqwu5j
parent: mayank.prasad@oracle.com-20110518143645-bdxv4udzrmqsjmhq
committer: Jorgen Loland <jorgen.loland@oracle.com>
branch nick: mysql-trunk-11765831
timestamp: Thu 2011-05-19 14:03:55 +0200
message:
BUG#11765831: 'RANGE ACCESS' MAY INCORRECTLY FILTER
AWAY QUALIFYING ROWS
The problem was that the ranges created when OR'ing two
conditions could be incorrect. Without the bugfix,
"I <> 6 OR (I <> 8 AND J = 5)" would create these ranges:
"NULL < I < 6",
"6 <= I <= 6 AND 5 <= J <= 5",
"6 < I < 8",
"8 <= I <= 8 AND 5 <= J <= 5",
"8 < I"
While the correct ranges is
"NULL < I < 6",
"6 <= I <= 6 AND 5 <= J <= 5",
"6 < I"
The problem occurs when key_or() ORs
(1) "NULL < I < 6, 6 <= I <= 6 AND 5 <= J <= 5, 6 < I" with
(2) "8 < I AND 5 <= J <= 5"
The reason for the bug is that in key_or(), SEL_ARG *tmp is
used to point to the range in (1) above that is merged with
(2) while key1 points to the root of the red-black tree of
(1). When merging (1) and (2), tmp refers to the "6 < I"
part whereas the root is the "6 <= ... AND 5 <= J <= 5" part.
key_or() decides that the tmp range needs to be split into
"6 < I < 8, 8 <= I <= 8, 8 < I", in which next_key_part of the
second range should be that of tmp. However, next_key_part is
set to key1->next_key_part ("5 <= J <= 5") instead of
tmp->next_key_part (empty). Fixing this gives the correct but
not optimal ranges:
"NULL < I < 6",
"6 <= I <= 6 AND 5 <= J <= 5",
"6 < I < 8",
"8 <= I <= 8",
"8 < I"
A second problem can be seen above: key_or() may create
adjacent ranges that could be replaced with a single range.
Fixes for this is also included in the patch so that the range
above becomes correct AND optimal:
"NULL < I < 6",
"6 <= I <= 6 AND 5 <= J <= 5",
"6 < I"
Merging adjacent ranges like this gives a slightly lower cost
estimate for the range access.
This problem could be observed for queries with nested outer joins
for which the not_exist optimization were applicable.
The problem was caused by the code of the patch for bug #49322
that erroneously forced the return to the previous nested loop
level when the join algorithm successfully builds a partial record
for an embedded outer to which the not_exist optimization could be
applied.
Actually the immediate return to the previous nested loops level
is correct only if this partial record is rejected by a predicate
pushed down to one of the inner tables of this outer join. Otherwise
attempts to find extensions of this record must be made.
sql/sql_expression_cache.cc:
Do not go on disk if hit rate is not good.
Local hit/miss counters added.
sql/sql_expression_cache.h:
Local hit/miss counters added.
In case of two views with subqueries it is dificult to decide about order of injected ORDER BY clauses.
A simple solution is just prohibit ORDER BY injection if there is other order by.
mysql-test/r/view.result:
New test added, old test changed.
mysql-test/t/view.test:
New test aded.
sql/share/errmsg.txt:
new warning added.
sql/sql_view.cc:
Inject ORDER BY only if there is no other one.
Warning about ignoring ORDER BY in this case for EXPLAIN EXTENDED.
There are 2 volatile condition constructions AND/OR constructions and fields(references) when first
good supported to be top elements of conditions because it is normal practice
(see copy_andor_structure for example) fields without any expression in the condition is really rare
and mostly useless case however it could lead to problems when optimiser changes/moves them unaware
of other variables referring to them. An easy solution of this problem is just to replace single field
in a condition with equivalent expression well supported by the server (<field> -> <field> != 0).
mysql-test/r/view.result:
New test added.
mysql-test/t/view.test:
New test added.
sql/sql_parse.cc:
<field> -> <field> != 0
sql/sql_yacc.yy:
<field> -> <field> != 0
