MDEV-33281 Optimizer hints cleanup:

- add a comment that opt_hints_global->check_unresolved() is never called
- improve comments
- rename everything with "resolved_children" to "fully_resolved_children"
- Opt_hints_table::adjust_key_hints() now returns value
- less "reach-back-to-parent" logic
- rename Hint "adjustment" and "resolution" (yes, both terms were used)
     to "fixing". "Resolution" is already used for parse-tree objects

sql/opt_hints.cc

@@ -21,8 +21,7 @@
 #include "opt_hints.h"
 
 /**
-  Information about hints. Sould be
-  synchronized with opt_hints_enum enum.
+  Information about hints. Must be in sync with opt_hints_enum.
 
   Note: Hint name depends on hint state. 'NO_' prefix is added
   if appropriate hint state bit(see Opt_hints_map::hints) is not
@@ -176,7 +175,12 @@ static Opt_hints_qb *get_qb_hints(Parse_context *pc)
   {
     global_hints->register_child(qb);
     pc->select->opt_hints_qb= qb;
-    qb->set_resolved();
+    /*
+      Mark the query block as resolved as we know which SELECT_LEX it is
+      attached to.
+      Note that children (indexes, tables) are probably not resolved, yet.
+    */
+    qb->set_fixed();
   }
   return qb;
 }
@@ -272,7 +276,7 @@ void Opt_hints::print(THD *thd, String *str)
 {
   for (uint i= 0; i < MAX_HINT_ENUM; i++)
   {
-    if (is_specified(static_cast<opt_hints_enum>(i)) && is_resolved())
+    if (is_specified(static_cast<opt_hints_enum>(i)) && is_fixed())
     {
       append_hint_type(str, static_cast<opt_hints_enum>(i));
       str->append(STRING_WITH_LEN("("));
@@ -308,7 +312,7 @@ void Opt_hints::append_hint_type(String *str, opt_hints_enum type)
 }
 
 
-void Opt_hints::print_warn_unresolved(THD *thd)
+void Opt_hints::print_unfixed_warnings(THD *thd)
 {
   String hint_name_str, hint_type_str;
   append_name(thd, &hint_name_str);
@@ -320,24 +324,29 @@ void Opt_hints::print_warn_unresolved(THD *thd)
       hint_type_str.length(0);
       append_hint_type(&hint_type_str, static_cast<opt_hints_enum>(i));
       push_warning_printf(thd, Sql_condition::WARN_LEVEL_WARN,
-                          get_warn_unresolved_code(),
-                          ER_THD(thd, get_warn_unresolved_code()),
+                          get_unfixed_warning_code(),
+                          ER_THD(thd, get_unfixed_warning_code()),
                           hint_name_str.c_ptr_safe(),
                           hint_type_str.c_ptr_safe());
     }
   }
 }
 
+/*
+  @brief
+    Recursively walk the descendant hints and emit warnings for any
+    unresolved hints
+*/
 
-void Opt_hints::check_unresolved(THD *thd)
+void Opt_hints::check_unfixed(THD *thd)
 {
-  if (!is_resolved())
-    print_warn_unresolved(thd);
+  if (!is_fixed())
+    print_unfixed_warnings(thd);
 
-  if (!is_all_resolved())
+  if (!are_children_fully_fixed())
   {
     for (uint i= 0; i < child_array.size(); i++)
-      child_array[i]->check_unresolved(thd);
+      child_array[i]->check_unfixed(thd);
   }
 }
 
@@ -354,8 +363,8 @@ Opt_hints_qb::Opt_hints_qb(Opt_hints *opt_hints_arg,
 }
 
 
-Opt_hints_table *Opt_hints_qb::adjust_hints_for_table(TABLE *table,
-                                                  const Lex_ident_table &alias)
+Opt_hints_table *Opt_hints_qb::fix_hints_for_table(TABLE *table,
+                                                   const Lex_ident_table &alias)
 {
   Opt_hints_table *tab= static_cast<Opt_hints_table *>(find_by_name(alias));
 
@@ -364,7 +373,9 @@ Opt_hints_table *Opt_hints_qb::adjust_hints_for_table(TABLE *table,
   if (!tab)                            // Tables not found
     return NULL;
 
-  tab->adjust_key_hints(table);
+  if (!tab->fix_hint(table))
+    incr_fully_fixed_children();
+
   return tab;
 }
 
@@ -411,16 +422,18 @@ uint Opt_hints_qb::sj_enabled_strategies(uint opt_switches) const
 /*
   @brief
     For each index IDX, put its hints into keyinfo_array[IDX]
-
 */
-void Opt_hints_table::adjust_key_hints(TABLE *table)
+
+bool Opt_hints_table::fix_hint(TABLE *table)
 {
-  set_resolved();
+  /*
+    Ok, there's a table we attach to. Mark this hint as fixed and proceed to
+    fixing the child objects.
+  */
+  set_fixed();
+
   if (child_array_ptr()->size() == 0)  // No key level hints
-  {
-    get_parent()->incr_resolved_children();
-    return;
-  }
+    return false; // Ok, fully fixed
 
   /* Make sure that adjustment is called only once. */
   DBUG_ASSERT(keyinfo_array.size() == 0);
@@ -434,20 +447,18 @@ void Opt_hints_table::adjust_key_hints(TABLE *table)
     {
       if (key_info->name.streq((*hint)->get_name()))
       {
-        (*hint)->set_resolved();
+        (*hint)->set_fixed();
         keyinfo_array[j]= static_cast<Opt_hints_key *>(*hint);
-        incr_resolved_children();
+        incr_fully_fixed_children();
+        break;
       }
     }
   }
 
-  /*
-   Do not increase number of resolved tables
-   if there are unresolved key objects. It's
-   important for check_unresolved() function.
-  */
-  if (is_all_resolved())
-    get_parent()->incr_resolved_children();
+  if (are_children_fully_fixed())
+    return false;
+
+  return true; // Some children are not fully fixed
 }
 
 
@@ -1105,7 +1116,12 @@ ulonglong Parser::Max_execution_time_hint::get_milliseconds() const
 }
 
 
-bool Opt_hints_global::resolve(THD *thd)
+/*
+  @brief
+    Fix global-level hints (and only them)
+*/
+
+bool Opt_hints_global::fix_hint(THD *thd)
 {
   if (thd->lex->is_ps_or_view_context_analysis())
     return false;
@@ -1113,7 +1129,7 @@ bool Opt_hints_global::resolve(THD *thd)
   if (!max_exec_time_hint)
   {
     /* No possible errors */
-    set_resolved();
+    set_fixed();
     return false;
   }
 
@@ -1136,7 +1152,7 @@ bool Opt_hints_global::resolve(THD *thd)
     thd->reset_query_timer();
     thd->set_query_timer_force(max_exec_time_hint->get_milliseconds() * 1000);
   }
-  set_resolved();
+  set_fixed();
   return false;
 }