MDEV-22241 Refactoring and preparation for the fix

Author: mariadb-OlegSmirnov

sql/sql_lex.h

@@ -3596,14 +3596,31 @@ struct LEX: public Query_tables_list
   static const ulong initial_gtid_domain_buffer_size= 16;
   uint32 gtid_domain_static_buffer[initial_gtid_domain_buffer_size];
 
-  inline void set_limit_rows_examined()
+  /*
+    Activates enforcement of the LIMIT ROWS EXAMINED clause, if present
+    in the query.
+  */
+  void activate_limit_rows_examined()
   {
     if (limit_rows_examined)
       limit_rows_examined_cnt= limit_rows_examined->val_uint();
     else
-      limit_rows_examined_cnt= ULONGLONG_MAX;
+      limit_rows_examined_cnt= ULONGLONG_MAX; // Unreachable value
   }
 
+  /**
+    Deactivates enforcement of the LIMIT ROWS EXAMINED clause and returns its
+    prior state.
+    Return value:
+    - false: LIMIT ROWS EXAMINED was not activated
+    - true:  LIMIT ROWS EXAMINED was activated
+  */
+  bool deactivate_limit_rows_examined()
+  {
+    bool was_activated= (limit_rows_examined_cnt == ULONGLONG_MAX);
+    limit_rows_examined_cnt= ULONGLONG_MAX; // Unreachable value
+    return was_activated;
+  }
 
   LEX_CSTRING *win_ref;
   Window_frame *win_frame;

sql/sql_select.cc

@@ -632,8 +632,8 @@ bool handle_select(THD *thd, LEX *lex, select_result *result,
     thd->abort_on_warning= saved_abort_on_warning;
     thd->reset_killed();
   }
-  /* Disable LIMIT ROWS EXAMINED after query execution. */
-  thd->lex->limit_rows_examined_cnt= ULONGLONG_MAX;
+  /* Deactivate LIMIT ROWS EXAMINED after query execution. */
+  thd->lex->deactivate_limit_rows_examined();
 
   MYSQL_SELECT_DONE((int) res, (ulong) thd->limit_found_rows);
   DBUG_RETURN(res);
@@ -4787,7 +4787,7 @@ void JOIN::exec_inner()
   THD_STAGE_INFO(thd, stage_executing);
 
   /*
-    Enable LIMIT ROWS EXAMINED during query execution if:
+    Activate enforcement of LIMIT ROWS EXAMINED during query execution if:
     (1) This JOIN is the outermost query (not a subquery or derived table)
         This ensures that the limit is enabled when actual execution begins,
         and not if a subquery is evaluated during optimization of the outer
@@ -4799,7 +4799,7 @@ void JOIN::exec_inner()
 
   if (!select_lex->outer_select() &&                            // (1)
       select_lex != select_lex->master_unit()->fake_select_lex) // (2)
-    thd->lex->set_limit_rows_examined();
+    thd->lex->activate_limit_rows_examined();
 
   if (procedure)
   {
@@ -26733,10 +26733,10 @@ JOIN_TAB::remove_duplicates()
     sort_field_keylength+= ptr->length + (ptr->item->maybe_null() ? 1 : 0);
 
   /*
-    Disable LIMIT ROWS EXAMINED in order to avoid interrupting prematurely
+    Deactivate LIMIT ROWS EXAMINED in order to avoid interrupting prematurely
     duplicate removal, and produce a possibly incomplete query result.
   */
-  thd->lex->limit_rows_examined_cnt= ULONGLONG_MAX;
+  thd->lex->deactivate_limit_rows_examined();
   if (thd->killed == ABORT_QUERY)
     thd->reset_killed();
 
@@ -26755,7 +26755,7 @@ JOIN_TAB::remove_duplicates()
                                   sort_field_keylength, having);
 
   if (join->select_lex != join->select_lex->master_unit()->fake_select_lex)
-    thd->lex->set_limit_rows_examined();
+    thd->lex->activate_limit_rows_examined();
   free_blobs(first_field);
   my_free(sortorder);
   DBUG_RETURN(error);

sql/sql_union.cc

@@ -2344,10 +2344,10 @@ bool st_select_lex_unit::exec()
     List<Item_func_match> empty_list;
     empty_list.empty();
     /*
-      Disable LIMIT ROWS EXAMINED in order to produce the possibly incomplete
+      Deactivate LIMIT ROWS EXAMINED in order to produce the possibly incomplete
       result of the UNION without interruption due to exceeding the limit.
     */
-    thd->lex->limit_rows_examined_cnt= ULONGLONG_MAX;
+    thd->lex->deactivate_limit_rows_examined();
 
     // Check if EOM
     if (fake_select_lex != NULL && likely(!thd->is_fatal_error))
@@ -2447,7 +2447,7 @@ bool st_select_lex_unit::exec()
   }
   thd->lex->current_select= lex_select_save;
 err:
-  thd->lex->set_limit_rows_examined();
+  thd->lex->activate_limit_rows_examined();
   if (likely(!saved_error))
     thd->inc_examined_row_count(examined_rows);
   DBUG_RETURN(saved_error);
@@ -2588,7 +2588,7 @@ bool st_select_lex_unit::exec_recursive()
 
   thd->lex->current_select= lex_select_save;
 err:
-  thd->lex->set_limit_rows_examined();
+  thd->lex->activate_limit_rows_examined();
   DBUG_RETURN(saved_error);    
 }