Now partition engine adds underlying tables to the QC and ask underlying tables engine permittion to cache the query and return result of the query.
Incorrect QC cleanup in case of table registration failure fixe.
Unified interface for myisammrg & partitioned engnes for QC.
make sure that find_date_time_item() is called before agg_arg_charsets_for_comparison().
optimize Item_func_conv_charset to avoid conversion if no string result is needed
Analysis:
The fix for bug lp:985667 implements the method Item_subselect::no_rows_in_result()
for all main kinds of subqueries. The purpose of this method is to be called from
return_zero_rows() and set Items to some default value in the case when a query
returns no rows. Aggregates and subqueries require special treatment in this case.
Every implementation of Item_subselect::no_rows_in_result() called
Item_subselect::make_const() to set the subquery predicate to its default value
irrespective of where the predicate was located in the query. Once the predicate
was set to a constant it was never executed.
At the same time, the JOIN object of the fake select for UNIONs (the one used for
the final result of the UNION), was set after all subqueries in the union were
executed. Since we set the subquery as constant, it was never executed, and the
corresponding JOIN was never created.
In order to decide whether the result of NOT IN is NULL or FALSE, Item_in_optimizer
needs to check if the subquery result was empty or not. This is where we got the
crash, because subselect_union_engine::no_rows() checks for
unit->fake_select_lex->join->send_records, and the join object was NULL.
Solution:
If a subquery is in the HAVING clause it must be evaluated in order to know its
result, so that we can properly filter the result records. Once subqueries in the
HAVING clause are executed even in the case of no result rows, this specific
crash will be solved, because the UNION will be executed, and its JOIN will be
constructed. Therefore the fix for this crash is to narrow the fix for lp:985667,
and to apply Item_subselect::no_rows_in_result() only when the subquery predicate
is in the SELECT clause.
The class Item_func missed an implementation of the virtual
function update_null_value.
Back-ported the fix for bug 62125 from mysql 5.6 code line.
The test case was also back-ported.
Analysis:
Queries with implicit grouping (there is aggregate, but no group by)
follow some non-obvious semantics in the case of empty result set.
Aggregate functions produce some special "natural" value depending on
the function. For instance MIN/MAX return NULL, COUNT returns 0.
The complexity comes from non-aggregate expressions in the select list.
If the non-aggregate expression is a constant, it can be computed, so
we should return its value, however if the expression is non-constant,
and depends on columns from the empty result set, then the only meaningful
value is NULL.
The cause of the wrong result was that for subqueries the optimizer didn't
make a difference between constant and non-constant ones in the case of
empty result for implicit grouping.
Solution:
In all implementations of Item_subselect::no_rows_in_result() check if the
subquery predicate is constant. If it is constant, do not set it to the
default value for implicit grouping, instead let it be evaluated.
The bug prevented acceptance of UNION queries whose non-first select
clauses contained join expressions with degenerated single-table nests
as valid queries.
The bug was introduced into mysql-5.5 code line by the patch for
bug 33204.
Fixed MDEV-331: last_insert_id() returns a signed number
mysql-test/r/auto_increment.result:
Added test case
mysql-test/t/auto_increment.test:
Added test case
sql/item_func.h:
Changed last_insert_id() to be unsigned.
Analysis:
When the method JOIN::choose_subquery_plan() decided to apply
the IN-TO-EXISTS strategy, it set the unit and select_lex
uncacheable flag to UNCACHEABLE_DEPENDENT_INJECTED unconditionally.
As result, even if IN-TO-EXISTS injected non-correlated predicates,
the subquery was still treated as correlated.
Solution:
Set the subquery as correlated only if the injected predicate(s) depend
on the outer query.
backport dmitry.shulga@oracle.com-20120209125742-w7hdxv0103ymb8ko from mysql-trunk:
Patch for bug#11764747 (formerly known as 57612): SET GLOBAL READ_ONLY=1 cannot
progress when a table is locked with LOCK TABLES.
The reason for the bug was that mysql server makes a flush of all open tables
during handling of statement 'SET GLOBAL READ_ONLY=1'. Therefore if some of
these tables were locked by "LOCK TABLE ... READ" from a different connection,
then execution of statement 'SET GLOBAL READ_ONLY=1' would be waiting for
the lock for such table even if the table was locked in a compatible read mode.
Flushing of all open tables before setting of read_only system variable
is inherited from 5.1 implementation since this was the only possible approach
to ensure that there isn't any pending write operations on open tables.
Start from version 5.5 and above such behaviour is guaranteed by the fact
that we acquire global_read_lock before setting read_only flag. Since
acquiring of global_read_lock is successful only when there isn't any
active write operation then we can remove flushing of open tables from
processing of SET GLOBAL READ_ONLY=1.
This modification changes the server behavior so that read locks held
by other connections (LOCK TABLE ... READ) no longer will block attempts
to enable read_only.
Analysis:
The crash is a result of Item_cache_temporal::example not being set
(it is NULL). It turns out that the value of Item_cache_temporal
may be set directly by calling Item_cache_temporal::store_packed
without ever setting the "example" of this Item_cache. Therefore
the failing assertion is too narrow.
Solution:
Remove the assert.
In principle we could overwrite this method for Item_cache_temporal,
but it doesn't make sense just for this assert.
CHEAP SQ: Valgrind warnings "Memory lost" with IN and EXISTS nested subquery, materialization+semijoin
Analysis:
The memory leak was a result of the interaction of semi-join optimization
with early optimization of constant subqueries. The function:
setup_jtbm_semi_joins() created a dummy temporary table "dummy_table"
in order to make some JOIN_TAB objects complete. Normally, such temporary
tables are freed inside JOIN_TAB::cleanup.
However, the inner-most subquery is pre-optimized, which allows the
optimization fo the MAX subquery to determine that its WHERE is TRUE,
and thus to compute the result of the MAX during optimization. This
ultimately allows the optimize phase of the outer query to find that
it WHERE clause is FALSE. Once JOIN::optimize finds that the result
set is empty, it sets zero_result_cause, and returns *before* it ever
reached make_join_statistics(). As a result the query plan has no
JOIN_TABs at all. Since the temporary table is supposed to be cleanup
via JOIN_TAB::cleanup, this never happens because there is no JOIN_TAB
for this table. Hence we get a memory leak.
Solution:
Whenever there are no JOIN_TABs, iterate over all table reference in
JOIN::join_list, and free the ones that contain semi-join temporary
tables.
Analysis:
When a subquery that needs a temp table is executed during
the prepare or optimize phase of the outer query, at the end
of the subquery execution all the JOIN_TABs of the subquery
are replaced by a new JOIN_TAB that selects from the temp table.
However that temp table has no corresponding TABLE_LIST.
Once EXPLAIN execution reaches its last phase, it tries to print
the names of the subquery tables through its TABLE_LISTs, but in
the case of this bug there is no such TABLE_LIST (it is NULL),
hence a crash.
Solution:
The fix is to block subquery evaluation inside
Item_func_like::fix_fields and Item_func_like::select_optimize()
using the Item::is_expensive() test.
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.
- In JOIN::exec(), make the having->update_used_tables() call before we've
made the JOIN::cleanup(full=true) call. The latter frees SJ-Materialization
structures, which correlated subquery predicate items attempt to walk afterwards.
Analysis:
The problem in the original MySQL bug is that the range optimizer
performs its analysis in a separate MEM_ROOT object that is freed
after the range optimzier is done. During range analysis get_mm_tree
calls Item_func_like::select_optimize, which in turn evaluates its
right argument. In the test case the right argument is a subquery.
In MySQL, subqueries are optimized lazyly, thus the call to val_str
triggers optimization for the subquery. All objects needed by the
subquery plan end up in the temporary MEM_ROOT used by the range
optimizer. When execution ends, the JOIN::cleanup process tries to
cleanup objects of the subquery plan, but all these objects are gone
with the temporary MEM_ROOT. The solution for MySQL is to switch the
mem_root.
In MariaDB with the patch for bug lp:944706, all constant subqueries
that may be used by the optimization process are preoptimized. Therefore
Item_func_like::select_optimize only triggers subquery execution, and
the above problem is not present.
The patch however adds a test whether the evaluated right argument of
the LIKE predicate is expensive. This is consistent with our approach
not to evaluate expensive expressions during optimization.
This is a backport of the (unchaged) fix for MySQL bug #11764372, 57197.
Analysis:
When the outer query finishes its main execution and computes GROUP BY,
it needs to construct a new temporary table (and a corresponding JOIN) to
execute the last DISTINCT operation. At this point JOIN::exec calls
JOIN::join_free, which calls JOIN::cleanup -> TMP_TABLE_PARAM::cleanup
for both the outer and the inner JOINs. The call to the inner
TMP_TABLE_PARAM::cleanup sets copy_field = NULL, but not copy_field_end.
The final execution phase that computes the DISTINCT invokes:
evaluate_join_record -> end_write -> copy_funcs
The last function copies the results of all functions into the temp table.
copy_funcs walks over all functions in join->tmp_table_param.items_to_copy.
In this case items_to_copy contains both assignments to user variables.
The process of copying user variables invokes Item_func_set_user_var::check
which in turn re-evaluates the arguments of the user variable assignment.
This in turn triggers re-evaluation of the subquery, and ultimately
copy_field.
However, the previous call to TMP_TABLE_PARAM::cleanup for the subquery
already set copy_field to NULL but not its copy_field_end. This results
in a null pointer access, and a crash.
Fix:
Set copy_field_end and save_copy_field_end to null when deleting
copy fields in TMP_TABLE_PARAM::cleanup().
Analysis:
The optimizer detects an empty result through constant table optimization.
Then it calls return_zero_rows(), which in turns calls inderctly
Item_maxmin_subselect::no_rows_in_result(). The latter method set "value=0",
however "value" is pointer to Item_cache, and not just an integer value.
All of the Item_[maxmin | singlerow]_subselect::val_XXX methods does:
if (forced_const)
return value->val_real();
which of course crashes when value is a NULL pointer.
Solution:
When the optimizer discovers an empty result set, set
Item_singlerow_subselect::value to a FALSE constant Item instead of NULL.
Handle the 'set read_only=1' in lighter way, than the FLUSH TABLES READ LOCK;
For the transactional engines we don't wait for operations on that tables to finish.
per-file comments:
mysql-test/r/read_only_innodb.result
MDEV-136 Non-blocking "set read_only".
test result updated.
mysql-test/t/read_only_innodb.test
MDEV-136 Non-blocking "set read_only".
test case added.
sql/mysql_priv.h
MDEV-136 Non-blocking "set read_only".
The close_cached_tables_set_readonly() declared.
sql/set_var.cc
MDEV-136 Non-blocking "set read_only".
Call close_cached_tables_set_readonly() for the read_only::set_var.
sql/sql_base.cc
MDEV-136 Non-blocking "set read_only".
Parameters added to the close_cached_tables implementation,
close_cached_tables_set_readonly declared.
Prevent blocking on the transactional tables if the
set_readonly_mode is on.
- make make_cond_after_sjm() correctly handle OR clauses where one branch refers to the semi-join table
while the other branch refers to the non-semijoin table.
The cause for this bug is that the method JOIN::get_examined_rows iterates over all
JOIN_TABs of the join assuming they are just a sequence. In the query above, the
innermost subquery is merged into its parent query. When we call
JOIN::get_examined_rows for the second-level subquery, the iteration that
assumes sequential order of join tabs goes outside the join_tab array and calls
the method JOIN_TAB::get_examined_rows on uninitialized memory.
The fix is to iterate over JOIN_TABs in a way that takes into account the nested
semi-join structure of JOIN_TABs. In particular iterate as select_describe.
