two tests still fail:
main.innodb_icp and main.range_vs_index_merge_innodb
call records_in_range() with both range ends being open
(which triggers an assert)
- Correct the way SHOW EXPLAIN code calculates 'need_order' parameter
for JOIN::print_explain().
The calculation is still an approximation (see MDEV entry for details) (even EXPLAIN itself
is wrong in certain cases), but now it's a better approximation than before.
- Make SHOW EXPLAIN code take into account that st_select_lex object without joins can be
a full-featured SELECTs which were already executed and cleaned up.
- Fixed code that was not ready for a major version number > 9
- Fixed test cases that assumed max major version number could be 9
Updated version number for depricated options (will be removed in a later commit)
VERSION:
Version number 10.0.0
client/mysqlbinlog.cc:
Added support for major version numbers > 9
cmake/mysql_version.cmake:
Added support for version numbers that is 0
mysql-test/r/comments.result:
Modified test to handle version number 100000
mysql-test/r/func_system.result:
Modified test to handle version number 100000
mysql-test/r/log_state.result:
Updated depricated error message
mysql-test/r/sp.result:
Modified test to handle version number 100000
mysql-test/r/subselect4.result:
Updated depricated error message
mysql-test/r/variables.result:
Updated depricated error message
mysql-test/suite/rpl/r/rpl_conditional_comments.result:
Modified test to handle version number 100000
mysql-test/suite/rpl/r/rpl_loaddatalocal.result:
Modified test to handle version number 100000
mysql-test/suite/rpl/t/rpl_conditional_comments.test:
Modified test to handle version number 100000
mysql-test/suite/rpl/t/rpl_loaddatalocal.test:
Modified test to handle version number 100000
mysql-test/suite/sys_vars/r/debug_basic.result:
Updated depricated error message
mysql-test/suite/sys_vars/r/engine_condition_pushdown_basic.result:
Updated depricated error message
mysql-test/suite/sys_vars/r/log_basic.result:
Updated depricated error message
mysql-test/suite/sys_vars/r/log_slow_queries_basic.result:
Updated depricated error message
mysql-test/suite/sys_vars/r/multi_range_count_basic.result:
Updated depricated error message
mysql-test/suite/sys_vars/r/rpl_recovery_rank_basic.result:
Updated depricated error message
mysql-test/suite/sys_vars/r/sql_big_selects_func.result:
Updated depricated error message
mysql-test/suite/sys_vars/r/sql_max_join_size_basic.result:
Updated depricated error message
mysql-test/suite/sys_vars/r/sql_max_join_size_func.result:
Updated depricated error message
mysql-test/t/comments.test:
Modified test to handle version number 100000
mysql-test/t/file_contents.test:
Modified test to handle version number 100000
mysql-test/t/func_system.test:
Modified test to handle version number 100000
mysql-test/t/parser_not_embedded.test:
Modified test to handle version number 100000
mysql-test/t/sp.test:
Modified test to handle version number 100000
sql/mysqld.cc:
Updated version number for depricated options (will be removed in a later commit)
sql/slave.cc:
Modified test to handle version number 100000
Better error messages
sql/sql_lex.cc:
Modified test to handle version number 100000 in comment syntax
sql/sys_vars.cc:
Updated version number for depricated options (will be removed in a later commit)
Analysis:
The fix for lp:944706 introduces early subquery optimization.
While a subquery is being optimized some of its predicates may be
removed. In the test case, the EXISTS subquery is constant, and is
evaluated to TRUE. As a result the whole OR is TRUE, and thus the
correlated condition "b = alias1.b" is optimized away. The subquery
becomes non-correlated.
The subquery cache is designed to work only for correlated subqueries.
If constant subquery optimization is disallowed, then the constant
subquery is not evaluated, the subquery remains correlated, and its
execution is cached. As a result execution is fast.
However, when the constant subquery was optimized away, it was neither
cached by the subquery cache, nor it was cached by the internal subquery
caching. The latter was due to the fact that the subquery still appeared
as correlated to the subselect_XYZ_engine::exec methods, and they
re-executed the subquery on each call to Item_subselect::exec.
Solution:
The solution is to update the correlated status of the subquery after it has
been optimized. This status consists of:
- st_select_lex::is_correlated
- Item_subselect::is_correlated
- SELECT_LEX::uncacheable
- SELECT_LEX_UNIT::uncacheable
The status is updated by st_select_lex::update_correlated_cache(), and its
caller st_select_lex::optimize_unflattened_subqueries. The solution relies
on the fact that the optimizer already called
st_select_lex::update_used_tables() for each subquery. This allows to
efficiently update the correlated status of each subquery without walking
the whole subquery tree.
Notice that his patch is an improvement over MySQL 5.6 and older, where
subqueries are not pre-optimized, and the above analysis is not possible.
The patch enables back constant subquery execution during
query optimization after it was disabled during the development
of MWL#89 (cost-based choice of IN-TO-EXISTS vs MATERIALIZATION).
The main idea is that constant subqueries are allowed to be executed
during optimization if their execution is not expensive.
The approach is as follows:
- Constant subqueries are recursively optimized in the beginning of
JOIN::optimize of the outer query. This is done by the new method
JOIN::optimize_constant_subqueries(). This is done so that the cost
of executing these queries can be estimated.
- Optimization of the outer query proceeds normally. During this phase
the optimizer may request execution of non-expensive constant subqueries.
Each place where the optimizer may potentially execute an expensive
expression is guarded with the predicate Item::is_expensive().
- The implementation of Item_subselect::is_expensive has been extended
to use the number of examined rows (estimated by the optimizer) as a
way to determine whether the subquery is expensive or not.
- The new system variable "expensive_subquery_limit" controls how many
examined rows are considered to be not expensive. The default is 100.
In addition, multiple changes were needed to make this solution work
in the light of the changes made by MWL#89. These changes were needed
to fix various crashes and wrong results, and legacy bugs discovered
during development.
- It turns out, there is a case where the join is degenerate, but
join->table_count!= && join->tables_list!=NULL. Need to also check
if join->zero_result_cause!=NULL, too.
- There is a slight problem: The code sets
zero_result_cause= "no matching row in const table"
when NOT running EXPLAIN. The result is that SHOW EXPLAIN will show this line while
regular EXPLAIN will not.
Make SHOW EXPLAIN work for queries that do "Using temporary" and/or "Using filesort"
- Patch#1: Don't lose "Using temporary/filesort" in the SHOW EXPLAIN output.
Analysis:
The reason for the wrong result is the interaction between constant
optimization (in this case 1-row table) and subquery optimization.
- First the outer query is optimized, and 'make_join_statistics' finds that
table t2 has one row, reads that row, and marks the whole table as constant.
This also means that all fields of t2 are constant.
- Next, we optimize the subquery in the end of the outer 'make_join_statistics'.
The field 'f2' is considered constant, with value '3'. The subquery predicate
is rewritten as the constant TRUE.
- The outer query execution detects early that the whole query result is empty
and calls 'return_zero_rows'. Since the query is with implicit grouping, we
have to produce one row with special values for the aggregates (depending on
each aggregate function), and NULL values for all non-aggregate fields. This
function calls 'no_rows_in_result' to set each aggregate function to the
default value when it aggregates over an empty result, and then calls
'send_data', which in turn evaluates each Item in the SELECT list.
- When evaluation reaches the subquery predicate, it executes the subquery
with field 'f2' having a constant value '3', and the subquery produces the
incorrect result '7'.
Solution:
Implement Item::no_rows_in_result for all subquery predicates. In order to
make this work, it is also needed to make all val_* methods of all subquery
predicates respect the Item_subselect::forced_const flag. Otherwise subqueries
are executed anyways, and override the default value set by no_rows_in_result
with whatever result is produced from the subquery evaluation.
Description: When the table has more than one unique or primary key,
INSERT... ON DUP KEY UPDATE statement is sensitive to the order in which
the storage engines checks the keys. Depending on this order, the storage
engine may determine different rows to mysql, and hence mysql can update
different rows on master and slave.
Solution: We mark INSERT...ON DUP KEY UPDATE on a table with more than on unique
key as unsafe therefore the event will be logged in row format if it is available
(ROW/MIXED). If only STATEMENT format is available, a warning will be thrown.
mysql-test/suite/binlog/r/binlog_unsafe.result:
Updated result file
mysql-test/suite/binlog/t/binlog_unsafe.test:
Added test to check for warning being thrown when the unsafe statement is executed
mysql-test/suite/rpl/r/rpl_known_bugs_detection.result:
Updated result file
sql/share/errmsg-utf8.txt:
Added new warning message
sql/sql_base.cc:
check for tables in the query with more than one UNIQUE KEY and INSERT ON DUPLICATE KEY UPDATE, and mark such statements unsafe.
Description: When the table has more than one unique or primary key,
INSERT... ON DUP KEY UPDATE statement is sensitive to the order in which
the storage engines checks the keys. Depending on this order, the storage
engine may determine different rows to mysql, and hence mysql can update
different rows on master and slave.
Solution: We mark INSERT...ON DUP KEY UPDATE on a table with more than on unique
key as unsafe therefore the event will be logged in row format if it is available
(ROW/MIXED). If only STATEMENT format is available, a warning will be thrown.
Background:
- as described in MySQL Internals Prepared Stored
(http://forge.mysql.com/wiki/MySQL_Internals_Prepared_Stored),
the Optimizer sometimes does destructive changes to the parsed
LEX-object (Item-tree), which makes it impossible to re-use
that tree for PS/SP re-execution.
- in order to be able to re-use the Item-tree, the destructive
changes are remembered and rolled back after the statement execution.
The problem, discovered by this bug, was that the objects representing
GROUP-BY clause did not restored after query execution. So, the GROUP-BY
part of the statement could not be properly re-initialized for re-execution
after destructive changes.
Those objects do not take part in the Item-tree, so they can not be saved
using the approach for Item-tree.
The fix is as follows:
- introduce a new array in st_select_lex to store the original
ORDER pointers, representing the GROUP-BY clause;
- Initialize this array in fix_prepare_information().
- restore the list of GROUP-BY items in reinit_stmt_before_use().
Background:
- as described in MySQL Internals Prepared Stored
(http://forge.mysql.com/wiki/MySQL_Internals_Prepared_Stored),
the Optimizer sometimes does destructive changes to the parsed
LEX-object (Item-tree), which makes it impossible to re-use
that tree for PS/SP re-execution.
- in order to be able to re-use the Item-tree, the destructive
changes are remembered and rolled back after the statement execution.
The problem, discovered by this bug, was that the objects representing
GROUP-BY clause did not restored after query execution. So, the GROUP-BY
part of the statement could not be properly re-initialized for re-execution
after destructive changes.
Those objects do not take part in the Item-tree, so they can not be saved
using the approach for Item-tree.
The fix is as follows:
- introduce a new array in st_select_lex to store the original
ORDER pointers, representing the GROUP-BY clause;
- Initialize this array in fix_prepare_information().
- restore the list of GROUP-BY items in reinit_stmt_before_use().
mysql-test/suite/innodb/t/group_commit_crash.test:
remove autoincrement to avoid rbr being used for insert ... select
mysql-test/suite/innodb/t/group_commit_crash_no_optimize_thread.test:
remove autoincrement to avoid rbr being used for insert ... select
mysys/my_addr_resolve.c:
a pointer to a buffer is returned to the caller -> the buffer cannot be on the stack
mysys/stacktrace.c:
my_vsnprintf() is ok here, in 5.5
https://mariadb.atlassian.net/browse/MDEV-28
This task implements a new clause LIMIT ROWS EXAMINED <num>
as an extention to the ANSI LIMIT clause. This extension
allows to limit the number of rows and/or keys a query
would access (read and/or write) during query execution.
