MDEV-33281 Optimizer hints cleanup: add `const` specifiers, comments

sql/opt_hints.cc

@@ -685,7 +685,7 @@ bool Optimizer_hint_parser::Qb_name_hint::resolve(Parse_context *pc) const
 }
 
 
-bool Optimizer_hint_parser::Hint_list::resolve(Parse_context *pc)
+bool Optimizer_hint_parser::Hint_list::resolve(Parse_context *pc) const
 {
   if (pc->thd->lex->create_view)
   {
@@ -699,20 +699,20 @@ bool Optimizer_hint_parser::Hint_list::resolve(Parse_context *pc)
   if (!get_qb_hints(pc))
     return true;
 
-  List_iterator_fast<Optimizer_hint_parser::Hint> li(*this);
-  while(Optimizer_hint_parser::Hint *hint= li++)
+  for (Hint_list::const_iterator li= this->cbegin(); li != this->cend(); ++li)
   {
-    if (const Table_level_hint &table_hint= *hint)
+    const Optimizer_hint_parser::Hint &hint= *li;
+    if (const Table_level_hint &table_hint= hint)
     {
       if (table_hint.resolve(pc))
         return true;
     }
-    else if (const Index_level_hint &index_hint= *hint)
+    else if (const Index_level_hint &index_hint= hint)
     {
       if (index_hint.resolve(pc))
         return true;
     }
-    else if (const Qb_name_hint &qb_hint= *hint)
+    else if (const Qb_name_hint &qb_hint= hint)
     {
       if (qb_hint.resolve(pc))
         return true;

sql/opt_hints.h

@@ -15,7 +15,50 @@
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */
 
 /*
-  Parse tree node classes for optimizer hint syntax
+  HintsArchitecture
+
+  == Parsing ==
+  Hints have a separate parser, see sql/opt_hint_parser.{h,cc}
+  The parser is invoked separately for each occurence of
+
+    SELECT / *+ hint_body * /  ...
+
+  in the query. The result of parsing is saved in
+  SELECT_LEX::parsed_optimizer_hints.
+
+  == Hint "resolution" ==
+
+  This is done using "resolve" method of parsed data structures
+  This process
+  - Creates interpreted hint structures: Opt_hints_global, Opt_hints_qb,
+    Opt_hints_table, Opt_hints_key.
+  - Interprets QB_NAME hints and assigns Query Block names.
+  - Table-level hints are put into their Query Block's Opt_hints_qb object.
+  - Index-level hints are put into their table's Opt_hints_table object.
+
+  == Hint "adjustment" ==
+
+  During Name Resolution, setup_tables() calls adjust_table_hints() for each
+  table and sets TABLE_LIST::opt_hints_table to point to its Opt_hints_table.
+
+  == Hint hierarchy ==
+
+  Hints have this hierarchy, parent to child:
+
+    Opt_hints_global
+      Opt_hints_qb
+        Opt_hints_table
+          Opt_hints_key
+
+  For some hints, one needs to check the hint's base object and its parent. For
+  example, MRR can be disabled on a per-index or a per-table basis.
+
+  == How the optimizer checks hints  ==
+
+  The optimizer checks what hints specify using these calls:
+    hint_table_state()
+    hint_table_state_or_fallback()
+    hint_key_state()
 */
 
 

sql/opt_hints_parser.h

@@ -218,29 +218,29 @@ public:
 
 private:
 
-  using PARSER= Optimizer_hint_parser; // for a shorter notation
+  using Parser= Optimizer_hint_parser; // for a shorter notation
 
   // Rules consisting of a single token
 
-  class TokenAT: public TOKEN<PARSER, TokenID::tAT>
+  class TokenAT: public TOKEN<Parser, TokenID::tAT>
   {
   public:
     using TOKEN::TOKEN;
   };
 
-  class TokenEOF: public TOKEN<PARSER, TokenID::tEOF>
+  class TokenEOF: public TOKEN<Parser, TokenID::tEOF>
   {
   public:
     using TOKEN::TOKEN;
   };
 
-  class Keyword_QB_NAME: public TOKEN<PARSER, TokenID::keyword_QB_NAME>
+  class Keyword_QB_NAME: public TOKEN<Parser, TokenID::keyword_QB_NAME>
   {
   public:
     using TOKEN::TOKEN;
   };
 
-  class Identifier: public TOKEN<PARSER, TokenID::tIDENT>
+  class Identifier: public TOKEN<Parser, TokenID::tIDENT>
   {
   public:
     using TOKEN::TOKEN;
@@ -258,13 +258,13 @@ private:
     }
   };
 
-  class LParen: public TOKEN<PARSER, TokenID::tLPAREN>
+  class LParen: public TOKEN<Parser, TokenID::tLPAREN>
   {
   public:
     using TOKEN::TOKEN;
   };
 
-  class RParen: public TOKEN<PARSER, TokenID::tRPAREN>
+  class RParen: public TOKEN<Parser, TokenID::tRPAREN>
   {
   public:
     using TOKEN::TOKEN;
@@ -285,7 +285,7 @@ private:
              id == TokenID::keyword_NO_BNL;
     }
   };
-  class Table_level_hint_type: public TokenChoice<PARSER,
+  class Table_level_hint_type: public TokenChoice<Parser,
                                                   Table_level_hint_type_cond>
   {
   public:
@@ -305,7 +305,7 @@ private:
              id == TokenID::keyword_NO_MRR;
     }
   };
-  class Index_level_hint_type: public TokenChoice<PARSER,
+  class Index_level_hint_type: public TokenChoice<Parser,
                                                   Index_level_hint_type_cond>
   {
   public:
@@ -343,7 +343,7 @@ private:
   /*
     at_query_block_name ::= @ query_block_name
   */
-  class At_query_block_name: public AND2<PARSER, TokenAT, Query_block_name>
+  class At_query_block_name: public AND2<Parser, TokenAT, Query_block_name>
   {
   public:
     using AND2::AND2;
@@ -353,7 +353,7 @@ private:
   /*
     opt_qb_name ::=  [ @ query_block_name ]
   */
-  class Opt_qb_name: public OPT<PARSER, At_query_block_name>
+  class Opt_qb_name: public OPT<Parser, At_query_block_name>
   {
   public:
     using OPT::OPT;
@@ -362,7 +362,7 @@ private:
   /*
     hint_param_table ::= table_name opt_qb_name
   */
-  class Hint_param_table: public AND2<PARSER, Table_name, Opt_qb_name>
+  class Hint_param_table: public AND2<Parser, Table_name, Opt_qb_name>
   {
   public:
     using AND2::AND2;
@@ -382,7 +382,7 @@ private:
     size_t count() const { return elements; }
   };
 
-  class Opt_hint_param_table_list: public LIST<PARSER,
+  class Opt_hint_param_table_list: public LIST<Parser,
                                                Hint_param_table_list_container,
                                                Hint_param_table,
                                                TokenID::tCOMMA, 0>
@@ -403,7 +403,7 @@ private:
     size_t count() const { return elements; }
   };
 
-  class Opt_table_name_list: public LIST<PARSER,
+  class Opt_table_name_list: public LIST<Parser,
                                          Table_name_list_container,
                                          Table_name, TokenID::tCOMMA, 0>
   {
@@ -425,7 +425,7 @@ private:
     size_t count() const { return elements; }
   };
 
-  class Opt_hint_param_index_list: public LIST<PARSER,
+  class Opt_hint_param_index_list: public LIST<Parser,
                                                Hint_param_index_list_container,
                                                Hint_param_index,
                                                TokenID::tCOMMA, 0>
@@ -439,7 +439,7 @@ private:
     hint_param_table_ext ::=   hint_param_table
                              | @ query_block_name table_name
   */
-  class At_query_block_name_table_name: public AND2<PARSER,
+  class At_query_block_name_table_name: public AND2<Parser,
                                                     At_query_block_name,
                                                     Table_name>
   {
@@ -465,7 +465,7 @@ private:
     }
   };
 
-  class Hint_param_table_ext: public OR2C<PARSER,
+  class Hint_param_table_ext: public OR2C<Parser,
                                           Hint_param_table_ext_container,
                                           Hint_param_table,
                                           At_query_block_name_table_name>
@@ -480,7 +480,7 @@ private:
       @ query_block_name opt_table_name_list
   */
   class At_query_block_name_opt_table_name_list: public AND2<
-                                                    PARSER,
+                                                    Parser,
                                                     At_query_block_name,
                                                     Opt_table_name_list>
   {
@@ -494,7 +494,7 @@ private:
                            | opt_hint_param_table_list
   */
   class Table_level_hint_body: public OR2<
-                                        PARSER,
+                                        Parser,
                                         At_query_block_name_opt_table_name_list,
                                         Opt_hint_param_table_list>
   {
@@ -503,7 +503,7 @@ private:
   };
 
   // table_level_hint ::= table_level_hint_type ( table_level_hint_body )
-  class Table_level_hint: public AND4<PARSER,
+  class Table_level_hint: public AND4<Parser,
                                       Table_level_hint_type,
                                       LParen,
                                       Table_level_hint_body,
@@ -517,7 +517,7 @@ private:
 
 
   // index_level_hint_body ::= hint_param_table_ext opt_hint_param_index_list
-  class Index_level_hint_body: public AND2<PARSER,
+  class Index_level_hint_body: public AND2<Parser,
                                            Hint_param_table_ext,
                                            Opt_hint_param_index_list>
   {
@@ -527,7 +527,7 @@ private:
 
 
   // index_level_hint ::= index_level_hint_type ( index_level_hint_body )
-  class Index_level_hint: public AND4<PARSER,
+  class Index_level_hint: public AND4<Parser,
                                       Index_level_hint_type,
                                       LParen,
                                       Index_level_hint_body,
@@ -541,7 +541,7 @@ private:
 
 
   // qb_name_hint ::= QB_NAME ( query_block_name )
-  class Qb_name_hint: public AND4<PARSER,
+  class Qb_name_hint: public AND4<Parser,
                                   Keyword_QB_NAME,
                                   LParen,
                                   Query_block_name,
@@ -559,7 +559,7 @@ private:
              | table_level_hint
              | qb_name_hint
   */
-  class Hint: public OR3<PARSER,
+  class Hint: public OR3<Parser,
                          Index_level_hint,
                          Table_level_hint,
                          Qb_name_hint>
@@ -579,13 +579,13 @@ private:
     size_t count() const { return elements; }
   };
 
-  class Hint_list: public LIST<PARSER, Hint_list_container,
+  class Hint_list: public LIST<Parser, Hint_list_container,
                                Hint, TokenID::tNULL/*not separated list*/, 1>
   {
   public:
     using LIST::LIST;
     
-    bool resolve(Parse_context *pc);
+    bool resolve(Parse_context *pc) const;
   };
 
 public:
@@ -593,7 +593,7 @@ public:
     The main rule:
       hints ::= hint_list EOF
   */
-  class Hints: public AND2<PARSER, Hint_list, TokenEOF>
+  class Hints: public AND2<Parser, Hint_list, TokenEOF>
   {
   public:
     using AND2::AND2;

sql/simple_parser.h

@@ -21,6 +21,41 @@
 
 #include "simple_tokenizer.h"
 
+/*
+  A set of templates for constructing a recursive-descent LL(1) parser.
+
+  One is supposed to define classes corresponding to grammar productions.
+  The class should inherit from the grammar rule template. For example, a
+  grammar rule
+
+    foo := bar, baz
+
+  is implemented with
+
+    class Bar ... ; // "bar" is parsed into Bar object
+    class Baz ... ; // "baz" is parsed into Baz object
+
+    // "foo" is parsed into a Foo object.
+    class Foo: public Parser_templates::AND2<PARSER_Impl, Bar, Baz> {
+      using AND2::AND2;
+      ...
+    };
+
+  Parsing code is generated by inheriting AND2's constructors with "using" like
+  shown above. All grammar rule-based classes should also have
+  - a capability to construct an "empty"(i.e. invalid) object with the default
+    constructor. This will be invoked when parsing fails.
+  - operator bool() which returns true if the object is non-empty (i.e. valid)
+    and false otherwise.
+
+  Parsing is done by constructing parser output from the parser object:
+
+    Foo parsed_output(parser);
+
+  PARSER_Impl here is a class implementing a tokenizer and error condition
+  storage, like Extended_string_tokenizer.
+*/
+
 class Parser_templates
 {
 protected:

sql/sql_lex.h

@@ -1273,7 +1273,7 @@ public:
   /* it is for correct printing SELECT options */
   thr_lock_type lock_type;  
 
-  Optimizer_hint_parser_output *parsed_optimizer_hints;
+  const Optimizer_hint_parser_output *parsed_optimizer_hints;
 
   /** System Versioning */
   int vers_setup_conds(THD *thd, TABLE_LIST *tables);