MySQL  8.0.20
Source Code Documentation
opt_explain.h
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22 
23 #ifndef OPT_EXPLAIN_INCLUDED
24 #define OPT_EXPLAIN_INCLUDED
25 
26 /**
27  @file sql/opt_explain.h
28  EXPLAIN @<command@>.
29 
30 Single table UPDATE/DELETE commands are explained by the
31 explain_single_table_modification() function.
32 
33 A query expression (complete SELECT query possibly including
34 subqueries and unions), INSERT...SELECT and multitable UPDATE/DELETE
35 commands are explained like this:
36 
37 (1) explain_query_expression()
38 
39 Is the entry point. Forwards the job to explain_unit().
40 
41 (2) explain_unit()
42 
43 Is for a SELECT_LEX_UNIT, prepares, optimizes, explains one JOIN for
44 each "top-level" SELECT_LEXs of the unit (like: all SELECTs of a
45 UNION; but not subqueries), and one JOIN for the fake SELECT_LEX of
46 UNION); each JOIN explain (JOIN::exec()) calls explain_query_specification()
47 
48 (3) explain_query_specification()
49 
50 Is for a single SELECT_LEX (fake or not). It needs a prepared and
51 optimized JOIN, for which it builds the EXPLAIN rows. But it also
52 launches the EXPLAIN process for "inner units" (==subqueries of this
53 SELECT_LEX), by calling explain_unit() for each of them.
54 */
55 
56 #include <string>
57 #include <vector>
58 
59 #include "my_base.h"
60 #include "my_sqlcommand.h"
61 #include "my_thread_local.h"
62 #include "sql/opt_explain_format.h"
64 #include "sql/query_result.h" // Query_result_send
65 #include "sql/row_iterator.h"
66 #include "sql/sql_cmd.h" // Sql_cmd
67 #include "sql/sql_lex.h"
68 #include "sys/types.h"
69 
70 #include <functional>
71 #include <string>
72 
73 class Item;
74 class JOIN;
75 class QEP_TAB;
76 class SELECT_LEX;
77 class SELECT_LEX_UNIT;
78 class THD;
79 struct TABLE;
80 template <class T>
81 class List;
82 
83 extern const char *join_type_str[];
84 
85 /** Table modification plan for JOIN-less statements (update/delete) */
87  public:
88  THD *const thd; ///< Owning thread
89  const enum_mod_type
90  mod_type; ///< Modification type - MT_INSERT/MT_UPDATE/etc
91  TABLE *table; ///< Table to modify
92 
93  QEP_TAB *tab; ///< QUICK access method + WHERE clause
94  uint key; ///< Key to use
95  ha_rows limit; ///< Limit
96  bool need_tmp_table; ///< Whether tmp table needs to be used
97  bool need_sort; ///< Whether to use filesort
98  bool used_key_is_modified; ///< Whether the key used to scan is modified
99  const char *message; ///< Arbitrary message
100  bool zero_result; ///< true <=> plan will not be executed
101  ha_rows examined_rows; ///< # of rows expected to be examined in the table
102 
103  Modification_plan(THD *thd_arg, enum_mod_type mt, QEP_TAB *qep_tab,
104  uint key_arg, ha_rows limit_arg, bool need_tmp_table_arg,
105  bool need_sort_arg, bool used_key_is_modified_arg,
106  ha_rows rows);
107 
108  Modification_plan(THD *thd_arg, enum_mod_type mt, TABLE *table_arg,
109  const char *message_arg, bool zero_result_arg,
110  ha_rows rows);
111 
113 
114  private:
115  void register_in_thd();
116 };
117 
118 /**
119  EXPLAIN functionality for Query_result_insert, Query_result_update and
120  Query_result_delete.
121 
122  This class objects substitute Query_result_insert, Query_result_update and
123  Query_result_delete data interceptor objects to implement EXPLAIN for INSERT,
124  REPLACE and multi-table UPDATE and DELETE queries.
125  Query_result_explain class object initializes tables like Query_result_insert,
126  Query_result_update or Query_result_delete data interceptor do, but it
127  suppresses table data modification by the underlying interceptor object.
128  Thus, we can use Query_result_explain object in the context of EXPLAIN INSERT/
129  REPLACE/UPDATE/DELETE query like we use Query_result_send in the context of
130  EXPLAIN SELECT command:
131  1) in presence of lex->describe flag, pass Query_result_explain object to
132  execution function,
133  2) it calls prepare(), optimize() and start_execution() functions
134  to mark modified tables etc.
135 */
136 
138  protected:
139  /**
140  Pointer to underlying Query_result_insert, Query_result_update or
141  Query_result_delete object.
142  */
144 
145  public:
146  Query_result_explain(SELECT_LEX_UNIT *unit_arg, Query_result *interceptor_arg)
147  : Query_result_send(), interceptor(interceptor_arg) {
148  unit = unit_arg;
149  }
150 
151  protected:
152  bool prepare(THD *thd, List<Item> &list, SELECT_LEX_UNIT *u) override {
153  return Query_result_send::prepare(thd, list, u) ||
154  interceptor->prepare(thd, list, u);
155  }
156 
157  bool start_execution(THD *thd) override {
159  interceptor->start_execution(thd);
160  }
161 
162  bool optimize() override {
163  return Query_result_send::optimize() || interceptor->optimize();
164  }
165 
166  void cleanup(THD *thd) override {
168  interceptor->cleanup(thd);
169  }
170 };
171 
172 bool explain_no_table(THD *explain_thd, const THD *query_thd,
173  SELECT_LEX *select_lex, const char *message,
175 bool explain_single_table_modification(THD *explain_thd, const THD *query_thd,
176  const Modification_plan *plan,
177  SELECT_LEX *select);
178 bool explain_query(THD *explain_thd, const THD *query_thd,
179  SELECT_LEX_UNIT *unit);
180 bool explain_query_specification(THD *explain_thd, const THD *query_thd,
181  SELECT_LEX *select_lex,
183 
185  public:
187  : m_thread_id(thread_id) {}
188 
190  return SQLCOM_EXPLAIN_OTHER;
191  }
192 
193  bool execute(THD *thd) override;
194 
195  private:
196  /// connection_id in EXPLAIN FOR CONNECTION <connection_id>
198 };
199 
200 // Print out an iterator and all of its children (if any) in a tree.
201 // "level" is the current indenting level, as this is called recursively.
202 std::string PrintQueryPlan(int level, RowIterator *iterator);
203 
204 // For each subselect within the given item, call the given functor
205 // with its SELECT number, dependent/cacheable status and an iterator.
206 void ForEachSubselect(
207  Item *parent_item,
208  const std::function<void(int select_number, bool is_dependent,
209  bool is_cacheable, RowIterator *iterator)>
210  &callback);
211 
212 // For the given join, return a list of pseudo-children corresponding to
213 // subselects in the SELECT list (if any).
214 std::vector<RowIterator::Child> GetIteratorsFromSelectList(JOIN *join);
215 
216 #endif /* OPT_EXPLAIN_INCLUDED */
ha_rows limit
Limit.
Definition: opt_explain.h:95
Representation of an SQL command.
Definition: sql_cmd.h:63
Definition: sql_optimizer.h:175
bool explain_query_specification(THD *explain_thd, const THD *query_thd, SELECT_LEX *select_lex, enum_parsing_context ctx)
Explain select_lex&#39;s join.
Definition: opt_explain.cc:1912
TABLE * table
Table to modify.
Definition: opt_explain.h:91
QEP_TAB * tab
QUICK access method + WHERE clause.
Definition: opt_explain.h:93
bool prepare(THD *thd, List< Item > &list, SELECT_LEX_UNIT *u) override
Perform preparation specific to the query expression or DML statement.
Definition: opt_explain.h:152
enum_mod_type
Definition: opt_explain_format.h:132
enum_sql_command sql_command_code() const override
Return the command code for this statement.
Definition: opt_explain.h:189
ha_rows examined_rows
of rows expected to be examined in the table
Definition: opt_explain.h:101
virtual bool prepare(THD *, List< Item > &, SELECT_LEX_UNIT *u)
Perform preparation specific to the query expression or DML statement.
Definition: query_result.h:89
bool explain_single_table_modification(THD *explain_thd, const THD *query_thd, const Modification_plan *plan, SELECT_LEX *select)
EXPLAIN handling for single-table UPDATE and DELETE queries.
Definition: opt_explain.cc:1821
const char * message
Arbitrary message.
Definition: opt_explain.h:99
my_thread_id m_thread_id
connection_id in EXPLAIN FOR CONNECTION <connection_id>
Definition: opt_explain.h:197
enum_parsing_context
Names for different query parse tree parts.
Definition: parse_tree_node_base.h:55
A context for reading through a single table using a chosen access method: index read, scan, etc, use of cache, etc.
Definition: row_iterator.h:61
void cleanup(THD *) override
Cleanup after this execution.
Definition: query_result.h:203
std::string PrintQueryPlan(int level, RowIterator *iterator)
Definition: opt_explain.cc:2018
This class represents a query block, aka a query specification, which is a query consisting of a SELE...
Definition: sql_lex.h:997
Query_result_explain(SELECT_LEX_UNIT *unit_arg, Query_result *interceptor_arg)
Definition: opt_explain.h:146
enum_sql_command
Definition: my_sqlcommand.h:45
~Modification_plan()
Definition: opt_explain.cc:2583
bool explain_no_table(THD *explain_thd, const THD *query_thd, SELECT_LEX *select_lex, const char *message, enum_parsing_context ctx)
Send a message as an "extra" column value.
Definition: opt_explain.cc:1766
Definition: query_result.h:48
std::string join(Container cont, const std::string &delim)
join elements of an container into a string seperated by a delimiter.
Definition: string.h:144
void register_in_thd()
Definition: opt_explain.cc:2493
class udf_list * list
static bool execute(MYSQL_STMT *stmt, char *packet, ulong length)
Definition: libmysql.cc:1918
Representation of an SQL command.
bool need_tmp_table
Whether tmp table needs to be used.
Definition: opt_explain.h:96
bool start_execution(THD *thd) override
Prepare for execution of the query expression or DML statement.
Definition: opt_explain.h:157
const char * join_type_str[]
Definition: opt_explain.cc:111
Definition: table.h:1306
EXPLAIN functionality for Query_result_insert, Query_result_update and Query_result_delete.
Definition: opt_explain.h:137
This file includes constants used by all storage engines.
EXPLAIN FORMAT=<format> <command>.
bool need_sort
Whether to use filesort.
Definition: opt_explain.h:97
bool optimize() override
Optimize the result processing of a query expression, applicable to data change operation (not simple...
Definition: opt_explain.h:162
Sql_cmd_explain_other_thread(my_thread_id thread_id)
Definition: opt_explain.h:186
Definition: aggregate_check.h:523
void cleanup(THD *thd) override
Cleanup after this execution.
Definition: opt_explain.h:166
Definition: my_sqlcommand.h:181
Definition: item.h:740
unsigned int uint
Definition: uca-dump.cc:29
#define final(a, b, c)
Definition: hash.c:109
This class represents a query expression (one query block or several query blocks combined with UNION...
Definition: sql_lex.h:587
uint key
Key to use.
Definition: opt_explain.h:94
bool explain_query(THD *explain_thd, const THD *query_thd, SELECT_LEX_UNIT *unit)
EXPLAIN handling for SELECT, INSERT/REPLACE SELECT, and multi-table UPDATE/DELETE queries...
Definition: opt_explain.cc:2204
Definition: sql_executor.h:270
std::vector< RowIterator::Child > GetIteratorsFromSelectList(JOIN *join)
Definition: opt_explain.cc:2640
THD *const thd
Owning thread.
Definition: opt_explain.h:88
Definition: query_result.h:187
virtual bool optimize()
Optimize the result processing of a query expression, applicable to data change operation (not simple...
Definition: query_result.h:100
uint32 my_thread_id
Definition: my_thread_local.h:33
Definition: opt_explain.h:184
Table modification plan for JOIN-less statements (update/delete)
Definition: opt_explain.h:86
Modification_plan(THD *thd_arg, enum_mod_type mt, QEP_TAB *qep_tab, uint key_arg, ha_rows limit_arg, bool need_tmp_table_arg, bool need_sort_arg, bool used_key_is_modified_arg, ha_rows rows)
Modification_plan&#39;s constructor, to represent that we will use an access method on the table...
Definition: opt_explain.cc:2524
virtual bool start_execution(THD *)
Prepare for execution of the query expression or DML statement.
Definition: query_result.h:111
Query_result * interceptor
Pointer to underlying Query_result_insert, Query_result_update or Query_result_delete object...
Definition: opt_explain.h:143
bool used_key_is_modified
Whether the key used to scan is modified.
Definition: opt_explain.h:98
virtual void cleanup(THD *)
Cleanup after this execution.
Definition: query_result.h:151
void ForEachSubselect(Item *parent_item, const std::function< void(int select_number, bool is_dependent, bool is_cacheable, RowIterator *iterator)> &callback)
const enum_mod_type mod_type
Modification type - MT_INSERT/MT_UPDATE/etc.
Definition: opt_explain.h:90
my_off_t ha_rows
Definition: my_base.h:1132
static my_thread_id thread_id
Definition: my_thr_init.cc:62
For each client connection we create a separate thread with THD serving as a thread/connection descri...
Definition: sql_class.h:765
bool zero_result
true <=> plan will not be executed
Definition: opt_explain.h:100