Fix for Bug #3307 "FLUSH TABLES sometimes breaks prepared statement

table resolution".
Added members to Item_ident for storing original db, table and field
names since those that set later from Field have shorter life-time 
than required by prep. stmt. So we need to restore original names in 
Item_ident::cleanup(). Also now using special construnctor for creation
of Item_field from Field object that ensures that table and field name 
have big enough life-time.

"Fix" for bug #2050 "10 to 1 performance drop with server 4.1.1"
Clean ups in implementation of caching of field number in table.
Added caching of table in which field is found in find_field_in_tables(). 


sql/item.cc:
  Added members to Item_ident for storing original db, table and field
  names since those that set later from Field have shorter life-time 
  than required by prep. stmt. So we need to restore original names in 
  Item_ident::cleanup().
  Added Item_ident::cached_table for caching table there we found 
  our field.
  Added special constructor for creation of Item_field from Field object
  that ensures that table and field name have big enough life-time.
sql/item.h:
  Added members to Item_ident for storing original db, table and field
  names since those that set later from Field have shorter life-time 
  than required by prep. stmt. So we need to restore original names in 
  Item_ident::cleanup().
  Changed type of Item_ident::cached_field_index from int to uint
  (and so NO_CACHED_FIELD_INDEX is UINT_MAX now) because we want to
  save one comparison in find_field_in_table().
  Added Item_ident::cached_table for caching table there we found 
  our field.
  Added special constructor for creation of Item_field from Field object
  that ensures that table and field name have big enough life-time.
sql/mysql_priv.h:
  Changed type of cached_field_index_ptr from int* to uint*
  (and so NO_CACHED_FIELD_INDEX is UINT_MAX now) because we want to
  save one comparison in find_field_in_table().
sql/sql_acl.cc:
  Changed type of find_field_in_table() paremeter to make it 
  faster.
sql/sql_base.cc:
  find_field_in_table(): small optimization and soime clean ups in 
   caching of field index.
  find_field_in_tables(): added aggresive caching of table in which
   field is found in Item_ident::cached_table.
  insert_fields():
   using special construnctor for creation of Item_field from Field 
   object that ensures that table and field name have big enough life-time.

sql/item.cc

@@ -103,9 +103,12 @@ void Item::print_item_w_name(String *str)
 
 Item_ident::Item_ident(const char *db_name_par,const char *table_name_par,
 		       const char *field_name_par)
-  :changed_during_fix_field(0), db_name(db_name_par),
-   table_name(table_name_par), field_name(field_name_par),
-   cached_field_index(-1), depended_from(0)
+  :
+   orig_db_name(db_name_par), orig_table_name(table_name_par), 
+   orig_field_name(field_name_par), changed_during_fix_field(0), 
+   db_name(db_name_par), table_name(table_name_par), 
+   field_name(field_name_par), cached_field_index(NO_CACHED_FIELD_INDEX), 
+   cached_table(0), depended_from(0)
 {
   name = (char*) field_name_par;
 }
@@ -113,11 +116,15 @@ Item_ident::Item_ident(const char *db_name_par,const char *table_name_par,
 // Constructor used by Item_field & Item_ref (see Item comment)
 Item_ident::Item_ident(THD *thd, Item_ident *item)
   :Item(thd, item),
+   orig_db_name(item->orig_db_name),
+   orig_table_name(item->orig_table_name), 
+   orig_field_name(item->orig_field_name),
    changed_during_fix_field(0),
    db_name(item->db_name),
    table_name(item->table_name),
    field_name(item->field_name),
    cached_field_index(item->cached_field_index),
+   cached_table(item->cached_table),
    depended_from(item->depended_from)
 {}
 
@@ -129,6 +136,9 @@ void Item_ident::cleanup()
     *changed_during_fix_field= this;
     changed_during_fix_field= 0;
   }
+  db_name= orig_db_name; 
+  table_name= orig_table_name;
+  field_name= orig_field_name;
 }
 
 bool Item_ident::remove_dependence_processor(byte * arg)
@@ -310,6 +320,15 @@ Item_field::Item_field(Field *f)
   fixed= 1;
 }
 
+Item_field::Item_field(THD *thd, Field *f)
+  :Item_ident(NullS, thd->strdup(f->table_name), 
+              thd->strdup(f->field_name))
+{
+  set_field(f);
+  collation.set(DERIVATION_IMPLICIT);
+  fixed= 1;
+}
+
 // Constructor need to process subselect with temporary tables (see Item)
 Item_field::Item_field(THD *thd, Item_field *item)
   :Item_ident(thd, item),

sql/item.h

@@ -253,10 +253,20 @@ public:
   virtual Item_num* neg()= 0;
 };
 
+#define NO_CACHED_FIELD_INDEX ((uint)(-1))
 
 class st_select_lex;
 class Item_ident :public Item
 {
+  /* 
+    We have to store initial values of db_name, table_name and field_name
+    to be able to restore them during cleanup() because they can be 
+    updated during fix_fields() to values from Field object and life-time 
+    of those is shorter than life-time of Item_field.
+  */
+  const char *orig_db_name;
+  const char *orig_table_name;
+  const char *orig_field_name;
   Item **changed_during_fix_field;
 public:
   const char *db_name;
@@ -264,9 +274,16 @@ public:
   const char *field_name;
   /* 
     Cached value of index for this field in table->field array, used by prep. 
-    stmts for speeding up their re-execution, -1 if index value is not known.
+    stmts for speeding up their re-execution. Holds NO_CACHED_FIELD_INDEX 
+    if index value is not known.
+  */
+  uint cached_field_index;
+  /*
+    Cached pointer to table which contains this field, used for the same reason
+    by prep. stmt. too in case then we have not-fully qualified field.
+    0 - means no cached value.
   */
-  int cached_field_index;
+  TABLE_LIST *cached_table;
   st_select_lex *depended_from;
   Item_ident(const char *db_name_par,const char *table_name_par,
 	     const char *field_name_par);
@@ -298,6 +315,11 @@ public:
   { collation.set(DERIVATION_IMPLICIT); }
   // Constructor need to process subselect with temporary tables (see Item)
   Item_field(THD *thd, Item_field *item);
+  /*
+    Constructor used inside setup_wild(), ensures that field and table
+    names will live as long as Item_field (important in prep. stmt.)
+  */
+  Item_field(THD *thd, Field *field);
   Item_field(Field *field);
   enum Type type() const { return FIELD_ITEM; }
   bool eq(const Item *item, bool binary_cmp) const;

sql/mysql_priv.h

@@ -559,7 +559,7 @@ Field *find_field_in_tables(THD *thd, Item_ident *item, TABLE_LIST *tables,
 			    TABLE_LIST **where, bool report_error);
 Field *find_field_in_table(THD *thd,TABLE *table,const char *name,uint length,
                            bool check_grant,bool allow_rowid,
-                           int *cached_field_index_ptr);
+                           uint *cached_field_index_ptr);
 #ifdef HAVE_OPENSSL
 #include <openssl/des.h>
 struct st_des_keyblock

sql/sql_acl.cc

@@ -2194,7 +2194,7 @@ int mysql_table_grant(THD *thd, TABLE_LIST *table_list,
       DBUG_RETURN(-1);
     while ((column = column_iter++))
     {
-      int unused_field_idx= -1;
+      uint unused_field_idx= NO_CACHED_FIELD_INDEX;
       if (!find_field_in_table(thd,table,column->column.ptr(),
                                column->column.length(),0,0,
                                &unused_field_idx))

sql/sql_base.cc

@@ -1791,12 +1791,13 @@ bool rm_temporary_table(enum db_type base, char *path)
 
 Field *find_field_in_table(THD *thd,TABLE *table,const char *name,uint length,
                            bool check_grants, bool allow_rowid, 
-                           int *cached_field_index_ptr)
+                           uint *cached_field_index_ptr)
 {
-  Field **field_ptr= 0, *field;
-  int cached_field_index= *cached_field_index_ptr;
+  Field **field_ptr, *field;
+  uint cached_field_index= *cached_field_index_ptr;
 
-  if (cached_field_index >= 0 && cached_field_index < table->fields &&
+  /* We assume here that table->field < NO_CACHED_FIELD_INDEX = UINT_MAX */
+  if (cached_field_index < table->fields &&
       !my_strcasecmp(system_charset_info, 
                      table->field[cached_field_index]->field_name, name))
       field_ptr= table->field + cached_field_index;
@@ -1805,14 +1806,11 @@ Field *find_field_in_table(THD *thd,TABLE *table,const char *name,uint length,
                                     length);
   else
   {
-    if (!(field_ptr=table->field))
+    if (!(field_ptr= table->field))
       return (Field *)0;
-    while (*field_ptr)
-    {
+    for (; *field_ptr; ++field_ptr)
       if (!my_strcasecmp(system_charset_info, (*field_ptr)->field_name, name))
         break;
-      ++field_ptr;
-    }
   }
 
   if (field_ptr && *field_ptr)
@@ -1882,6 +1880,31 @@ find_field_in_tables(THD *thd, Item_ident *item, TABLE_LIST *tables,
   uint length=(uint) strlen(name);
   char name_buff[NAME_LEN+1];
 
+
+  if (item->cached_table)
+  {
+    /*
+      This shortcut is used by prepared statements. We assuming that 
+      TABLE_LIST *tables is not changed during query execution (which 
+      is true for all queries except RENAME but luckily RENAME doesn't 
+      use fields...) so we can rely on reusing pointer to its member.
+      With this optimisation we also miss case when addition of one more
+      field makes some prepared query ambiguous and so erronous, but we 
+      accept this trade off.
+    */
+    found= find_field_in_table(thd,tables->table,name,length,
+                               test(tables->table->grant.want_privilege),
+                               1, &(item->cached_field_index));
+
+    if (found)
+    {
+      (*where)= tables;
+      if (found == WRONG_GRANT)
+        return (Field*) 0;
+      return found;
+    }
+  }
+
   if (db && lower_case_table_names)
   {
     /*
@@ -1909,7 +1932,7 @@ find_field_in_tables(THD *thd, Item_ident *item, TABLE_LIST *tables,
 					1, &(item->cached_field_index));
 	if (find)
 	{
-	  (*where)= tables;
+	  (*where)= item->cached_table= tables;
 	  if (find == WRONG_GRANT)
 	    return (Field*) 0;
 	  if (db || !thd->where)
@@ -1968,7 +1991,7 @@ find_field_in_tables(THD *thd, Item_ident *item, TABLE_LIST *tables,
     {
       if (field == WRONG_GRANT)
 	return (Field*) 0;
-      (*where)= tables;
+      (*where)= item->cached_table= tables;
       if (found)
       {
 	if (!thd->where)			// Returns first found
@@ -2304,7 +2327,7 @@ insert_fields(THD *thd,TABLE_LIST *tables, const char *db_name,
       thd->used_tables|=table->map;
       while ((field = *ptr++))
       {
-	Item_field *item= new Item_field(field);
+	Item_field *item= new Item_field(thd, field);
 	if (!found++)
 	  (void) it->replace(item);		// Replace '*'
 	else