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
The code in best_access_path() uses PREV_BITS(uint, N) to
compute a bitmap of all keyparts: {keypart0, ... keypart{N-1}).
The problem is that PREV_BITS($type, N) macro code can't handle the case
when N=<number of bits in $type).
Also, why use PREV_BITS(uint, ...) for key part map computations when
we could have used PREV_BITS(key_part_map) ?
Fixed both:
- Change PREV_BITS(type, N) to handle any N in [0; n_bits(type)].
- Change PREV_BITS() to use key_part_map when computing key_part_map bitmaps.
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.
When a derived table which has distinct values and BLOB fields is
materialized, an index is created over all columns to ensure only
unique values are placed to the result.
This index is created in a special mode HA_UNIQUE_HASH to support BLOBs.
Later the optimizer may incorrectly choose this index to retrieve values
from the derived table, although such type of index cannot be used
for data retrieval.
This commit excludes HA_UNIQUE_HASH indexes from adding to
`JOIN::keyuse` array thus preventing their subsequent usage for
data retrieval
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.
Assertion failure has happened due to this scenario:
A query was ran with optimizer_join_limit_pref_ratio=1.
The query had "ORDER BY t1.col LIMIT N".
The optimizer set join->limit_shortcut_applicable=1.
Then, table t1 was marked as constant.
The code in choose_query_plan() still set join->limit_optimization_mode=1
which caused the optimizer to only consider t1 as the first non-const table.
But t1 was already put into the join prefix as the constant table.
The optimizer couldn't produce any join order at all and crashed.
Fixed by not searching for shortcut plan if ORDER BY table is a constant.
We will not try to do sorting anyway in this case (and LIMIT short-cutting
will be done for any join order).
(Variant 2: only allow rewrite for ref(const))
make_join_select() has a "ref_to_range" rewrite: it would rewrite
any ref access to a range access on the same index if the latter uses
more keyparts.
It seems, he initial intent of this was to fix poor query plan choice
in cases like
t.keypart1=const AND t.keypart2 < 'foo'
Due to deficiency in cost model, ref access could be picked while range
would enumerate fewer rows and be cheaper.
However, the condition also forces a rewrite in cases like:
t.keypart1=prev_table.col AND t.keypart1<='foo' AND t.keypart2<'bar'
Here, it can be that
* keypart1=prev_table.col is highly selective
* (keypart1, keypart2) <= ('foo', 'bar') is not at all selective.
Still, the rewrite would be made and poor query plan chosen.
Fixed this by only doing the rewrite if ref access was ref(const)
so we can be certain that quick select also used these restrictions
and will scan a subset of rows that ref access would scan.
Pre-11.0 variant:
1. In recompute_join_cost_with_limit(), add an assertion that that
partial_join_cost >= 0.0.
2. best_extension_by_limited_search() subtracts COST_EPS from
join->best_read. But it is not subtracted from
join->positions[0].read_time, add it back.
2. We could get very small negative partial_join_cost due to rounding
errors. For fraction=1.0, we were computing essentially this (denote
as EXPR-1):
$row_read_cost + $where_cost - ($row_read_cost + $where_cost)
which should compute to 0.
But the computation was done in the following order (left-to-right):
EXPR-2:
($row_read_cost + $where_cost) - $row_read_cost - $where_cost
this produced a value of -1.1102230246251565e-16 due to a rounding
error. Change the computation use EXPR-1 instead of EXPR-2.
optimize_straight_join and best_extension_by_limited_search()
use 0.001 to make choice between plans with identical cost deterministic.
Use COST_EPS instead of 0.001, like it's done in newer versions.
Variant for 11.2+:
In recompute_join_cost_with_limit(), do not subtract the cost of checking
the WHERE:
pos->records_read* WHERE_COST_THD(join->thd)
It is already included in pos->read_time.
Also added comments about difference between this fix and the pre-11.2
variant.
Stop skipping const items when selecting but skip them when storing
their results to spider row to avoid storing in mismatching temporary
table fields.
Skip auxiliary fields in SELECTing, and do not store
the (non-existing) results to the corresponding temporary table
accordingly.
When there are BOTH auxiliary fields AND const items in the auxiliary
field items, do not use the spider GBH. This is a rare occasion if it
happens at all and not worth the added complexity to cover it.
Use the original item (item_ptr) in constructing GROUP BY and ORDER
BY, which also means using item->name instead of field->field_name as
aliases in constructing SELECT items. This fixes spurious regressions
caused by the above changes in some tests using ORDER BY, such as
mdev_24517.test. As a by-product, this also fixes MDEV-29546.
Therefore we update mdev_29008.test to include the MDEV-29546 case.
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)
Field_blob::store() has special code for GROUP_CONCAT temporary table
(to store blob values in Blob_mem_storage - this prevents them
from being freed/overwritten when a next row is read).
Field_geom and Field_blob_compressed inherit from Field_blob but they
have their own ::store() method without this special Blob_mem_storage
support.
Considering that non-grouping CONCAT() of such fields converts
them to plain BLOB, let's do the same for GROUP_CONCAT. To do it,
Item_func_group_concat::setup will signal that it's creating
a temporary table for GROUP_CONCAT, and Field_blog::make_new_field()
override will create base Field_blob when under group concat.
Search conditions were evaluated using val_int(), which was wrong.
Fixing the code to use val_bool() instead.
Details:
- Adding a new item_base_t::IS_COND flag which marks Items used
as <search condition> in WHERE, HAVING, JOIN ON, CASE WHEN clauses.
The flag is at the parse time.
These expressions must be evaluated using val_bool() rather than val_int().
Note, the optimizer creates more Items which are used as search conditions.
Most of these items are not marked with IS_COND yet. This is OK for now,
but eventually these Items can also be fixed to have the flag.
- Adding a method Item::is_cond() which tests if the Item has the IS_COND flag.
- Implementing Item_cache_bool. It evaluates the cached expression using
val_bool() rather than val_int().
Overriding Type_handler_bool::Item_get_cache() to create Item_cache_bool.
- Implementing Item::save_bool_in_field(). It uses val_bool() rather than
val_int() to evaluate the expression.
- Implementing Type_handler_bool::Item_save_in_field()
using Item::save_bool_in_field().
- Fixing all Item_bool_func descendants to implement a virtual val_bool()
rather than a virtual val_int().
- To find places where val_int() should be fixed to val_bool(), a few
DBUG_ASSERT(!is_cond()) where added into val_int() implementations
of selected (most frequent) classes:
Item_field
Item_str_func
Item_datefunc
Item_timefunc
Item_datetimefunc
Item_cache_bool
Item_bool_func
Item_func_hybrid_field_type
Item_basic_constant descendants
- Fixing all places where DBUG_ASSERT() happened during an "mtr" run
to use val_bool() instead of val_int().
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)
