Analysis:
The queries in question use the [unique | index]_subquery execution methods.
These methods reuse the ref keys constructed by create_ref_for_key(). The
way create_ref_for_key() works is that it doesn't store in ref.key_copy[]
store_key elements that represent constants. In particular it doesn't store
the store_key for NULL constants.
The execution of [unique | index]_subquery calls
subselect_uniquesubquery_engine::copy_ref_key, which in addition to copy
the left IN argument into a index lookup key, is supposed to detect if
the left IN argument contains NULLs. Since the store_key for the NULL
constant is not copied into the key array, the null is not detected, and
execution erroneously proceeds as if it should look for a complete match.
Solution:
The solution (unlike MySQL) is to reuse already computed information about
NULL presence. Item_in_optimizer::val_int already finds out if the left IN
operand contains NULLs. The fix propagates this to the execution methods
subselect_[unique | index]subquery_engine::exec so it knows if there were
NULL values independent of the presence of keys.
In addition the patch siplifies copy_ref_key() and the logic that hanldes
the case of NULLs in the left IN operand.
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.
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.
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.
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.
- Let JTBM optimization code handle the case where the subquery is degenerate and doesn't have a
join query plan. Regular materialization would fall back to IN->EXISTS for such cases. Semi-Join
materialization does not have such option, instead we introduce and use "constant JTBM join tabs".
- Part 1 of the fix: for semi-join merged subqueries, calling child_join->optimize() until we're done with all
PS-lifetime optimizations in the parent.
Apart from the fix, the patch also adds few more unrelated test
cases for partial matching, and fixes few typos.
Analysis:
This bug uncovered that partial matching via rowid intersection
didn't handle the case when:
- the left IN argument has some NULLs,
- there are no non-null value matches, and there is no non-null
column,
- the subquery columns that are not covered with the NULLs in
the left IN argument contain at least one row, such that it
has NULL values in all columns where the left IN operand has
no NULLs.
In this case there is a partial match.
In addition the analysis of the related code uncovered incorrect
handling of few other related cases.
Solution:
The solution for the bug is to check if there exists a row with
NULLs in all columns other than the ones having NULL in the
let IN operand.
The check is implemented via checking whether the bitmaps that
store NULL information in class Ordered_key have a non-empty
intersection for the relevant columns.
The intersection itself is implemented via the function
bitmap_exists_intersection() in my_bitmap.c.
In MariaDB, when running in ONLY_FULL_GROUP_BY mode,
the server produced in incorrect error message that there
is an aggregate function without GROUP BY, for artificially
created MIN/MAX functions during subquery MIN/MAX optimization.
The fix introduces a way to distinguish between artifially
created MIN/MAX functions as a result of a rewrite, and normal
ones present in the query. The test for ONLY_FULL_GROUP_BY violation
now tests in addition if a MIN/MAX function was part of a MIN/MAX
subquery rewrite.
In order to be able to distinguish these MIN/MAX functions, the
patch introduces an additional flag in Item_in_subselect::in_strategy -
SUBS_STRATEGY_CHOSEN. This flag is set when the optimizer makes its
final choice of a subuqery strategy. In order to make the choice
consistent, access to Item_in_subselect::in_strategy is provided
via new class methods.
******
Fix MySQL BUG#12329653
In MariaDB, when running in ONLY_FULL_GROUP_BY mode,
the server produced in incorrect error message that there
is an aggregate function without GROUP BY, for artificially
created MIN/MAX functions during subquery MIN/MAX optimization.
The fix introduces a way to distinguish between artifially
created MIN/MAX functions as a result of a rewrite, and normal
ones present in the query. The test for ONLY_FULL_GROUP_BY violation
now tests in addition if a MIN/MAX function was part of a MIN/MAX
subquery rewrite.
In order to be able to distinguish these MIN/MAX functions, the
patch introduces an additional flag in Item_in_subselect::in_strategy -
SUBS_STRATEGY_CHOSEN. This flag is set when the optimizer makes its
final choice of a subuqery strategy. In order to make the choice
consistent, access to Item_in_subselect::in_strategy is provided
via new class methods.
sql/sql_insert.cc:
CREATE ... IF NOT EXISTS may do nothing, but
it is still not a failure. don't forget to my_ok it.
******
CREATE ... IF NOT EXISTS may do nothing, but
it is still not a failure. don't forget to my_ok it.
sql/sql_table.cc:
small cleanup
******
small cleanup
Problematic query:
insert ignore into `t1_federated` (`c1`) select `c1` from `t1_local` a
where not exists (select 1 from `t1_federated` b where a.c1 = b.c1);
When this query is killed in another connection it could lead to crash.
The problem is follwing:
An attempt to obtain table statistics for subselect table in killed query
fails with an error. So JOIN::optimize() for subquery is failed but
it does not prevent further subquery evaluation.
At the first subquery execution JOIN::optimize() is called
(see subselect_single_select_engine::exec()) and fails with
an error. 'executed' flag is set to TRUE and it prevents
further subquery evaluation. At the second call
JOIN::optimize() does not happen as 'JOIN::optimized' is TRUE
and in case of uncacheable subquery the 'executed' flag is set
to FALSE before subquery evaluation. So we loose 'optimize stage'
error indication (see subselect_single_select_engine::exec()).
In other words 'executed' flag is used for two purposes, for
error indication at JOIN::optimize() stage and for an
indication of subquery execution. And it seems it's wrong
as the flag could be reset.
mysql-test/r/error_simulation.result:
test case
mysql-test/t/error_simulation.test:
test case
sql/item_subselect.cc:
added new flag subselect_single_select_engine::optimize_error
which is used for error detection which could happen at optimize
stage.
sql/item_subselect.h:
added new flag subselect_single_select_engine::optimize_error
sql/sql_select.cc:
test case
- 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:
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.
The problem was that optimizer removes some outer references (it they are
constant for example) and the list of outer items built during prepare phase is
not actual during execution phase when we need it as the cache parameters.
First solution was use pointer on pointer on outer reference Item and
initialize temporary table on demand. This solved most problem except case
when optimiser also reduce Item which contains outer references ('OR' in
this bug test suite).
The solution is to build the list of outer reference items on execution
phase (after optimization) on demand (just before temporary table creation)
by walking Item tree and finding outer references among Item_ident
(Item_field/Item_ref) and Item_sum items.
Removed depends_on list (because it is not neede any mnore for the cache, in the place where it was used it replaced with upper_refs).
Added processor (collect_outer_ref_processor) and get_cache_parameters() methods to collect outer references (or other expression parameters in future).
mysql-test/r/subselect_cache.result:
A new test added.
mysql-test/r/subselect_scache.result:
Changes in creating the cache and its paremeters order or adding arguments of aggregate function (which is a parameter also, but this has no influence on the result).
mysql-test/t/subselect_cache.test:
Added a new test.
sql/item.cc:
depends_on removed.
Added processor (collect_outer_ref_processor) and get_cache_parameters() methods to collect outer references.
Item_cache_wrapper collect parameters befor initialization of its cache.
sql/item.h:
depends_on removed.
Added processor (collect_outer_ref_processor) and get_cache_parameters() methods to collect outer references.
sql/item_cmpfunc.cc:
depends_on removed.
Added processor (collect_outer_ref_processor) to collect outer references.
sql/item_cmpfunc.h:
Added processor (collect_outer_ref_processor) to collect outer references.
sql/item_subselect.cc:
depends_on removed.
Added processor get_cache_parameters() method to collect outer references.
sql/item_subselect.h:
depends_on removed.
Added processor get_cache_parameters() method to collect outer references.
sql/item_sum.cc:
Added processor (collect_outer_ref_processor) method to collect outer references.
sql/item_sum.h:
Added processor (collect_outer_ref_processor) and get_cache_parameters() methods to collect outer references.
sql/opt_range.cc:
depends_on removed.
sql/sql_base.cc:
depends_on removed.
sql/sql_class.h:
New iterator added.
sql/sql_expression_cache.cc:
Build of list of items resolved in outer query done just before creating expression cache on the first execution of the subquery which removes influence of optimizer removing items (all optimization already done).
sql/sql_expression_cache.h:
Build of list of items resolved in outer query done just before creating expression cache on the first execution of the subquery which removes influence of optimizer removing items (all optimization already done).
sql/sql_lex.cc:
depends_on removed.
sql/sql_lex.h:
depends_on removed.
sql/sql_list.h:
Added add_unique method to add only unique elements to the list.
sql/sql_select.cc:
Support of new Item list added.
sql/sql_select.h:
Support of new Item list added.
Analysis:
Both the wrong result and the valgrind warning were a result
of incomplete cleanup of the MIN/MAX subquery rewrite. At the
first execution of the query, the non-aggregate subquery is
transformed into an aggregate MIN/MAX subquery. During the
fix_fields phase of the MIN/MAX function, it sets the property
st_select_lex::with_sum_func to true.
The second execution of the query finds this flag to be ON.
When optimization reaches the same MIN/MAX subquery
transformation, it tests if the subquery is an aggregate or not.
Since select_lex->with_sum_func == true from the previous
execution, the transformation executes the second branch that
handles aggregate subqueries. This substitutes the subquery
Item into a Item_maxmin_subselect. At the same time elsewhere
it is assumed that the subquery Item is of type
Item_allany_subselect. Ultimately this results in casting the
actual object to the wrong class, and calling the wrong
any_value() method from empty_underlying_subquery().
Solution:
Cleanup the st_select_lex::with_sum_func property in the case
when the MIN/MAX transformation was performed for a non-aggregate
subquery, so that the transformation can be repeated.
Also:
1. simplified the code of the function mysql_derived_merge_for_insert.
2. moved merge of views/dt for multi-update/delete to the prepare stage.
3. the list of the references to the candidates for semi-join now is
allocated in the statement memory.
Analysis:
This is a bug in MWL#68, where it was incorrectly assumed
that if there is a match in the only non-null key, then
if there is a covering NULL row on all remaining NULL-able
columns there is a partial match. However, this is not the case,
because even if there is such a null-only sub-row, it is not
guaranteed to be part of the matched sub-row. The matched sub-row
and the NULL-only sub-row may be parts of different rows.
In fact there are two cases:
- there is a complete row with only NULL values, and
- all nullable columns contain only NULL values.
These two cases were incorrectly mixed up in the class member
subselect_partial_match_engine::covering_null_row_width.
Solution:
The solution is to:
- split covering_null_row_width into two members:
has_covering_null_row, and has_covering_null_columns, and
- take into account each state during initialization and
execution.
In addition to the bug fix explained below, the patch performs
few renames, and adds some comments to avoid similar problems.
Analysis:
The failed assert was due to a bug in MWL#68, where it was
incorrectly assumed that the size of the bitmap
subselect_rowid_merge_engine::null_only_columns should be
the same as the size of the array of Ordered_keys.
The bitmap null_only_columns contains bits to mark columns
that contain only NULLs. Therefore the indexes of the bits
to be set in null_only_columns are different from the indexes
of the Ordered_keys. If there is a NULL-only column that appears
in a table after the last partial match column with Ordered_key,
this NULL-only column would require setting a bit with index
bigger than the size of the bitmap null_only_columns.
Accessing such a bit caused the failed assert.
Solution:
Upon analysis, it turns out that null_only_columns is not needed
at all, because we are looking for partial matches, and having
such columns guarantees that there is a partial match for any
corresponding outer value.
Therefore the patch removes
subselect_rowid_merge_engine::null_only_columns.
- Added regression test with queries over the WORLD database.
- Discovered and fixed several bugs in the related cost calculation
functionality both in the semijoin and non-semijon subquery code.
- Added DBUG printing of the cost variables used to decide between
IN-EXISTS and MATERIALIZATION.
way of processing prepared statements:
- conversion subquery_predicate -> TABLE_LIST is once per-statement
- However, the code must take into account that materialized temptable
is dropped and re-created on each execution (the tricky part is that
at start of n-th EXECUTE we have TABLE_LIST object but not its TABLE object)
- IN-equality is injected into WHERE on every execution.
mysql-test/r/subselect4.result:
Moved test case for LP BUG#718593 into the correct test file subselect_mat_cost_bugs.test.
mysql-test/t/subselect4.test:
Moved test case for LP BUG#718593 into the correct test file subselect_mat_cost_bugs.test.
Resolved all conflicts, bad merges and fixed a few minor bugs in the code.
Commented out the queries from multi_update, view, subselect_sj, func_str,
derived_view, view_grant that failed either with crashes in ps-protocol or
with wrong results.
The failures are clear indications of some bugs in the code and these bugs
are to be fixed.
Analysis:
The subquery is evaluated first during ref-optimization of the outer
query because the subquery is considered constant from the perspective
of the outer query. Thus an attempt is made to evaluate the MAX subquery
and use the new constant to drive an index nested loops join.
During this evaluation the inner-most subquery replaces the JOIN_TAB
with a new one that fetches the data from a temp table.
The function select_describe crashes at the lines:
TABLE_LIST *real_table= table->pos_in_table_list;
item_list.push_back(new Item_string(real_table->alias,
strlen(real_table->alias),
cs));
because 'table' is a temp table, and it has no corresponding table
reference. This 'real_table' is NULL, and real_table->alias results
in a crash.
Solution:
In the spirit of MWL#89 prevent the evaluation of expensive predicates
during optimization. This patch prevents the evaluation of expensive
predicates during ref optimization.
sql/item_subselect.h:
Remove unused class member. Not needed for the fix, but noticed now and removed.
sql/item_subselect.cc:
Cleanup. Comments added.
sql/item_subselect.h:
Cleanup.
sql/mysql_priv.h:
Comments added.
sql/opt_subselect.cc:
The function renamed and turned to method.
Comments added.
sql/opt_subselect.h:
The function turned to method of JOIN.
sql/sql_select.cc:
Comment added. The function turned to method.
sql/sql_select.h:
The function turned to method.
mysql-test/r/explain.result:
fixed results (new item)
mysql-test/r/subselect.result:
fixed results (new item)
mysql-test/r/subselect_no_mat.result:
fixed results (new item)
mysql-test/r/subselect_no_opts.result:
fixed results (new item)
mysql-test/r/subselect_no_semijoin.result:
Fixed results (new item)
mysql-test/suite/pbxt/r/subselect.result:
Fixed results (new item)
mysql-test/t/explain.test:
Fixed results (correct behaviour)
sql/item_cmpfunc.cc:
Pass through for max/min
sql/item_subselect.cc:
moving max/min
sql/item_subselect.h:
moving max/min
sql/mysql_priv.h:
new uncacheble flags added
sql/opt_subselect.cc:
maxmin moved.
sql/opt_subselect.h:
New function for maxmin.
sql/sql_class.h:
debug code
sql/sql_lex.cc:
Fixed flags.
Limit setting fixed.
sql/sql_lex.h:
2 new flags.
sql/sql_select.cc:
Prepare divided on 2 function to be able recollect some info after transformation.
sql/sql_select.h:
Prepare divided on 2 functions.
- Fixed some issues with partitions and connection_string, which also fixed lp:716890 "Pre- and post-recovery crash in Aria"
- Fixed wrong assert in Aria
Now need to merge with latest xtradb before pushing
sql/ha_partition.cc:
Ensure that m_ordered_rec_buffer is not freed before close.
sql/mysqld.cc:
Changed to use opt_stack_trace instead of opt_pstack.
Removed references to pstack
sql/partition_element.h:
Ensure that connect_string is initialized
storage/maria/ma_key_recover.c:
Fixed wrong assert
Analysis:
The assert failed because st_select_lex::print() was called for subqueries
as follows:
Item_subselect::print() ->
subselect_single_select_engine::print() -> st_select_lex::print()
It was Item_subselect::fix_fields() that set the thd by calling set_thd(),
so when this print() was called before fix_fields(), subselect_engine::thd
was NULL.
Solution:
The patch makes all constructors of all subselect_engine classes to take
a THD parameter. The default subselect_single_select_engine engine is created
early during parse time, in the Item_subselect::init call, so we pass the
correct THD object already at this point.
--Bug#52157 various crashes and assertions with multi-table update, stored function
--Bug#54475 improper error handling causes cascading crashing failures in innodb/ndb
--Bug#57703 create view cause Assertion failed: 0, file .\item_subselect.cc, line 846
--Bug#57352 valgrind warnings when creating view
--Recently discovered problem when a nested materialized derived table is used
before being populated and it leads to incorrect result
We have several modes when we should disable subquery evaluation.
The reasons for disabling are different. It could be
uselessness of the evaluation as in case of 'CREATE VIEW'
or 'PREPARE stmt', or we should disable subquery evaluation
if tables are not locked yet as it happens in bug#54475, or
too early evaluation of subqueries can lead to wrong result
as it happened in Bug#19077.
Main problem is that if subquery items are treated as const
they are evaluated in ::fix_fields(), ::fix_length_and_dec()
of the parental items as a lot of these methods have
Item::val_...() calls inside.
We have to make subqueries non-const to prevent unnecessary
subquery evaluation. At the moment we have different methods
for this. Here is a list of these modes:
1. PREPARE stmt;
We use UNCACHEABLE_PREPARE flag.
It is set during parsing in sql_parse.cc, mysql_new_select() for
each SELECT_LEX object and cleared at the end of PREPARE in
sql_prepare.cc, init_stmt_after_parse(). If this flag is set
subquery becomes non-const and evaluation does not happen.
2. CREATE|ALTER VIEW, SHOW CREATE VIEW, I_S tables which
process FRM files
We use LEX::view_prepare_mode field. We set it before
view preparation and check this flag in
::fix_fields(), ::fix_length_and_dec().
Some bugs are fixed using this approach,
some are not(Bug#57352, Bug#57703). The problem here is
that we have a lot of ::fix_fields(), ::fix_length_and_dec()
where we use Item::val_...() calls for const items.
3. Derived tables with subquery = wrong result(Bug19077)
The reason of this bug is too early subquery evaluation.
It was fixed by adding Item::with_subselect field
The check of this field in appropriate places prevents
const item evaluation if the item have subquery.
The fix for Bug19077 fixes only the problem with
convert_constant_item() function and does not cover
other places(::fix_fields(), ::fix_length_and_dec() again)
where subqueries could be evaluated.
Example:
CREATE TABLE t1 (i INT, j BIGINT);
INSERT INTO t1 VALUES (1, 2), (2, 2), (3, 2);
SELECT * FROM (SELECT MIN(i) FROM t1
WHERE j = SUBSTRING('12', (SELECT * FROM (SELECT MIN(j) FROM t1) t2))) t3;
DROP TABLE t1;
4. Derived tables with subquery where subquery
is evaluated before table locking(Bug#54475, Bug#52157)
Suggested solution is following:
-Introduce new field LEX::context_analysis_only with the following
possible flags:
#define CONTEXT_ANALYSIS_ONLY_PREPARE 1
#define CONTEXT_ANALYSIS_ONLY_VIEW 2
#define CONTEXT_ANALYSIS_ONLY_DERIVED 4
-Set/clean these flags when we perform
context analysis operation
-Item_subselect::const_item() returns
result depending on LEX::context_analysis_only.
If context_analysis_only is set then we return
FALSE that means that subquery is non-const.
As all subquery types are wrapped by Item_subselect
it allow as to make subquery non-const when
it's necessary.
mysql-test/r/derived.result:
test case
mysql-test/r/multi_update.result:
test case
mysql-test/r/view.result:
test case
mysql-test/suite/innodb/r/innodb_multi_update.result:
test case
mysql-test/suite/innodb/t/innodb_multi_update.test:
test case
mysql-test/suite/innodb_plugin/r/innodb_multi_update.result:
test case
mysql-test/suite/innodb_plugin/t/innodb_multi_update.test:
test case
mysql-test/t/derived.test:
test case
mysql-test/t/multi_update.test:
test case
mysql-test/t/view.test:
test case
sql/item.cc:
--removed unnecessary code
sql/item_cmpfunc.cc:
--removed unnecessary checks
--THD::is_context_analysis_only() is replaced with LEX::is_ps_or_view_context_analysis()
sql/item_func.cc:
--refactored context analysis checks
sql/item_row.cc:
--removed unnecessary checks
sql/item_subselect.cc:
--removed unnecessary code
--added DBUG_ASSERT into Item_subselect::exec()
which asserts that subquery execution can not happen
if LEX::context_analysis_only is set, i.e. at context
analysis stage.
--Item_subselect::const_item()
Return FALSE if LEX::context_analysis_only is set.
It prevents subquery evaluation in ::fix_fields &
::fix_length_and_dec at context analysis stage.
sql/item_subselect.h:
--removed unnecessary code
sql/mysql_priv.h:
--Added new set of flags.
sql/sql_class.h:
--removed unnecessary code
sql/sql_derived.cc:
--added LEX::context_analysis_only analysis intialization/cleanup
sql/sql_lex.cc:
--init LEX::context_analysis_only field
sql/sql_lex.h:
--New LEX::context_analysis_only field
sql/sql_parse.cc:
--removed unnecessary code
sql/sql_prepare.cc:
--removed unnecessary code
--added LEX::context_analysis_only analysis intialization/cleanup
sql/sql_select.cc:
--refactored context analysis checks
sql/sql_show.cc:
--added LEX::context_analysis_only analysis intialization/cleanup
sql/sql_view.cc:
--added LEX::context_analysis_only analysis intialization/cleanup
Changed rows_read and rows_sent status variables to be longlong (to avoid compiler warnings)
sql/item_func.cc:
Fixed wrong usage of alias
sql/item_subselect.cc:
Changed buffer size to ulonglong to be able detect buffers bigger than size_t
sql/item_subselect.h:
Changed buffer size to ulonglong to be able detect buffers bigger than size_t
sql/multi_range_read.cc:
Fixed compiler warning by using correct type for function argument
sql/mysqld.cc:
Changed rows_read and rows_sent status variables to be longlong
sql/opt_subselect.h:
Fixed compiler warning by using correct type for function argument
sql/sql_class.cc:
Changed rows_read and rows_sent status variables to be longlong
sql/sql_class.h:
Changed rows_read and rows_sent status variables to be longlong
Changed max_nulls_in_row to uint as this is number of columns in row.
This fixed some compiler warnings.
sql/sql_select.cc:
Added casts to avoid compiler warnings
storage/heap/ha_heap.cc:
Initilize different types separate
storage/oqgraph/ha_oqgraph.cc:
Fixed argument to store(longlong) to avoid compiler warnings
Analysis:
Single-row subqueries are not considered expensive and are
evaluated both during EXPLAIN in to detect errors like
"Subquery returns more than 1 row", and during optimization to
perform constant optimization.
The cause for the failed ASSERT is in JOIN::join_free, where we set
bool full= (!select_lex->uncacheable && !thd->lex->describe);
Thus for EXPLAIN statements full == FALSE, and as a result the call to
JOIN::cleanup doesn't call JOIN_TAB::cleanup which should have
called table->disable_keyread().
Solution:
Consider all kinds of subquery predicates as expensive.
Merge 5.3-mwl89 into 5.3 main.
There is one remaining test failure in this merge:
innodb_mysql_lock2. All other tests have been checked to
deliver the same results/explains as 5.3-mwl89, including
the few remaining wrong results.
Phase 3: Implementation of re-optimization of subqueries with injected predicates
and cost comparison between Materialization and IN->EXISTS strategies.
The commit contains the following known problems:
- The implementation of EXPLAIN has not been re-engineered to reflect the
changes in subquery optimization. EXPLAIN for subqueries is called during
the execute phase, which results in different code paths during JOIN::optimize
and thus in differing EXPLAIN messages for constant/system tables.
- There are some valgrind warnings that need investigation
- Several EXPLAINs with minor differences need to be reconsidered after fixing
the EXPLAIN problem above.
This patch also adds one extra optimizer_switch: 'in_to_exists' for complete
manual control of the subquery execution strategies.
Fix some bugs where we stored values other than 0 or 1 in my_bool
Fixed some compiler warnings
client/mysql.cc:
Changed interrupted_query from my_bool to int, as we stored 2 in it.
client/mysqladmin.cc:
Changed return variable type to same type as function value type
client/mysqltest.cc:
Changed 'found' to int as we store other values than 0 or 1 into it
Changed type for parameter of set_reconnect() to match usage.
extra/libevent/evbuffer.c:
Added __attribute__((unused))
extra/libevent/event.c:
Added __attribute__((unused))
extra/libevent/signal.c:
Added __attribute__((unused))
sql/event_data_objects.h:
my_bool -> bool
sql/event_db_repository.cc:
my_bool -> bool
sql/event_db_repository.h:
my_bool -> bool
sql/event_parse_data.h:
my_bool -> bool
sql/events.cc:
my_bool -> bool
sql/events.h:
my_bool -> bool
sql/field.cc:
my_bool -> bool
sql/field.h:
my_bool -> bool
sql/hash_filo.h:
my_bool -> bool
sql/item.cc:
my_bool -> bool
sql/item.h:
my_bool -> bool
sql/item_cmpfunc.h:
my_bool -> bool
Changed result_for_null_param from my_bool to int as we stored -1 in it.
sql/item_func.cc:
my_bool -> bool
Modified udf wrapper functions so that the UDF functions would continue to use my_bool. (To keep compatibility with UDF:s)
sql/item_func.h:
my_bool -> bool
sql/item_subselect.h:
my_bool -> bool
sql/item_sum.cc:
Modified udf wrapper functions so that the UDF functions would continue to use my_bool. (To keep compatibility with UDF:s)
sql/parse_file.h:
my_bool -> bool
sql/rpl_mi.h:
my_bool -> bool
sql/sp_rcontext.h:
my_bool -> bool
sql/sql_analyse.h:
my_bool -> bool
sql/sql_base.cc:
Change some assignments so that we don't initialize bool variables with int's.
sql/sql_bitmap.h:
my_bool -> bool
sql/sql_cache.cc:
my_bool -> bool
sql/sql_cache.h:
my_bool -> bool
sql/sql_class.h:
my_bool -> bool
sql/sql_insert.cc:
Change some assignments so that we don't initialize bool variables with int's.
sql/sql_prepare.cc:
my_bool -> bool
sql/table.h:
my_bool -> bool
storage/maria/ma_check.c:
Removed duplicate assignment
strings/decimal.c:
Fixed wrong variable usage.
Don't do complex arithmetic on bool when simple works.
Step2 in the separation of the creation of IN->EXISTS equi-join conditions from
their injection. The goal of this separation is to make it possible that the
IN->EXISTS conditions can be used for cost estimation without actually modifying
the subquery.
This patch separates row_value_in_to_exists_transformer() into two methods:
- create_row_value_in_to_exists_cond(), and
- inject_row_value_in_to_exists_cond()
The patch performs minimal refactoring of the code so that it is easier to solve
problems resulting from the separation. There is a lot to be simplified in this
code, but this will be done separately.
Step1 in the separation of the creation of IN->EXISTS equi-join conditions from
their injection. The goal of this separation is to make it possible that the
IN->EXISTS conditions can be used for cost estimation without actually modifying
the subquery.
This patch separates single_value_in_to_exists_transformer() into two methods:
- create_single_value_in_to_exists_cond(), and
- inject_single_value_in_to_exists_cond()
The patch performs minimal refactoring of the code so that it is easier to solve
problems resulting from the separation. There is a lot to be simplified in this
code, but this will be done separately.
1. Changed the lazy optimization for subqueries that can be
materialized into bottom-up optimization during the optimization of
the main query.
The main change is implemented by the method
Item_in_subselect::setup_engine.
All other changes were required to correct problems resulting from
changing the order of optimization. Most of these problems followed
the same pattern - there are some shared structures between a
subquery and its parent query. Depending on which one is optimized
first (parent or child query), these shared strucutres may get
different values, thus resulting in an inconsistent query plan.
2. Changed the code-generation for subquery materialization to be
performed in runtime memory for each (re)execution, instead of in
statement memory (once per prepared statement).
- Item_in_subselect::setup_engine() no longer creates materialization
related objects in statement memory.
- Merged subselect_hash_sj_engine::init_permanent and
subselect_hash_sj_engine::init_runtime into
subselect_hash_sj_engine::init, which is called for each
(re)execution.
- Fixed deletion of the temp table accordingly.
mysql-test/r/subselect_mat.result:
Adjusted changed EXPLAIN because of earlier optimization of subqueries.
libmysqld/Makefile.am:
The new file added.
mysql-test/r/index_merge_myisam.result:
subquery_cache optimization option added.
mysql-test/r/myisam_mrr.result:
subquery_cache optimization option added.
mysql-test/r/subquery_cache.result:
The subquery cache tests added.
mysql-test/r/subselect3.result:
Subquery cache switched off to avoid changing read statistics.
mysql-test/r/subselect3_jcl6.result:
Subquery cache switched off to avoid changing read statistics.
mysql-test/r/subselect_no_mat.result:
subquery_cache optimization option added.
mysql-test/r/subselect_no_opts.result:
subquery_cache optimization option added.
mysql-test/r/subselect_no_semijoin.result:
subquery_cache optimization option added.
mysql-test/r/subselect_sj.result:
subquery_cache optimization option added.
mysql-test/r/subselect_sj_jcl6.result:
subquery_cache optimization option added.
mysql-test/t/subquery_cache.test:
The subquery cache tests added.
mysql-test/t/subselect3.test:
Subquery cache switched off to avoid changing read statistics.
sql/CMakeLists.txt:
The new file added.
sql/Makefile.am:
The new files added.
sql/item.cc:
Expression cache item (Item_cache_wrapper) added.
Item_ref and Item_field fixed for correct usage of result field and fast resolwing in SP.
sql/item.h:
Expression cache item (Item_cache_wrapper) added.
Item_ref and Item_field fixed for correct usage of result field and fast resolwing in SP.
sql/item_cmpfunc.cc:
Subquery cache added.
sql/item_cmpfunc.h:
Subquery cache added.
sql/item_subselect.cc:
Subquery cache added.
sql/item_subselect.h:
Subquery cache added.
sql/item_sum.cc:
Registration of subquery parameters added.
sql/mysql_priv.h:
subquery_cache optimization option added.
sql/mysqld.cc:
subquery_cache optimization option added.
sql/opt_range.cc:
Fix due to subquery cache.
sql/opt_subselect.cc:
Parameters of the function cahnged.
sql/procedure.h:
.h file guard added.
sql/sql_base.cc:
Registration of subquery parameters added.
sql/sql_class.cc:
Option to allow add indeces to temporary table.
sql/sql_class.h:
Item iterators added.
Option to allow add indeces to temporary table.
sql/sql_expression_cache.cc:
Expression cache for caching subqueries added.
sql/sql_expression_cache.h:
Expression cache for caching subqueries added.
sql/sql_lex.cc:
Registration of subquery parameters added.
sql/sql_lex.h:
Registration of subqueries and subquery parameters added.
sql/sql_select.cc:
Subquery cache added.
sql/sql_select.h:
Subquery cache added.
sql/sql_union.cc:
A new parameter to the function added.
sql/sql_update.cc:
A new parameter to the function added.
sql/table.cc:
Procedures to manage temporarty tables index added.
sql/table.h:
Procedures to manage temporarty tables index added.
storage/maria/ha_maria.cc:
Fix of handler to allow destoy a table in case of error during the table creation.
storage/maria/ha_maria.h:
.h file guard added.
storage/myisam/ha_myisam.cc:
Fix of handler to allow destoy a table in case of error during the table creation.
