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(). 

1 files changed, 22 insertions, 3 deletions

diff --git a/sql/item.cc b/sql/item.cc
index a919dc4c133..b4aa87cd4df 100644
--- a/sql/item.cc
+++ b/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),