MySQL 8.0.29
Source Code Documentation
sql_optimizer.h
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1#ifndef SQL_OPTIMIZER_INCLUDED
2#define SQL_OPTIMIZER_INCLUDED
3
4/* Copyright (c) 2000, 2022, Oracle and/or its affiliates.
5
6 This program is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License, version 2.0,
8 as published by the Free Software Foundation.
9
10 This program is also distributed with certain software (including
11 but not limited to OpenSSL) that is licensed under separate terms,
12 as designated in a particular file or component or in included license
13 documentation. The authors of MySQL hereby grant you an additional
14 permission to link the program and your derivative works with the
15 separately licensed software that they have included with MySQL.
16
17 This program is distributed in the hope that it will be useful,
18 but WITHOUT ANY WARRANTY; without even the implied warranty of
19 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
20 GNU General Public License, version 2.0, for more details.
21
22 You should have received a copy of the GNU General Public License
23 along with this program; if not, write to the Free Software
24 Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA */
25
26/**
27 @file sql/sql_optimizer.h
28 Classes used for query optimizations.
29*/
30
31#include <sys/types.h>
32
33#include <cstring>
34#include <memory>
35#include <utility>
36
37#include "field_types.h"
38#include "my_alloc.h"
39#include "my_base.h"
40#include "my_dbug.h"
41#include "my_table_map.h"
42#include "sql/field.h"
43#include "sql/item.h"
45#include "sql/mem_root_array.h"
46#include "sql/opt_explain_format.h" // Explain_sort_clause
47#include "sql/sql_executor.h"
48#include "sql/sql_lex.h"
49#include "sql/sql_list.h"
51#include "sql/sql_select.h" // Key_use
52#include "sql/table.h"
54
55enum class Subquery_strategy : int;
56class COND_EQUAL;
57class Item_subselect;
58class Item_sum;
60class THD;
61class Window;
62struct AccessPath;
63struct MYSQL_LOCK;
64
65class Item_equal;
66template <class T>
67class mem_root_deque;
68
69// Key_use has a trivial destructor, no need to run it from Mem_root_array.
71
73
74/*
75 This structure is used to collect info on potentially sargable
76 predicates in order to check whether they become sargable after
77 reading const tables.
78 We form a bitmap of indexes that can be used for sargable predicates.
79 Only such indexes are involved in range analysis.
80*/
81
83 Field *field; /* field against which to check sargability */
84 Item **arg_value; /* values of potential keys for lookups */
85 uint num_values; /* number of values in the above array */
86};
87
88/**
89 Wrapper for ORDER* pointer to trace origins of ORDER list
90
91 As far as ORDER is just a head object of ORDER expression
92 chain, we need some wrapper object to associate flags with
93 the whole ORDER list.
94*/
96 public:
97 ORDER *order; ///< ORDER expression that we are wrapping with this class
98 Explain_sort_clause src; ///< origin of order list
99
100 private:
101 int flags; ///< bitmap of Explain_sort_property
102
103 public:
105
107 : order(order_arg),
108 src(src_arg),
109 flags(order_arg ? ESP_EXISTS : ESP_none) {}
110
111 bool empty() const { return order == nullptr; }
112
113 void clean() {
114 order = nullptr;
115 src = ESC_none;
116 flags = ESP_none;
117 }
118
119 int get_flags() const {
120 assert(order);
121 return flags;
122 }
123};
124
125class JOIN {
126 public:
127 JOIN(THD *thd_arg, Query_block *select);
128 JOIN(const JOIN &rhs) = delete;
129 JOIN &operator=(const JOIN &rhs) = delete;
130
131 /// Query expression referring this query block
134 }
135
136 /// Query block that is optimized and executed using this JOIN
138 /// Thread handler
139 THD *const thd;
140
141 /**
142 Optimal query execution plan. Initialized with a tentative plan in
143 JOIN::make_join_plan() and later replaced with the optimal plan in
144 get_best_combination().
145 */
147 /// Array of QEP_TABs
148 QEP_TAB *qep_tab{nullptr};
149
150 /**
151 Array of plan operators representing the current (partial) best
152 plan. The array is allocated in JOIN::make_join_plan() and is valid only
153 inside this function. Initially (*best_ref[i]) == join_tab[i].
154 The optimizer reorders best_ref.
155 */
156 JOIN_TAB **best_ref{nullptr};
157 /// mapping between table indexes and JOIN_TABs
158 JOIN_TAB **map2table{nullptr};
159 /*
160 The table which has an index that allows to produce the requried ordering.
161 A special value of 0x1 means that the ordering will be produced by
162 passing 1st non-const table to filesort(). NULL means no such table exists.
163 */
165
166 // Temporary tables that need to be cleaned up after the query.
167 // Only used for the hypergraph optimizer; the non-hypergraph optimizer
168 // uses QEP_TABs to hold the list of tables (including temporary tables).
171
172 // Allocated on the MEM_ROOT, but can hold some objects
173 // that allocate on the heap and thus need destruction.
175 };
178
179 // Similarly, filesorts that need to be cleaned up after the query.
180 // Only used for the hypergraph optimizer, for the same reason as above.
182
183 /**
184 Before plan has been created, "tables" denote number of input tables in the
185 query block and "primary_tables" is equal to "tables".
186 After plan has been created (after JOIN::get_best_combination()),
187 the JOIN_TAB objects are enumerated as follows:
188 - "tables" gives the total number of allocated JOIN_TAB objects
189 - "primary_tables" gives the number of input tables, including
190 materialized temporary tables from semi-join operation.
191 - "const_tables" are those tables among primary_tables that are detected
192 to be constant.
193 - "tmp_tables" is 0, 1 or 2 (more if windows) and counts the maximum
194 possible number of intermediate tables in post-processing (ie sorting and
195 duplicate removal).
196 Later, tmp_tables will be adjusted to the correct number of
197 intermediate tables, @see JOIN::make_tmp_tables_info.
198 - The remaining tables (ie. tables - primary_tables - tmp_tables) are
199 input tables to materialized semi-join operations.
200 The tables are ordered as follows in the join_tab array:
201 1. const primary table
202 2. non-const primary tables
203 3. intermediate sort/group tables
204 4. possible holes in array
205 5. semi-joined tables used with materialization strategy
206 */
207 uint tables{0}; ///< Total number of tables in query block
208 uint primary_tables{0}; ///< Number of primary input tables in query block
209 uint const_tables{0}; ///< Number of primary tables deemed constant
210 uint tmp_tables{0}; ///< Number of temporary tables used by query
212 /**
213 Indicates that the data will be aggregated (typically GROUP BY),
214 _and_ that it is already processed in an order that is compatible with
215 the grouping in use (e.g. because we are scanning along an index,
216 or because an earlier step sorted the data in a group-compatible order).
217
218 Note that this flag changes value at multiple points during optimization;
219 if it's set when a temporary table is created, this means we aggregate
220 into said temporary table (end_write_group is chosen instead of end_write),
221 but if it's set later, it means that we can aggregate as we go,
222 just before sending the data to the client (end_send_group is chosen
223 instead of end_send).
224
225 @see make_group_fields, alloc_group_fields, JOIN::exec
226 */
228 /// If query contains GROUP BY clause
230 /// If true, send produced rows using query_result
231 bool do_send_rows{true};
232 /// Set of tables contained in query
234 table_map const_table_map; ///< Set of tables found to be const
235 /**
236 Const tables which are either:
237 - not empty
238 - empty but inner to a LEFT JOIN, thus "considered" not empty for the
239 rest of execution (a NULL-complemented row will be used).
240 */
242 /**
243 This is the bitmap of all tables which are dependencies of
244 lateral derived tables which are not (yet) part of the partial
245 plan. (The value is a logical 'or' of zero or more
246 TABLE_LIST.map() values.)
247
248 When we are building the join order, there is a partial plan (an
249 ordered sequence of JOIN_TABs), and an unordered set of JOIN_TABs
250 not yet added to the plan. Due to backtracking, the partial plan
251 may both grow and shrink. When we add a new table to the plan, we
252 may wish to set up join buffering, so that rows from the preceding
253 table are buffered. If any of the remaining tables are derived
254 tables that depends on any of the predecessors of the table we
255 are adding (i.e. a lateral dependency), join buffering would be
256 inefficient. (@see setup_join_buffering() for a detailed
257 explanation of why this is so.)
258
259 For this reason we need to maintain this table_map of lateral
260 dependencies of tables not yet in the plan. Whenever we add a new
261 table to the plan, we update the map by calling
262 Optimize_table_order::recalculate_lateral_deps_incrementally().
263 And when we remove a table, we restore the previous map value
264 using a Tabel_map_restorer object.
265
266 As an example, assume that we join four tables, t1, t2, t3 and
267 d1, where d1 is a derived table that depends on t1:
268
269 SELECT * FROM t1 JOIN t2 ON t1.a=t2.b JOIN t3 ON t2.c=t3.d
270 JOIN LATERAL (SELECT DISTINCT e AS x FROM t4 WHERE t4.f=t1.c)
271 AS d1 ON t3.e=d1.x;
272
273 Now, if our partial plan is t1->t2, the map (of lateral
274 dependencies of the remaining tables) will contain t1.
275 This tells us that we should not use join buffering when joining t1
276 with t2. But if the partial plan is t1->d2->t2, the map will be
277 empty. We may thus use join buffering when joining d2 with t2.
278 */
280
281 /* Number of records produced after join + group operation */
286 // m_select_limit is used to decide if we are likely to scan the whole table.
288 /**
289 Used to fetch no more than given amount of rows per one
290 fetch operation of server side cursor.
291 The value is checked in end_send and end_send_group in fashion, similar
292 to offset_limit_cnt:
293 - fetch_limit= HA_POS_ERROR if there is no cursor.
294 - when we open a cursor, we set fetch_limit to 0,
295 - on each fetch iteration we add num_rows to fetch to fetch_limit
296 */
298
299 /**
300 This is the result of join optimization.
301
302 @note This is a scratch array, not used after get_best_combination().
303 */
305
306 /******* Join optimization state members start *******/
307
308 /* Current join optimization state */
310
311 /* We also maintain a stack of join optimization states in * join->positions[]
312 */
313 /******* Join optimization state members end *******/
314
315 /// A hook that secondary storage engines can use to override the executor
316 /// completely.
319
320 /**
321 The cost of best complete join plan found so far during optimization,
322 after optimization phase - cost of picked join order (not taking into
323 account the changes made by test_if_skip_sort_order()).
324 */
325 double best_read{0.0};
326 /**
327 The estimated row count of the plan with best read time (see above).
328 */
330 /// Expected cost of filesort.
331 double sort_cost{0.0};
332 /// Expected cost of windowing;
333 double windowing_cost{0.0};
337
338 // For destroying fields otherwise owned by RemoveDuplicatesIterator.
340
341 Item_sum **sum_funcs{nullptr};
342 /**
343 Describes a temporary table.
344 Each tmp table has its own tmp_table_param.
345 The one here is transiently used as a model by create_intermediate_table(),
346 to build the tmp table's own tmp_table_param.
347 */
350
351 enum class RollupState { NONE, INITED, READY };
353 bool implicit_grouping; ///< True if aggregated but no GROUP BY
354
355 /**
356 At construction time, set if SELECT DISTINCT. May be reset to false
357 later, when we set up a temporary table operation that deduplicates for us.
358 */
360
361 /**
362 If we have the GROUP BY statement in the query,
363 but the group_list was emptied by optimizer, this
364 flag is true.
365 It happens when fields in the GROUP BY are from
366 constant table
367 */
369
370 /*
371 simple_xxxxx is set if ORDER/GROUP BY doesn't include any references
372 to other tables than the first non-constant table in the JOIN.
373 It's also set if ORDER/GROUP BY is empty.
374 Used for deciding for or against using a temporary table to compute
375 GROUP/ORDER BY.
376 */
377 bool simple_order{false};
378 bool simple_group{false};
379
380 /*
381 m_ordered_index_usage is set if an ordered index access
382 should be used instead of a filesort when computing
383 ORDER/GROUP BY.
384 */
385 enum {
386 ORDERED_INDEX_VOID, // No ordered index avail.
387 ORDERED_INDEX_GROUP_BY, // Use index for GROUP BY
388 ORDERED_INDEX_ORDER_BY // Use index for ORDER BY
389 } m_ordered_index_usage{ORDERED_INDEX_VOID};
390
391 /**
392 Is set if we have a GROUP BY and we have ORDER BY on a constant or when
393 sorting isn't required.
394 */
395 bool skip_sort_order{false};
396
397 /**
398 If true we need a temporary table on the result set before any
399 windowing steps, e.g. for DISTINCT or we have a query ORDER BY.
400 See details in JOIN::optimize
401 */
403
404 /// If JOIN has lateral derived tables (is set at start of planning)
405 bool has_lateral{false};
406
407 /// Used and updated by JOIN::make_join_plan() and optimize_keyuse()
409
410 /**
411 Array of pointers to lists of expressions.
412 Each list represents the SELECT list at a certain stage of execution,
413 and also contains necessary extras: expressions added for ORDER BY,
414 GROUP BY, window clauses, underlying items of split items.
415 This array is only used when the query makes use of tmp tables: after
416 writing to tmp table (e.g. for GROUP BY), if this write also does a
417 function's calculation (e.g. of SUM), after the write the function's value
418 is in a column of the tmp table. If a SELECT list expression is the SUM,
419 and we now want to read that materialized SUM and send it forward, a new
420 expression (Item_field type instead of Item_sum), is needed. The new
421 expressions are listed in JOIN::tmp_fields_list[x]; 'x' is a number
422 (REF_SLICE_).
423 @see JOIN::make_tmp_tables_info()
424 */
426
427 int error{0}; ///< set in optimize(), exec(), prepare_result()
428
429 /**
430 Incremented each time clear_hash_tables() is run, signaling to
431 HashJoinIterators that they cannot keep their hash tables anymore
432 (since outer references may have changed).
433 */
435
436 /**
437 ORDER BY and GROUP BY lists, to transform with prepare,optimize and exec
438 */
440
441 // Used so that AggregateIterator knows which items to signal when the rollup
442 // level changes. Obviously only used in the presence of rollup.
447
448 /**
449 Any window definitions
450 */
452
453 /**
454 True if a window requires a certain order of rows, which implies that any
455 order of rows coming out of the pre-window join will be disturbed.
456 */
457 bool m_windows_sort{false};
458
459 /// If we have set up tmp tables for windowing, @see make_tmp_tables_info
460 bool m_windowing_steps{false};
461
462 /**
463 Buffer to gather GROUP BY, ORDER BY and DISTINCT QEP details for EXPLAIN
464 */
466
467 /**
468 JOIN::having_cond is initially equal to query_block->having_cond, but may
469 later be changed by optimizations performed by JOIN.
470 The relationship between the JOIN::having_cond condition and the
471 associated variable query_block->having_value is so that
472 having_value can be:
473 - COND_UNDEF if a having clause was not specified in the query or
474 if it has not been optimized yet
475 - COND_TRUE if the having clause is always true, in which case
476 JOIN::having_cond is set to NULL.
477 - COND_FALSE if the having clause is impossible, in which case
478 JOIN::having_cond is set to NULL
479 - COND_OK otherwise, meaning that the having clause needs to be
480 further evaluated
481 All of the above also applies to the where_cond/query_block->cond_value
482 pair.
483 */
484 /**
485 Optimized WHERE clause item tree (valid for one single execution).
486 Used in JOIN execution if no tables. Otherwise, attached in pieces to
487 JOIN_TABs and then not used in JOIN execution.
488 Printed by EXPLAIN EXTENDED.
489 Initialized by Query_block::get_optimizable_conditions().
490 */
492 /**
493 Optimized HAVING clause item tree (valid for one single execution).
494 Used in JOIN execution, as last "row filtering" step. With one exception:
495 may be pushed to the JOIN_TABs of temporary tables used in DISTINCT /
496 GROUP BY (see JOIN::make_tmp_tables_info()); in that case having_cond is
497 set to NULL, but is first saved to having_for_explain so that EXPLAIN
498 EXTENDED can still print it.
499 Initialized by Query_block::get_optimizable_conditions().
500 */
502 Item *having_for_explain; ///< Saved optimized HAVING for EXPLAIN
503 /**
504 Pointer set to query_block->get_table_list() at the start of
505 optimization. May be changed (to NULL) only if optimize_aggregated_query()
506 optimizes tables away.
507 */
510 /*
511 Join tab to return to. Points to an element of join->join_tab array, or to
512 join->join_tab[-1].
513 This is used at execution stage to shortcut join enumeration. Currently
514 shortcutting is done to handle outer joins or handle semi-joins with
515 FirstMatch strategy.
516 */
518
519 /**
520 ref_items is an array of 4+ slices, each containing an array of Item
521 pointers. ref_items is used in different phases of query execution.
522 - slice 0 is initially the same as Query_block::base_ref_items, ie it is
523 the set of items referencing fields from base tables. During optimization
524 and execution it may be temporarily overwritten by slice 1-3.
525 - slice 1 is a representation of the used items when being read from
526 the first temporary table.
527 - slice 2 is a representation of the used items when being read from
528 the second temporary table.
529 - slice 3 is a copy of the original slice 0. It is created if
530 slice overwriting is necessary, and it is used to restore
531 original values in slice 0 after having been overwritten.
532 - slices 4 -> N are used by windowing: all the window's out tmp tables,
533
534 Two windows: 4: window 1's out table
535 5: window 2's out table
536
537 and so on.
538
539 Slice 0 is allocated for the lifetime of a statement, whereas slices 1-3
540 are associated with a single optimization. The size of slice 0 determines
541 the slice size used when allocating the other slices.
542 */
544 nullptr}; // cardinality: REF_SLICE_SAVED_BASE + 1 + #windows*2
545
546 /**
547 The slice currently stored in ref_items[0].
548 Used to restore the base ref_items slice from the "save" slice after it
549 has been overwritten by another slice (1-3).
550 */
552
553 /**
554 Used only if this query block is recursive. Contains count of
555 all executions of this recursive query block, since the last
556 this->reset().
557 */
559
560 /**
561 <> NULL if optimization has determined that execution will produce an
562 empty result before aggregation, contains a textual explanation on why
563 result is empty. Implicitly grouped queries may still produce an
564 aggregation row.
565 @todo - suggest to set to "Preparation determined that query is empty"
566 when Query_block::is_empty_query() is true.
567 */
568 const char *zero_result_cause{nullptr};
569
570 /**
571 True if, at this stage of processing, subquery materialization is allowed
572 for children subqueries of this JOIN (those in the SELECT list, in WHERE,
573 etc). If false, and we have to evaluate a subquery at this stage, then we
574 must choose EXISTS.
575 */
577 /**
578 True if plan search is allowed to use references to expressions outer to
579 this JOIN (for example may set up a 'ref' access looking up an outer
580 expression in the index, etc).
581 */
582 bool allow_outer_refs{false};
583
584 /* Temporary tables used to weed-out semi-join duplicates */
587 /* end of allocation caching storage */
588
589 /** Exec time only: true <=> current group has been sent */
590 bool group_sent{false};
591 /// If true, calculate found rows for this query block
592 bool calc_found_rows{false};
593
594 /**
595 This will force tmp table to NOT use index + update for group
596 operation as it'll cause [de]serialization for each json aggregated
597 value and is very ineffective (times worse).
598 Server should use filesort, or tmp table + filesort to resolve GROUP BY
599 with JSON aggregate functions.
600 */
602
603 /// True if plan is const, ie it will return zero or one rows.
604 bool plan_is_const() const { return const_tables == primary_tables; }
605
606 /**
607 True if plan contains one non-const primary table (ie not including
608 tables taking part in semi-join materialization).
609 */
611
612 bool optimize(bool finalize_access_paths);
613 void reset();
614 bool prepare_result();
615 void destroy();
616 bool alloc_func_list();
618 bool before_group_by, bool recompute = false);
619
620 /**
621 Overwrites one slice of ref_items with the contents of another slice.
622 In the normal case, dst and src have the same size().
623 However: the rollup slices may have smaller size than slice_sz.
624 */
625 void copy_ref_item_slice(uint dst_slice, uint src_slice) {
626 copy_ref_item_slice(ref_items[dst_slice], ref_items[src_slice]);
627 }
629 assert(dst_arr.size() >= src_arr.size());
630 void *dest = dst_arr.array();
631 const void *src = src_arr.array();
632 if (!src_arr.is_null())
633 memcpy(dest, src, src_arr.size() * src_arr.element_size());
634 }
635
636 /**
637 Allocate a ref_item slice, assume that slice size is in ref_items[0]
638
639 @param thd_arg thread handler
640 @param sliceno The slice number to allocate in JOIN::ref_items
641
642 @returns false if success, true if error
643 */
644 bool alloc_ref_item_slice(THD *thd_arg, int sliceno);
645
646 /**
647 Overwrite the base slice of ref_items with the slice supplied as argument.
648
649 @param sliceno number to overwrite the base slice with, must be 1-4 or
650 4 + windowno.
651 */
652 void set_ref_item_slice(uint sliceno) {
653 assert((int)sliceno >= 1);
654 if (current_ref_item_slice != sliceno) {
656 DBUG_PRINT("info", ("JOIN %p ref slice %u -> %u", this,
657 current_ref_item_slice, sliceno));
658 current_ref_item_slice = sliceno;
659 }
660 }
661
662 /// @note do also consider Switch_ref_item_slice
664
665 /**
666 Returns the clone of fields_list which is appropriate for evaluating
667 expressions at the current stage of execution; which stage is denoted by
668 the value of current_ref_item_slice.
669 */
671
672 bool optimize_rollup();
674 /**
675 Release memory and, if possible, the open tables held by this execution
676 plan (and nested plans). It's used to release some tables before
677 the end of execution in order to increase concurrency and reduce
678 memory consumption.
679 */
680 void join_free();
681 /** Cleanup this JOIN. Not a full cleanup. reusable? */
682 void cleanup();
683
684 bool clear_fields(table_map *save_nullinfo);
685 void restore_fields(table_map save_nullinfo);
686
687 /**
688 Return whether the caller should send a row even if the join
689 produced no rows if:
690 - there is an aggregate function (sum_func_count!=0), and
691 - the query is not grouped, and
692 - a possible HAVING clause evaluates to TRUE.
693
694 @note: if there is a having clause, it must be evaluated before
695 returning the row.
696 */
701 }
702
706 bool attach_join_conditions(plan_idx last_tab);
707
708 private:
709 bool attach_join_condition_to_nest(plan_idx first_inner, plan_idx last_tab,
710 Item *join_cond, bool is_sj_mat_cond);
711
712 public:
715 bool sort_before_group);
719 table_map plan_tables, uint idx) const;
720 bool clear_sj_tmp_tables();
723
724 void mark_const_table(JOIN_TAB *table, Key_use *key);
725 /// State of execution plan. Currently used only for EXPLAIN
727 NO_PLAN, ///< No plan is ready yet
728 ZERO_RESULT, ///< Zero result cause is set
729 NO_TABLES, ///< Plan has no tables
730 PLAN_READY ///< Plan is ready
731 };
732 /// See enum_plan_state
734 bool is_optimized() const { return optimized; }
735 void set_optimized() { optimized = true; }
736 bool is_executed() const { return executed; }
737 void set_executed() { executed = true; }
738
739 /**
740 Retrieve the cost model object to be used for this join.
741
742 @return Cost model object for the join
743 */
744
745 const Cost_model_server *cost_model() const;
746
747 /**
748 Check if FTS index only access is possible
749 */
750 bool fts_index_access(JOIN_TAB *tab);
751
753 /**
754 Propagate dependencies between tables due to outer join relations.
755
756 @returns false if success, true if error
757 */
759
760 /**
761 Handle offloading of query parts to the underlying engines, when
762 such is supported by their implementation.
763
764 @returns false if success, true if error
765 */
766 bool push_to_engines();
767
770
771 /**
772 If this query block was planned twice, once with and once without conditions
773 added by in2exists, changes the root access path to the one without
774 in2exists. If not (ie., there were never any such conditions in the first
775 place), does nothing.
776 */
778
779 /**
780 In the case of rollup (only): After the base slice list was made, we may
781 have modified the field list to add rollup group items and sum switchers,
782 but there may be Items with refs that refer to the base slice. This function
783 refreshes the base slice (and its copy, REF_SLICE_SAVED_BASE) with a fresh
784 copy of the list from “fields”.
785
786 When we get rid of slices entirely, we can get rid of this, too.
787 */
788 void refresh_base_slice();
789
790 /**
791 Whether this query block needs finalization (see
792 FinalizePlanForQueryBlock()) before it can be actually used.
793 This only happens when using the hypergraph join optimizer.
794 */
795 bool needs_finalize{false};
796
797 private:
798 bool optimized{false}; ///< flag to avoid double optimization in EXPLAIN
799
800 /**
801 Set by exec(), reset by reset(). Note that this needs to be set
802 _during_ the query (not only when it's done executing), or the
803 dynamic range optimizer will not understand which tables have been
804 read.
805 */
806 bool executed{false};
807
808 /// Final execution plan state. Currently used only for EXPLAIN
810
811 public:
812 /*
813 When join->select_count is set, tables will not be optimized away.
814 The call to records() will be delayed until the execution phase and
815 the counting will be done on an index of Optimizer's choice.
816 The index will be decided in find_shortest_key(), called from
817 optimize_aggregated_query().
818 */
819 bool select_count{false};
820
821 private:
822 /**
823 Create a temporary table to be used for processing DISTINCT/ORDER
824 BY/GROUP BY.
825
826 @note Will modify JOIN object wrt sort/group attributes
827
828 @param tab the JOIN_TAB object to attach created table to
829 @param tmp_table_fields List of items that will be used to define
830 column types of the table.
831 @param tmp_table_group Group key to use for temporary table, empty if none.
832 @param save_sum_fields If true, do not replace Item_sum items in
833 @c tmp_fields list with Item_field items referring
834 to fields in temporary table.
835
836 @returns false on success, true on failure
837 */
839 const mem_root_deque<Item *> &tmp_table_fields,
840 ORDER_with_src &tmp_table_group,
841 bool save_sum_fields);
842
843 /**
844 Optimize distinct when used on a subset of the tables.
845
846 E.g.,: SELECT DISTINCT t1.a FROM t1,t2 WHERE t1.b=t2.b
847 In this case we can stop scanning t2 when we have found one t1.a
848 */
849 void optimize_distinct();
850
851 /**
852 Function sets FT hints, initializes FT handlers and
853 checks if FT index can be used as covered.
854 */
855 bool optimize_fts_query();
856
858 /**
859 Initialize key dependencies for join tables.
860
861 TODO figure out necessity of this method. Current test
862 suite passed without this intialization.
863 */
865 JOIN_TAB *const tab_end = join_tab + tables;
866 for (JOIN_TAB *tab = join_tab; tab < tab_end; tab++)
867 tab->key_dependent = tab->dependent;
868 }
869
870 private:
871 void set_prefix_tables();
872 void cleanup_item_list(const mem_root_deque<Item *> &items) const;
874 bool make_join_plan();
875 bool init_planner_arrays();
879 bool estimate_rowcount();
880 void optimize_keyuse();
881 void set_semijoin_info();
882 /**
883 An utility function - apply heuristics and optimize access methods to tables.
884 @note Side effect - this function could set 'Impossible WHERE' zero
885 result.
886 */
888 void update_depend_map();
890 /**
891 Fill in outer join related info for the execution plan structure.
892
893 For each outer join operation left after simplification of the
894 original query the function set up the following pointers in the linear
895 structure join->join_tab representing the selected execution plan.
896 The first inner table t0 for the operation is set to refer to the last
897 inner table tk through the field t0->last_inner.
898 Any inner table ti for the operation are set to refer to the first
899 inner table ti->first_inner.
900 The first inner table t0 for the operation is set to refer to the
901 first inner table of the embedding outer join operation, if there is any,
902 through the field t0->first_upper.
903 The on expression for the outer join operation is attached to the
904 corresponding first inner table through the field t0->on_expr_ref.
905 Here ti are structures of the JOIN_TAB type.
906
907 EXAMPLE. For the query:
908 @code
909 SELECT * FROM t1
910 LEFT JOIN
911 (t2, t3 LEFT JOIN t4 ON t3.a=t4.a)
912 ON (t1.a=t2.a AND t1.b=t3.b)
913 WHERE t1.c > 5,
914 @endcode
915
916 given the execution plan with the table order t1,t2,t3,t4
917 is selected, the following references will be set;
918 t4->last_inner=[t4], t4->first_inner=[t4], t4->first_upper=[t2]
919 t2->last_inner=[t4], t2->first_inner=t3->first_inner=[t2],
920 on expression (t1.a=t2.a AND t1.b=t3.b) will be attached to
921 *t2->on_expr_ref, while t3.a=t4.a will be attached to *t4->on_expr_ref.
922
923 @note
924 The function assumes that the simplification procedure has been
925 already applied to the join query (see simplify_joins).
926 This function can be called only after the execution plan
927 has been chosen.
928 */
929 void make_outerjoin_info();
930
931 /**
932 Initialize ref access for all tables that use it.
933
934 @return False if success, True if error
935
936 @note We cannot setup fields used for ref access before we have sorted
937 the items within multiple equalities according to the final order of
938 the tables involved in the join operation. Currently, this occurs in
939 @see substitute_for_best_equal_field().
940 */
941 bool init_ref_access();
942 bool alloc_qep(uint n);
943 void unplug_join_tabs();
945 POSITION *inner_pos,
946 POSITION *sjm_pos);
947
948 bool add_having_as_tmp_table_cond(uint curr_tmp_table);
950 void set_plan_state(enum_plan_state plan_state_arg);
952 ORDER *remove_const(ORDER *first_order, Item *cond, bool change_list,
953 bool *simple_order, bool group_by);
954
955 /**
956 Check whether this is a subquery that can be evaluated by index look-ups.
957 If so, change subquery engine to subselect_indexsubquery_engine.
958
959 @retval 1 engine was changed
960 @retval 0 engine wasn't changed
961 @retval -1 OOM or other error
962 */
964
965 /**
966 Optimize DISTINCT, GROUP BY, ORDER BY clauses
967
968 @retval false ok
969 @retval true an error occurred
970 */
972
973 /**
974 Test if an index could be used to replace filesort for ORDER BY/GROUP BY
975
976 @details
977 Investigate whether we may use an ordered index as part of either
978 DISTINCT, GROUP BY or ORDER BY execution. An ordered index may be
979 used for only the first of any of these terms to be executed. This
980 is reflected in the order which we check for test_if_skip_sort_order()
981 below. However we do not check for DISTINCT here, as it would have
982 been transformed to a GROUP BY at this stage if it is a candidate for
983 ordered index optimization.
984 If a decision was made to use an ordered index, the availability
985 if such an access path is stored in 'm_ordered_index_usage' for later
986 use by 'execute' or 'explain'
987 */
988 void test_skip_sort();
989
991
992 /**
993 Convert the executor structures to a set of access paths, storing
994 the result in m_root_access_path.
995 */
996 void create_access_paths();
997
998 /**
999 Create access paths with the knowledge that there are going to be zero rows
1000 coming from tables (before aggregation); typically because we know that
1001 all of them would be filtered away by WHERE (e.g. SELECT * FROM t1
1002 WHERE 1=2). This will normally yield no output rows, but if we have implicit
1003 aggregation, it might yield a single one.
1004 */
1006
1008
1009 /** @{ Helpers for create_access_paths. */
1013 /** @} */
1014
1015 /**
1016 An access path you can read from to get all records for this query
1017 (after you create an iterator from it).
1018 */
1020
1021 /**
1022 If this query block contains conditions synthesized during IN-to-EXISTS
1023 conversion: A second query plan with all such conditions removed.
1024 See comments in JOIN::optimize().
1025 */
1027};
1028
1029/**
1030 Use this in a function which depends on best_ref listing tables in the
1031 final join order. If 'tables==0', one is not expected to consult best_ref
1032 cells, and best_ref may not even have been allocated.
1033*/
1034#define ASSERT_BEST_REF_IN_JOIN_ORDER(join) \
1035 do { \
1036 assert((join)->tables == 0 || ((join)->best_ref && !(join)->join_tab)); \
1037 } while (0)
1038
1039/**
1040 RAII class to ease the temporary switching to a different slice of
1041 the ref item array.
1042*/
1046
1047 public:
1049 : join(join_arg), saved(join->get_ref_item_slice()) {
1050 if (!join->ref_items[new_v].is_null()) join->set_ref_item_slice(new_v);
1051 }
1053};
1054
1055bool uses_index_fields_only(Item *item, TABLE *tbl, uint keyno,
1056 bool other_tbls_ok);
1057bool remove_eq_conds(THD *thd, Item *cond, Item **retcond,
1058 Item::cond_result *cond_value);
1059bool optimize_cond(THD *thd, Item **conds, COND_EQUAL **cond_equal,
1061 Item::cond_result *cond_value);
1063 COND_EQUAL *cond_equal,
1064 JOIN_TAB **table_join_idx);
1065bool build_equal_items(THD *thd, Item *cond, Item **retcond,
1066 COND_EQUAL *inherited, bool do_inherit,
1068 COND_EQUAL **cond_equal_ref);
1072 THD *thd, uint keyparts, Item_field **fields,
1073 const mem_root_deque<Item *> &outer_exprs);
1074Item_field *get_best_field(Item_field *item_field, COND_EQUAL *cond_equal);
1075Item *make_cond_for_table(THD *thd, Item *cond, table_map tables,
1076 table_map used_table, bool exclude_expensive_cond);
1078 uint first_unused);
1079
1080/**
1081 Create an order list that consists of all non-const fields and items.
1082 This is usable for e.g. converting DISTINCT into GROUP or ORDER BY.
1083 Is ref_item_array is non-null (is_null() returns false), the items
1084 will point into the slice given by it. Otherwise, it points directly
1085 into *fields (this is the only reason why fields is not const).
1086
1087 Try to put the items in "order_list" first, to allow one to optimize away
1088 a later ORDER BY.
1089 */
1091 ORDER *order_list,
1092 mem_root_deque<Item *> *fields,
1093 bool skip_aggregates,
1094 bool convert_bit_fields_to_long,
1095 bool *all_order_by_fields_used);
1096
1097/**
1098 Returns true if arguments are a temporal Field having no date,
1099 part and a temporal expression having a date part.
1100 @param f Field
1101 @param v Expression
1102 */
1103inline bool field_time_cmp_date(const Field *f, const Item *v) {
1104 const enum_field_types ft = f->type();
1105 return is_temporal_type(ft) && !is_temporal_type_with_date(ft) &&
1107}
1108
1109bool substitute_gc(THD *thd, Query_block *query_block, Item *where_cond,
1110 ORDER *group_list, ORDER *order);
1111
1112/**
1113 This class restores a table_map object to its original value
1114 when '*this' is destroyed.
1115 */
1117 /** The location to be restored.*/
1119 /** The original value to restore.*/
1121
1122 public:
1123 /**
1124 Constructor.
1125 @param map The table map that we wish to restore.
1126 */
1128 : m_location(map), m_saved_value(*map) {}
1129
1130 // This class is not intended to be copied.
1133
1136 void assert_unchanged() const { assert(*m_location == m_saved_value); }
1137};
1138
1139/**
1140 Estimates how many times a subquery will be executed as part of a
1141 query execution. If it is a cacheable subquery, the estimate tells
1142 how many times the subquery will be executed if it is not cached.
1143
1144 @param[in] subquery the Item that represents the subquery
1145 @param[in,out] trace optimizer trace context
1146
1147 @return the number of times the subquery is expected to be executed
1148*/
1149double calculate_subquery_executions(const Item_subselect *subquery,
1150 Opt_trace_context *trace);
1151
1152extern const char *antijoin_null_cond;
1153
1154/**
1155 Checks if an Item, which is constant for execution, can be evaluated during
1156 optimization. It cannot be evaluated if it contains a subquery and the
1157 OPTION_NO_SUBQUERY_DURING_OPTIMIZATION query option is active.
1158
1159 @param item the Item to check
1160 @param select the query block that contains the Item
1161 @return false if this Item contains a subquery and subqueries cannot be
1162 evaluated during optimization, or true otherwise
1163*/
1164bool evaluate_during_optimization(const Item *item, const Query_block *select);
1165
1166/**
1167 Find the multiple equality predicate containing a field.
1168
1169 The function retrieves the multiple equalities accessed through
1170 the cond_equal structure from current level and up looking for
1171 an equality containing a field. It stops retrieval as soon as the equality
1172 is found and set up inherited_fl to true if it's found on upper levels.
1173
1174 @param cond_equal multiple equalities to search in
1175 @param item_field field to look for
1176 @param[out] inherited_fl set up to true if multiple equality is found
1177 on upper levels (not on current level of
1178 cond_equal)
1179
1180 @return
1181 - Item_equal for the found multiple equality predicate if a success;
1182 - nullptr otherwise.
1183*/
1185 const Item_field *item_field, bool *inherited_fl);
1186
1187/**
1188 Find an artificial cap for ref access. This is mostly a crutch to mitigate
1189 that we don't estimate the cache effects of ref accesses properly
1190 (ie., normally, if we do many, they will hit cache instead of being
1191 separate seeks). Given to find_cost_for_ref().
1192 */
1193double find_worst_seeks(const TABLE *table, double num_rows,
1194 double table_scan_cost);
1195
1196/**
1197 Whether a ref lookup of “right_item” on “field” will give an exact
1198 comparison in all cases, ie., one can remove any further checks on
1199 field = right_item. If not, there may be false positives, and one
1200 needs to keep the comparison after the ref lookup.
1201 */
1202bool ref_lookup_subsumes_comparison(Field *field, Item *right_item);
1203
1204#endif /* SQL_OPTIMIZER_INCLUDED */
bool is_null() const
Definition: sql_array.h:134
Element_type * array() const
Definition: sql_array.h:142
size_t size() const
Definition: sql_array.h:131
size_t element_size() const
Definition: sql_array.h:130
Definition: item_cmpfunc.h:2633
API for getting cost estimates for server operations that are not directly related to a table object.
Definition: opt_costmodel.h:51
Definition: opt_explain_format.h:448
Definition: field.h:573
virtual enum_field_types type() const =0
Definition: item_cmpfunc.h:2495
Definition: item.h:4043
Definition: item_subselect.h:79
Class Item_sum is the base class used for special expressions that SQL calls 'set functions'.
Definition: item_sum.h:398
Base class that is used to represent any kind of expression in a relational query.
Definition: item.h:802
bool is_temporal_with_date() const
Definition: item.h:3018
cond_result
Definition: item.h:871
@ COND_FALSE
Definition: item.h:871
Query optimization plan node.
Definition: sql_select.h:598
Definition: sql_optimizer.h:125
const Cost_model_server * cost_model() const
Retrieve the cost model object to be used for this join.
Definition: sql_optimizer.cc:11095
bool skip_sort_order
Is set if we have a GROUP BY and we have ORDER BY on a constant or when sorting isn't required.
Definition: sql_optimizer.h:395
bool attach_join_condition_to_nest(plan_idx first_inner, plan_idx last_tab, Item *join_cond, bool is_sj_mat_cond)
Helper for JOIN::attach_join_conditions().
Definition: sql_optimizer.cc:8448
void set_root_access_path(AccessPath *path)
Definition: sql_optimizer.h:769
bool calc_found_rows
If true, calculate found rows for this query block.
Definition: sql_optimizer.h:592
bool plan_is_single_table()
True if plan contains one non-const primary table (ie not including tables taking part in semi-join m...
Definition: sql_optimizer.h:610
void mark_const_table(JOIN_TAB *table, Key_use *key)
Move const tables first in the position array.
Definition: sql_optimizer.cc:8279
JOIN_TAB * join_tab
Optimal query execution plan.
Definition: sql_optimizer.h:146
ha_rows fetch_limit
Used to fetch no more than given amount of rows per one fetch operation of server side cursor.
Definition: sql_optimizer.h:297
Item_sum ** sum_funcs
Definition: sql_optimizer.h:341
List< Cached_item > group_fields
Definition: sql_optimizer.h:335
bool m_windows_sort
True if a window requires a certain order of rows, which implies that any order of rows coming out of...
Definition: sql_optimizer.h:457
MYSQL_LOCK * lock
Definition: sql_optimizer.h:349
bool executed
Set by exec(), reset by reset().
Definition: sql_optimizer.h:806
QEP_TAB * qep_tab
Array of QEP_TABs.
Definition: sql_optimizer.h:148
bool send_row_on_empty_set() const
Return whether the caller should send a row even if the join produced no rows if:
Definition: sql_optimizer.h:697
ha_rows found_records
Definition: sql_optimizer.h:283
uint recursive_iteration_count
Used only if this query block is recursive.
Definition: sql_optimizer.h:558
void copy_ref_item_slice(Ref_item_array dst_arr, Ref_item_array src_arr)
Definition: sql_optimizer.h:628
bool child_subquery_can_materialize
True if, at this stage of processing, subquery materialization is allowed for children subqueries of ...
Definition: sql_optimizer.h:576
Prealloced_array< Item_rollup_group_item *, 4 > rollup_group_items
Definition: sql_optimizer.h:443
COND_EQUAL * cond_equal
Definition: sql_optimizer.h:509
JOIN_TAB ** map2table
mapping between table indexes and JOIN_TABs
Definition: sql_optimizer.h:158
ha_rows m_select_limit
Definition: sql_optimizer.h:287
POSITION * positions
Definition: sql_optimizer.h:309
uint current_ref_item_slice
The slice currently stored in ref_items[0].
Definition: sql_optimizer.h:551
bool is_executed() const
Definition: sql_optimizer.h:736
uint tables
Before plan has been created, "tables" denote number of input tables in the query block and "primary_...
Definition: sql_optimizer.h:207
bool has_lateral
If JOIN has lateral derived tables (is set at start of planning)
Definition: sql_optimizer.h:405
bool need_tmp_before_win
If true we need a temporary table on the result set before any windowing steps, e....
Definition: sql_optimizer.h:402
Prealloced_array< Item_rollup_sum_switcher *, 4 > rollup_sums
Definition: sql_optimizer.h:445
uint tmp_tables
Number of temporary tables used by query.
Definition: sql_optimizer.h:210
int error
set in optimize(), exec(), prepare_result()
Definition: sql_optimizer.h:427
bool plan_is_const() const
True if plan is const, ie it will return zero or one rows.
Definition: sql_optimizer.h:604
table_map const_table_map
Set of tables found to be const.
Definition: sql_optimizer.h:234
Prealloced_array< TemporaryTableToCleanup, 1 > temp_tables
Definition: sql_optimizer.h:176
Query_block *const query_block
Query block that is optimized and executed using this JOIN.
Definition: sql_optimizer.h:137
bool select_distinct
At construction time, set if SELECT DISTINCT.
Definition: sql_optimizer.h:359
RollupState
Definition: sql_optimizer.h:351
List< TABLE > sj_tmp_tables
Definition: sql_optimizer.h:585
table_map found_const_table_map
Const tables which are either:
Definition: sql_optimizer.h:241
bool simple_order
Definition: sql_optimizer.h:377
void set_executed()
Definition: sql_optimizer.h:737
List< Window > m_windows
Any window definitions.
Definition: sql_optimizer.h:451
Explain_format_flags explain_flags
Buffer to gather GROUP BY, ORDER BY and DISTINCT QEP details for EXPLAIN.
Definition: sql_optimizer.h:465
mem_root_deque< Item * > * tmp_fields
Array of pointers to lists of expressions.
Definition: sql_optimizer.h:425
uint const_tables
Number of primary tables deemed constant.
Definition: sql_optimizer.h:209
Prealloced_array< Filesort *, 1 > filesorts_to_cleanup
Definition: sql_optimizer.h:181
ha_rows examined_rows
Definition: sql_optimizer.h:284
ha_rows row_limit
Definition: sql_optimizer.h:285
bool allow_outer_refs
True if plan search is allowed to use references to expressions outer to this JOIN (for example may s...
Definition: sql_optimizer.h:582
JOIN_TAB ** best_ref
Array of plan operators representing the current (partial) best plan.
Definition: sql_optimizer.h:156
Item * having_for_explain
Saved optimized HAVING for EXPLAIN.
Definition: sql_optimizer.h:502
RollupState rollup_state
Definition: sql_optimizer.h:352
AccessPath * root_access_path() const
Definition: sql_optimizer.h:768
ha_rows send_records
Definition: sql_optimizer.h:282
Override_executor_func override_executor_func
Definition: sql_optimizer.h:318
plan_idx return_tab
Definition: sql_optimizer.h:517
enum_plan_state plan_state
Final execution plan state. Currently used only for EXPLAIN.
Definition: sql_optimizer.h:809
Item * having_cond
Optimized HAVING clause item tree (valid for one single execution).
Definition: sql_optimizer.h:501
void make_outerjoin_info()
Fill in outer join related info for the execution plan structure.
Definition: sql_optimizer.cc:8308
TABLE_LIST * tables_list
Pointer set to query_block->get_table_list() at the start of optimization.
Definition: sql_optimizer.h:508
mem_root_deque< Item * > * fields
Definition: sql_optimizer.h:334
Temp_table_param tmp_table_param
Describes a temporary table.
Definition: sql_optimizer.h:348
bool select_count
Definition: sql_optimizer.h:819
@ ORDERED_INDEX_GROUP_BY
Definition: sql_optimizer.h:387
@ ORDERED_INDEX_VOID
Definition: sql_optimizer.h:386
@ ORDERED_INDEX_ORDER_BY
Definition: sql_optimizer.h:388
bool m_windowing_steps
If we have set up tmp tables for windowing,.
Definition: sql_optimizer.h:460
bool fts_index_access(JOIN_TAB *tab)
Check if FTS index only access is possible.
Definition: sql_optimizer.cc:10612
void optimize_keyuse()
Update some values in keyuse for faster choose_table_order() loop.
Definition: sql_optimizer.cc:10514
bool with_json_agg
This will force tmp table to NOT use index + update for group operation as it'll cause [de]serializat...
Definition: sql_optimizer.h:601
uint send_group_parts
Definition: sql_optimizer.h:211
bool finalize_table_conditions()
Remove redundant predicates and cache constant expressions.
Definition: sql_optimizer.cc:8902
AccessPath * m_root_access_path_no_in2exists
If this query block contains conditions synthesized during IN-to-EXISTS conversion: A second query pl...
Definition: sql_optimizer.h:1026
ORDER_with_src group_list
Definition: sql_optimizer.h:439
double sort_cost
Expected cost of filesort.
Definition: sql_optimizer.h:331
bool generate_derived_keys()
Add keys to derived tables'/views' result tables in a list.
Definition: sql_optimizer.cc:8979
bool optimize_fts_query()
Function sets FT hints, initializes FT handlers and checks if FT index can be used as covered.
Definition: sql_optimizer.cc:10553
enum_plan_state
State of execution plan. Currently used only for EXPLAIN.
Definition: sql_optimizer.h:726
@ NO_TABLES
Plan has no tables.
Definition: sql_optimizer.h:729
@ NO_PLAN
No plan is ready yet.
Definition: sql_optimizer.h:727
@ ZERO_RESULT
Zero result cause is set.
Definition: sql_optimizer.h:728
@ PLAN_READY
Plan is ready.
Definition: sql_optimizer.h:730
Key_use_array keyuse_array
Used and updated by JOIN::make_join_plan() and optimize_keyuse()
Definition: sql_optimizer.h:408
bool group_sent
Exec time only: true <=> current group has been sent.
Definition: sql_optimizer.h:590
bool needs_finalize
Whether this query block needs finalization (see FinalizePlanForQueryBlock()) before it can be actual...
Definition: sql_optimizer.h:795
void init_key_dependencies()
Initialize key dependencies for join tables.
Definition: sql_optimizer.h:864
void set_ref_item_slice(uint sliceno)
Overwrite the base slice of ref_items with the slice supplied as argument.
Definition: sql_optimizer.h:652
List< Cached_item > group_fields_cache
Definition: sql_optimizer.h:336
bool streaming_aggregation
Indicates that the data will be aggregated (typically GROUP BY), and that it is already processed in ...
Definition: sql_optimizer.h:227
void set_optimized()
Definition: sql_optimizer.h:735
uint primary_tables
Number of primary input tables in query block.
Definition: sql_optimizer.h:208
bool optimize_rollup()
Optimize rollup specification.
Definition: sql_optimizer.cc:11052
THD *const thd
Thread handler.
Definition: sql_optimizer.h:139
table_map all_table_map
Set of tables contained in query.
Definition: sql_optimizer.h:233
bool attach_join_conditions(plan_idx last_tab)
Attach outer join conditions to generated table conditions in an optimal way.
Definition: sql_optimizer.cc:8559
bool decide_subquery_strategy()
Decides between EXISTS and materialization; performs last steps to set up the chosen strategy.
Definition: sql_optimizer.cc:10766
List< Semijoin_mat_exec > sjm_exec_list
Definition: sql_optimizer.h:586
JOIN(const JOIN &rhs)=delete
TABLE * sort_by_table
Definition: sql_optimizer.h:164
Ref_item_array * ref_items
ref_items is an array of 4+ slices, each containing an array of Item pointers.
Definition: sql_optimizer.h:543
bool do_send_rows
If true, send produced rows using query_result.
Definition: sql_optimizer.h:231
double windowing_cost
Expected cost of windowing;.
Definition: sql_optimizer.h:333
enum_plan_state get_plan_state() const
See enum_plan_state.
Definition: sql_optimizer.h:733
JOIN & operator=(const JOIN &rhs)=delete
ORDER_with_src order
ORDER BY and GROUP BY lists, to transform with prepare,optimize and exec.
Definition: sql_optimizer.h:439
bool group_optimized_away
If we have the GROUP BY statement in the query, but the group_list was emptied by optimizer,...
Definition: sql_optimizer.h:368
double best_read
The cost of best complete join plan found so far during optimization, after optimization phase - cost...
Definition: sql_optimizer.h:325
ORDER * remove_const(ORDER *first_order, Item *cond, bool change_list, bool *simple_order, bool group_by)
Remove all constants and check if ORDER only contains simple expressions.
Definition: sql_optimizer.cc:9886
enum JOIN::@171 ORDERED_INDEX_VOID
bool implicit_grouping
True if aggregated but no GROUP BY.
Definition: sql_optimizer.h:353
POSITION * best_positions
This is the result of join optimization.
Definition: sql_optimizer.h:304
void finalize_derived_keys()
For each materialized derived table/view, informs every TABLE of the key it will (not) use,...
Definition: sql_optimizer.cc:8999
bool optimized
flag to avoid double optimization in EXPLAIN
Definition: sql_optimizer.h:798
bool compare_costs_of_subquery_strategies(Subquery_strategy *method)
Tells what is the cheapest between IN->EXISTS and subquery materialization, in terms of cost,...
Definition: sql_optimizer.cc:10827
bool is_optimized() const
Definition: sql_optimizer.h:734
const char * zero_result_cause
<> NULL if optimization has determined that execution will produce an empty result before aggregation...
Definition: sql_optimizer.h:568
Query_expression * query_expression() const
Query expression referring this query block.
Definition: sql_optimizer.h:132
mem_root_deque< Item * > * get_current_fields()
Returns the clone of fields_list which is appropriate for evaluating expressions at the current stage...
Definition: sql_optimizer.cc:11089
bool(*)(JOIN *, Query_result *) Override_executor_func
A hook that secondary storage engines can use to override the executor completely.
Definition: sql_optimizer.h:317
void clear_hash_tables()
Definition: sql_optimizer.h:722
uint get_ref_item_slice() const
Definition: sql_optimizer.h:663
List< Cached_item > semijoin_deduplication_fields
Definition: sql_optimizer.h:339
bool grouped
If query contains GROUP BY clause.
Definition: sql_optimizer.h:229
void refine_best_rowcount()
Refine the best_rowcount estimation based on what happens after tables have been joined: LIMIT and ty...
Definition: sql_optimizer.cc:11063
AccessPath * m_root_access_path
An access path you can read from to get all records for this query (after you create an iterator from...
Definition: sql_optimizer.h:1019
ha_rows best_rowcount
The estimated row count of the plan with best read time (see above).
Definition: sql_optimizer.h:329
Item * where_cond
JOIN::having_cond is initially equal to query_block->having_cond, but may later be changed by optimiz...
Definition: sql_optimizer.h:491
bool simple_group
Definition: sql_optimizer.h:378
uint64_t hash_table_generation
Incremented each time clear_hash_tables() is run, signaling to HashJoinIterators that they cannot kee...
Definition: sql_optimizer.h:434
table_map deps_of_remaining_lateral_derived_tables
This is the bitmap of all tables which are dependencies of lateral derived tables which are not (yet)...
Definition: sql_optimizer.h:279
void copy_ref_item_slice(uint dst_slice, uint src_slice)
Overwrites one slice of ref_items with the contents of another slice.
Definition: sql_optimizer.h:625
A Key_use represents an equality predicate of the form (table.column = val), where the column is inde...
Definition: sql_select.h:173
Definition: sql_list.h:433
A typesafe replacement for DYNAMIC_ARRAY.
Definition: mem_root_array.h:421
Wrapper for ORDER* pointer to trace origins of ORDER list.
Definition: sql_optimizer.h:95
bool empty() const
Definition: sql_optimizer.h:111
int get_flags() const
Definition: sql_optimizer.h:119
void clean()
Definition: sql_optimizer.h:113
ORDER * order
ORDER expression that we are wrapping with this class.
Definition: sql_optimizer.h:97
ORDER_with_src()
Definition: sql_optimizer.h:104
Explain_sort_clause src
origin of order list
Definition: sql_optimizer.h:98
int flags
bitmap of Explain_sort_property
Definition: sql_optimizer.h:101
ORDER_with_src(ORDER *order_arg, Explain_sort_clause src_arg)
Definition: sql_optimizer.h:106
A per-session context which is always available at any point of execution, because in practice it's a...
Definition: opt_trace_context.h:89
A typesafe replacement for DYNAMIC_ARRAY.
Definition: prealloced_array.h:70
Definition: sql_executor.h:259
enum_op_type
Definition: sql_executor.h:406
This class represents a query block, aka a query specification, which is a query consisting of a SELE...
Definition: sql_lex.h:1124
Item::cond_result having_value
Definition: sql_lex.h:2003
Query_expression * master_query_expression() const
Definition: sql_lex.h:1200
This class represents a query expression (one query block or several query blocks combined with UNION...
Definition: sql_lex.h:629
Definition: query_result.h:55
RAII class to ease the temporary switching to a different slice of the ref item array.
Definition: sql_optimizer.h:1043
Switch_ref_item_slice(JOIN *join_arg, uint new_v)
Definition: sql_optimizer.h:1048
uint saved
Definition: sql_optimizer.h:1045
JOIN * join
Definition: sql_optimizer.h:1044
~Switch_ref_item_slice()
Definition: sql_optimizer.h:1052
For each client connection we create a separate thread with THD serving as a thread/connection descri...
Definition: sql_class.h:945
This class restores a table_map object to its original value when '*this' is destroyed.
Definition: sql_optimizer.h:1116
Table_map_restorer(table_map *map)
Constructor.
Definition: sql_optimizer.h:1127
Table_map_restorer & operator=(const Table_map_restorer &)=delete
table_map *const m_location
The location to be restored.
Definition: sql_optimizer.h:1118
~Table_map_restorer()
Definition: sql_optimizer.h:1134
const table_map m_saved_value
The original value to restore.
Definition: sql_optimizer.h:1120
void restore()
Definition: sql_optimizer.h:1135
void assert_unchanged() const
Definition: sql_optimizer.h:1136
Table_map_restorer(const Table_map_restorer &)=delete
Object containing parameters used when creating and using temporary tables.
Definition: temp_table_param.h:98
uint sum_func_count
Number of fields in the query that have aggregate functions.
Definition: temp_table_param.h:135
Represents the (explicit) window of a SQL 2003 section 7.11 <window clause>, or the implicit (inlined...
Definition: window.h:104
A (partial) implementation of std::deque allocating its blocks on a MEM_ROOT.
Definition: mem_root_deque.h:109
bool is_temporal_type(enum_field_types type)
Tests if field type is temporal, i.e.
Definition: field_common_properties.h:114
bool is_temporal_type_with_date(enum_field_types type)
Tests if field type is temporal and has date part, i.e.
Definition: field_common_properties.h:155
This file contains the field type.
enum_field_types
Column types for MySQL.
Definition: field_types.h:57
void optimize_distinct()
Optimize distinct when used on a subset of the tables.
Definition: sql_executor.cc:344
AccessPath * create_root_access_path_for_join()
Definition: sql_executor.cc:2821
void restore_fields(table_map save_nullinfo)
Restore all result fields for all tables specified in save_nullinfo.
Definition: sql_executor.cc:4429
bool create_intermediate_table(QEP_TAB *tab, const mem_root_deque< Item * > &tmp_table_fields, ORDER_with_src &tmp_table_group, bool save_sum_fields)
Create a temporary table to be used for processing DISTINCT/ORDER BY/GROUP BY.
Definition: sql_executor.cc:176
AccessPath * attach_access_paths_for_having_and_limit(AccessPath *path)
Definition: sql_executor.cc:3155
QEP_TAB::enum_op_type get_end_select_func()
Definition: sql_executor.cc:572
AccessPath * attach_access_path_for_delete(AccessPath *path)
Definition: sql_executor.cc:2775
void create_access_paths()
Convert the executor structures to a set of access paths, storing the result in m_root_access_path.
Definition: sql_executor.cc:2791
void create_access_paths_for_index_subquery()
Definition: sql_executor.cc:3188
bool clear_fields(table_map *save_nullinfo)
Set all column values from all input tables to NULL.
Definition: sql_executor.cc:4408
bool clear_corr_derived_tmp_tables()
Empties all correlated materialized derived tables.
Definition: sql_select.cc:1592
Item_equal * find_item_equal(COND_EQUAL *cond_equal, const Item_field *item_field, bool *inherited_fl)
Find the multiple equality predicate containing a field.
Definition: sql_optimizer.cc:3579
uint build_bitmap_for_nested_joins(mem_root_deque< TABLE_LIST * > *join_list, uint first_unused)
Assign each nested join structure a bit in nested_join_map.
Definition: sql_optimizer.cc:4859
bool alloc_func_list()
Make an array of pointers to sum_functions to speed up sum_func calculation.
Definition: sql_select.cc:3896
Item_field * get_best_field(Item_field *item_field, COND_EQUAL *cond_equal)
Get the best field substitution for a given field.
Definition: sql_optimizer.cc:3612
void update_sargable_from_const(SARGABLE_PARAM *sargables)
Update info on indexes that can be used for search lookups as reading const tables may has added new ...
Definition: sql_optimizer.cc:5708
bool add_sorting_to_table(uint idx, ORDER_with_src *order, bool sort_before_group)
Add Filesort object to the given table to sort if with filesort.
Definition: sql_select.cc:4809
bool clear_sj_tmp_tables()
Remove all rows from all temp tables used by NL-semijoin runtime.
Definition: sql_select.cc:1582
bool alloc_qep(uint n)
Definition: sql_optimizer.cc:1262
void change_to_access_path_without_in2exists()
If this query block was planned twice, once with and once without conditions added by in2exists,...
Definition: sql_optimizer.cc:1062
void unplug_join_tabs()
Definition: sql_select.cc:4781
bool push_to_engines()
Handle offloading of query parts to the underlying engines, when such is supported by their implement...
Definition: sql_optimizer.cc:1097
bool make_tmp_tables_info()
Init tmp tables usage info.
Definition: sql_select.cc:4179
bool make_join_plan()
Calculate best possible join order and initialize the join structure.
Definition: sql_optimizer.cc:5141
void set_semijoin_embedding()
Set semi-join embedding join nest pointers.
Definition: sql_optimizer.cc:5856
bool build_equal_items(THD *thd, Item *cond, Item **retcond, COND_EQUAL *inherited, bool do_inherit, mem_root_deque< TABLE_LIST * > *join_list, COND_EQUAL **cond_equal_ref)
Build multiple equalities for a WHERE condition and all join conditions that inherit these multiple e...
Definition: sql_optimizer.cc:4301
bool optimize_distinct_group_order()
Optimize DISTINCT, GROUP BY, ORDER BY clauses.
Definition: sql_optimizer.cc:1409
JOIN(THD *thd_arg, Query_block *select)
Definition: sql_optimizer.cc:157
table_map calculate_deps_of_remaining_lateral_derived_tables(table_map plan_tables, uint idx) const
Finds the dependencies of the remaining lateral derived tables.
Definition: sql_optimizer.cc:3198
void set_prefix_tables()
Assign set of available (prefix) tables to all tables in query block.
Definition: sql_optimizer.cc:5034
void cleanup()
Cleanup this JOIN.
Definition: sql_select.cc:3534
bool uses_index_fields_only(Item *item, TABLE *tbl, uint keyno, bool other_tbls_ok)
Check if given expression only uses fields covered by index keyno in the table tbl.
Definition: sql_optimizer.cc:6309
void test_skip_sort()
Test if an index could be used to replace filesort for ORDER BY/GROUP BY.
Definition: sql_optimizer.cc:1602
void create_access_paths_for_zero_rows()
Create access paths with the knowledge that there are going to be zero rows coming from tables (befor...
Definition: sql_optimizer.cc:1068
bool propagate_dependencies()
Propagate dependencies between tables due to outer join relations.
Definition: sql_optimizer.cc:5406
void adjust_access_methods()
An utility function - apply heuristics and optimize access methods to tables.
Definition: sql_optimizer.cc:2856
bool estimate_rowcount()
Estimate the number of matched rows for each joined table.
Definition: sql_optimizer.cc:5744
bool prune_table_partitions()
Prune partitions for all tables of a join (query block).
Definition: sql_optimizer.cc:2708
void refresh_base_slice()
In the case of rollup (only): After the base slice list was made, we may have modified the field list...
Definition: sql_select.cc:4756
bool alloc_ref_item_slice(THD *thd_arg, int sliceno)
Allocate a ref_item slice, assume that slice size is in ref_items[0].
Definition: sql_optimizer.cc:197
bool setup_semijoin_materialized_table(JOIN_TAB *tab, uint tableno, POSITION *inner_pos, POSITION *sjm_pos)
Setup the materialized table for a semi-join nest.
Definition: sql_select.cc:2883
void join_free()
Release memory and, if possible, the open tables held by this execution plan (and nested plans).
Definition: sql_select.cc:3464
bool make_sum_func_list(const mem_root_deque< Item * > &fields, bool before_group_by, bool recompute=false)
Initialize 'sum_funcs' array with all Item_sum objects.
Definition: sql_select.cc:3944
bool extract_func_dependent_tables()
Extract const tables based on functional dependencies.
Definition: sql_optimizer.cc:5551
bool init_planner_arrays()
Initialize scratch arrays for the join order optimization.
Definition: sql_optimizer.cc:5279
bool substitute_gc(THD *thd, Query_block *query_block, Item *where_cond, ORDER *group_list, ORDER *order)
Substitute all expressions in the WHERE condition and ORDER/GROUP lists that match generated columns ...
Definition: sql_optimizer.cc:1143
void set_semijoin_info()
Set the first_sj_inner_tab and last_sj_inner_tab fields for all tables inside the semijoin nests of t...
Definition: sql_select.cc:2026
bool prepare_result()
Prepare join result.
Definition: sql_select.cc:1676
void destroy()
Clean up and destroy join object.
Definition: sql_select.cc:1694
bool add_having_as_tmp_table_cond(uint curr_tmp_table)
Add having condition as a filter condition, which is applied when reading from the temp table.
Definition: sql_select.cc:4024
Item * substitute_for_best_equal_field(THD *thd, Item *cond, COND_EQUAL *cond_equal, JOIN_TAB **table_join_idx)
Substitute every field reference in a condition by the best equal field and eliminate all multiple eq...
Definition: sql_optimizer.cc:4607
double find_worst_seeks(const TABLE *table, double num_rows, double table_scan_cost)
Find an artificial cap for ref access.
Definition: sql_optimizer.cc:5724
const char * antijoin_null_cond
Definition: sql_optimizer.cc:115
bool alloc_indirection_slices()
Definition: sql_optimizer.cc:207
void reset()
Reset the state of this join object so that it is ready for a new execution.
Definition: sql_select.cc:1613
bool optimize(bool finalize_access_paths)
Optimizes one query block into a query execution plan (QEP.)
Definition: sql_optimizer.cc:281
bool init_ref_access()
Initialize ref access for all tables that use it.
Definition: sql_select.cc:2003
bool get_best_combination()
Set up JOIN_TAB structs according to the picked join order in best_positions.
Definition: sql_optimizer.cc:2974
bool extract_const_tables()
Extract const tables based on row counts.
Definition: sql_optimizer.cc:5457
bool update_equalities_for_sjm()
Update equalities and keyuse references after semi-join materialization strategy is chosen.
Definition: sql_optimizer.cc:4970
void set_plan_state(enum_plan_state plan_state_arg)
Sets the plan's state of the JOIN.
Definition: sql_optimizer.cc:1234
void cleanup_item_list(const mem_root_deque< Item * > &items) const
Definition: sql_select.cc:1788
int replace_index_subquery()
Check whether this is a subquery that can be evaluated by index look-ups.
Definition: sql_optimizer.cc:1342
void update_depend_map()
Update the dependency map for the tables.
Definition: sql_optimizer.cc:4901
Subquery_strategy
Strategy which will be used to handle this subquery: flattening to a semi-join, conversion to a deriv...
Definition: item_subselect.h:390
This file follows Google coding style, except for the name MEM_ROOT (which is kept for historical rea...
This file includes constants used by all storage engines.
my_off_t ha_rows
Definition: my_base.h:1139
#define HA_POS_ERROR
Definition: my_base.h:1141
#define DBUG_PRINT(keyword, arglist)
Definition: my_dbug.h:180
uint64_t table_map
Definition: my_table_map.h:29
static char * path
Definition: mysqldump.cc:130
std::string join(Container cont, const std::string &delim)
join elements of an container into a string separated by a delimiter.
Definition: string.h:150
EXPLAIN FORMAT=<format> <command>.
Explain_sort_clause
Enumeration of ORDER BY, GROUP BY and DISTINCT clauses for array indexing.
Definition: opt_explain_format.h:425
@ ESC_none
Definition: opt_explain_format.h:426
@ ESP_EXISTS
Original query has this clause.
Definition: opt_explain_format.h:441
@ ESP_none
Definition: opt_explain_format.h:440
required string key
Definition: replication_asynchronous_connection_failover.proto:59
Classes for query execution.
Common types of the Optimizer, used by optimization and execution.
int plan_idx
This represents the index of a JOIN_TAB/QEP_TAB in an array.
Definition: sql_opt_exec_shared.h:53
@ REF_SLICE_ACTIVE
The slice which is used during evaluation of expressions; Item_ref::ref points there.
Definition: sql_opt_exec_shared.h:612
bool evaluate_during_optimization(const Item *item, const Query_block *select)
Checks if an Item, which is constant for execution, can be evaluated during optimization.
Definition: sql_optimizer.cc:11134
Item * make_cond_for_table(THD *thd, Item *cond, table_map tables, table_map used_table, bool exclude_expensive_cond)
Extract a condition that can be checked after reading given table.
Definition: sql_optimizer.cc:9205
double calculate_subquery_executions(const Item_subselect *subquery, Opt_trace_context *trace)
Estimates how many times a subquery will be executed as part of a query execution.
Definition: sql_optimizer.cc:10937
Key_use_array * create_keyuse_for_table(THD *thd, uint keyparts, Item_field **fields, const mem_root_deque< Item * > &outer_exprs)
Create a keyuse array for a table with a primary key.
Definition: sql_optimizer.cc:8242
ORDER * create_order_from_distinct(THD *thd, Ref_item_array ref_item_array, ORDER *order_list, mem_root_deque< Item * > *fields, bool skip_aggregates, bool convert_bit_fields_to_long, bool *all_order_by_fields_used)
Create an order list that consists of all non-const fields and items.
Definition: sql_optimizer.cc:10401
bool field_time_cmp_date(const Field *f, const Item *v)
Returns true if arguments are a temporal Field having no date, part and a temporal expression having ...
Definition: sql_optimizer.h:1103
bool optimize_cond(THD *thd, Item **conds, COND_EQUAL **cond_equal, mem_root_deque< TABLE_LIST * > *join_list, Item::cond_result *cond_value)
Optimize conditions by.
Definition: sql_optimizer.cc:10035
bool ref_lookup_subsumes_comparison(Field *field, Item *right_item)
Whether a ref lookup of “right_item” on “field” will give an exact comparison in all cases,...
Definition: sql_optimizer.cc:8677
bool is_indexed_agg_distinct(JOIN *join, mem_root_deque< Item_field * > *out_args)
Check for the presence of AGGFN(DISTINCT a) queries that may be subject to loose index scan.
Definition: sql_optimizer.cc:7837
bool remove_eq_conds(THD *thd, Item *cond, Item **retcond, Item::cond_result *cond_value)
Removes const and eq items.
Definition: sql_optimizer.cc:10154
Access paths are a query planning structure that correspond 1:1 to iterators, in that an access path ...
Definition: access_path.h:188
Definition: sql_optimizer.h:169
Temp_table_param * temp_table_param
Definition: sql_optimizer.h:174
TABLE * table
Definition: sql_optimizer.h:170
Definition: lock.h:38
Definition: table.h:279
A position of table within a join order.
Definition: sql_select.h:351
Definition: sql_optimizer.h:82
Item ** arg_value
Definition: sql_optimizer.h:84
Field * field
Definition: sql_optimizer.h:83
uint num_values
Definition: sql_optimizer.h:85
Definition: table.h:2684
Definition: table.h:1394
unsigned int uint
Definition: uca-dump.cc:29
#define PSI_NOT_INSTRUMENTED
Definition: validate_password_imp.cc:39
int n
Definition: xcom_base.cc:505