MDEV-27277 added warnings on truncation during sorting for SELECTs
but did not for DML operations. However, UPDATEs and DELETEs may also
perform sorting and thus produce warnings. This commit fixes that
Single-table UPDATE/DELETE didn't provide outer_lookup_keys value for
subqueries. This didn't allow to make a meaningful choice between
IN->EXISTS and Materialization strategies for subqueries.
Fix this:
* Make UPDATE/DELETE save Sql_cmd_dml::scanned_rows,
* Then, subquery's JOIN::choose_subquery_plan() can fetch it from
there for outer_lookup_keys
Details:
UPDATE/DELETE now calls select_lex->optimize_unflattened_subqueries()
twice, like SELECT does (first call optimize_constant_subquries() in
JOIN::optimize_inner(), then call optimize_unflattened_subqueries() in
JOIN::optimize_stage2()):
1. Call with const_only=true before any optimizations. This allows
range optimizer and others to use the values of cheap const
subqueries.
2. Call it with const_only=false after range optimizer, partition
pruning, etc. outer_lookup_keys value is provided, so it's possible to
pick a good subquery strategy.
Note: PROTECT_STATEMENT_MEMROOT requires that first SP execution
performs subquery optimization for all subqueries, even for degenerate
query plans like "Impossible WHERE". Due to that, we ensure that the
call to optimize_unflattened_subqueries (with const_only=false) even
for degenerate query plans still happens, as was the case before this
change.
During a query execution some sorting and grouping operations
on strings may be involved. System variable max_sort_length defines
the maximum number of bytes to use when comparing strings during
sorting/grouping. Thus, the comparable parts of strings may be less
than their actual size, so the results of the query may be not
sorted/grouped properly.
To indicate that some comparisons were done on a truncated lengths,
a new warning has been introduced with this commit.
Adding support for the ROW data type in the stored function RETURNS clause:
- explicit ROW(..members...) for both sql_mode=DEFAULT and sql_mode=ORACLE
CREATE FUNCTION f1() RETURNS ROW(a INT, b VARCHAR(32)) ...
- anchored "ROW TYPE OF [db1.]table1" declarations for sql_mode=DEFAULT
CREATE FUNCTION f1() RETURNS ROW TYPE OF test.t1 ...
- anchored "[db1.]table1%ROWTYPE" declarations for sql_mode=ORACLE
CREATE FUNCTION f1() RETURN test.t1%ROWTYPE ...
Adding support for anchored scalar data types in RETURNS clause:
- "TYPE OF [db1.]table1.column1" for sql_mode=DEFAULT
CREATE FUNCTION f1() RETURNS TYPE OF test.t1.column1;
- "[db1.]table1.column1" for sql_mode=ORACLE
CREATE FUNCTION f1() RETURN test.t1.column1%TYPE;
Details:
- Adding a new sql_mode_t parameter to
sp_head::create()
sp_head::sp_head()
sp_package::create()
sp_package::sp_package()
to guarantee early initialization of sp_head::m_sql_mode.
Before this change, this member was not initialized at all during
CREATE FUNCTION/PROCEDURE/PACKAGE statements, and was not used.
Now it needs to be initialized to write properly the
mysql.proc.returns column, according to the create time sql_mode.
- Code refactoring to make the things simpler and functions smaller:
* Adding a new method
Field_row::row_create_fields(THD *thd, List<Spvar_definition> *list)
to make a Virtual_tmp_table with Fields for ROW members
from an explicit definition.
* Adding a new method
Field_row::row_create_fields(THD *thd, const Spvar_definition &def)
to make a Virtual_tmp_table with Fields for ROW members
from an explicit or a table anchored definition.
* Adding a new method
Item_args::add_array_of_item_field(THD *thd, const Virtual_tmp_table &vtable)
to create and array of Item_field corresponding to all Field instances
in a Virtual_tmp_table
* Removing Item_field_row::row_create_items(). It was decomposed
into the new methods described above.
* Moving the code from the loop body in sp_rcontext::init_var_items()
into a separate method Spvar_definition::make_item_field_row(),
to make the code clearer (smaller functions).
make_item_field_row() itself uses the new methods described above.
- Changing the data type of sp_head::m_return_field_def
from Column_definition to Spvar_definition.
So now it supports not only SQL column field types,
but also explicit ROW and anchored ROW data types,
as well as anchored column types.
- Adding a new Column_definition parameter to sp_head::create_result_field().
Before this patch, create_result_field() took the definition only
from m_return_field_def. Now it's also called with a local Column_definition
variable which contains the explicit definition resolved from an
anchored defition.
- Modifying sql_yacc.yy to support the new grammar.
Adding new helper methods:
* sf_return_fill_definition_row()
* sf_return_fill_definition_rowtype_of()
* sf_return_fill_definition_type_of()
- Fixing tests in:
* Virtual_tmp_table::setup_field_pointers() in sql_select.cc
* Send_field::normalize() in field.h
* store_column_type()
to prevent calling Type_handler_row::field_type(),
which is implemented a DBUG_ASSERT(0).
Before this patch the affected methods and functions were called only
for scalar data types. Now ROW is also possible.
- Adding a new virtual method Field::cols()
- Overriding methods:
Item_func_sp::cols()
Item_func_sp::element_index()
Item_func_sp::check_cols()
Item_func_sp::bring_value()
to support the ROW data type.
- Extending the rule sp_return_type to support
* explicit ROW and anchored ROW data types
* anchored scalar data types
- Overriding Field_row::sql_type() to print
the data type of an explicit ROW.
Extend derived table syntax to support column name assignment.
(subquery expression) [as|=] ident [comma separated column name list].
Prior to this patch, the optional comma separated column name list is
not supported.
Processing within the unit of the subquery expression will use
original column names, outside the unit will use the new names.
For example, in the query
select a1, a2 from
(select c1, c2, c3 from t1 where c2 > 0) as dt (a1, a2, a3)
where a2 > 10;
we see the second column of the derived table dt being used both within,
(where c2 > 0), and outside, (where a2 > 10), the specification.
Both conditions apply to t1.c2.
When multiple unit preparations are required, such as when being used within
a prepared statement or procedure, original column names are needed for
correct resolution. Original names are reset within mysql_derived_reinit().
Item_holder items, used for result tables in both TVC and union preparations
are renamed before use within st_select_lex_unit::prepare().
During wildcard expansion, if column names are present, items names are
set directly after creation.
Reviewed by Igor Babaev (igor@mariadb.com)
A call to
dbug_print_join_prefix(join_positions, idx, s)
returns a const char* ponter to string with current join prefix,
including the table being added to it.
(Variant 4, with @@optimizer_adjust_secondary_key_costs, reuse in two
places, and conditions are replaced with equivalent simpler forms in two more)
In best_access_path(), ReuseRangeEstimateForRef-3, the check
for whether
"all used key_part_i used key_part_i=const"
was incorrect: it may produced a "NO" answer for cases when we
had:
key_part1= const // some key parts are usable
key_part2= value_not_in_join_prefix //present but unusable
key_part3= non_const_value // unusable due to gap in key parts.
This caused the optimizer to fail to apply ReuseRangeEstimateForRef
heuristics. The consequence is poor query plan choice when the index
in question has very skewed data distribution.
The fix is enabled if its @@optimizer_adjust_secondary_key_costs flag
is set.
The memory leak happened on second execution of a prepared statement
that runs UPDATE statement with correlated subquery in right hand side of
the SET clause. In this case, invocation of the method
table->stat_records()
could return the zero value that results in going into the 'if' branch
that handles impossible where condition. The issue is that this condition
branch missed saving of leaf tables that has to be performed as first
condition optimization activity. Later the PS statement memory root
is marked as read only on finishing first time execution of the prepared
statement. Next time the same statement is executed it hits the assertion
on attempt to allocate a memory on the PS memory root marked as read only.
This memory allocation takes place by the sequence of the following
invocations:
Prepared_statement::execute
mysql_execute_command
Sql_cmd_dml::execute
Sql_cmd_update::execute_inner
Sql_cmd_update::update_single_table
st_select_lex::save_leaf_tables
List<TABLE_LIST>::push_back
To fix the issue, add the flag SELECT_LEX::leaf_tables_saved to control
whether the method SELECT_LEX::save_leaf_tables() has to be called or
it has been already invoked and no more invocation required.
Similar issue could take place on running the DELETE statement with
the LIMIT clause in PS/SP mode. The reason of memory leak is the same as for
UPDATE case and be fixed in the same way.
(Variant 2b: call greedy_search() twice, correct handling for limited
search_depth)
Modify the join optimizer to specifically try to produce join orders that
can short-cut their execution for ORDER BY..LIMIT clause.
The optimization is controlled by @@optimizer_join_limit_pref_ratio.
Default value 0 means don't construct short-cutting join orders.
Other value means construct short-cutting join order, and prefer it only
if it promises speedup of more than #value times.
In Optimizer Trace, look for these names:
* join_limit_shortcut_is_applicable
* join_limit_shortcut_plan_search
* join_limit_shortcut_choice
Discovered this while working on MDEV-34720: test_if_cheaper_ordering()
uses rec_per_key, while the original estimate for the access method
is produced in best_access_path() by using actual_rec_per_key().
Make test_if_cheaper_ordering() also use actual_rec_per_key().
Also make several getter function "const" to make this compile.
Also adjusted the testcase to handle this (the change backported from
11.0)
Before this patch the crash occured when a single row dataset is used and
Item::remove_eq_conds() is called for HAVING. This function is not supposed
to be called after the elimination of multiple equalities.
To fix this problem instead of Item::remove_eq_conds() Item::val_int() is
used. In this case the optimizer tries to evaluate the condition for the
single row dataset and discovers impossible HAVING immediately. So, the
execution phase is skipped.
Approved by Igor Babaev <igor@maridb.com>
New runtime diagnostic introduced with MDEV-34490 has detected
that `Item_int_with_ref` incorrectly returns an instance of its ancestor
class `Item_int`. This commit fixes that.
In addition, this commit reverts a part of the diagnostic related
to `clone_item()` checks. As it turned out, `clone_item()` is not required
to return an object of the same class as the cloned one. For example,
look at `Item_param::clone_item()`: it can return objects of `Item_null`,
`Item_int`, `Item_string`, etc, depending on the object state.
So the runtime type diagnostic is not applicable to `clone_item()` and
is disabled with this commit.
As the similar diagnostic failures are expected to appear again
in the future, this commit introduces a new test file in the main suite:
item_types.test, and new test cases may be added to this file
Reviewer: Oleksandr Byelkin <sanja@mariadb.com>
The `Item` class methods `get_copy()`, `build_clone()`, and `clone_item()`
face an issue where they may be defined in a descendant class
(e.g., `Item_func`) but not in a further descendant (e.g., `Item_func_child`).
This can lead to scenarios where `build_clone()`, when operating on an
instance of `Item_func_child` with a pointer to the base class (`Item`),
returns an instance of `Item_func` instead of `Item_func_child`.
Since this limitation cannot be resolved at compile time, this commit
introduces runtime type checks for the copy/clone operations.
A debug assertion will now trigger in case of a type mismatch.
`get_copy()`, `build_clone()`, and `clone_item()` are no more virtual,
but virtual `do_get_copy()`, `do_build_clone()`, and `do_clone_item()`
are added to the protected section of the class `Item`.
Additionally, const qualifiers have been added to certain methods
to enhance code reliability.
Reviewer: Oleksandr Byelkin <sanja@mariadb.com>
