From d2906f0ed07bc06161d749d03ffa8acb7c09c785 Mon Sep 17 00:00:00 2001
From: unknown <dlenev@brandersnatch.localdomain>
Date: Wed, 31 Mar 2004 21:25:55 +0400
Subject: 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.h | 26 ++++++++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

(limited to 'sql/item.h')

diff --git a/sql/item.h b/sql/item.h
index fccdd7f0732..faee51af97e 100644
--- a/sql/item.h
+++ b/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;
-- 
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