"Fix" for BUG #2050 "10 to 1 performance drop with server 4.1.1".

Actually it is not a bug but right behavior observed as pefomance 
degradation after we have forced Item_field::fix_fields() to 
re-execute each time when we are executing prep stmt.

This patch implements small optimization which heals this bad 
behavior. We are caching field position in TABLE::field array in
Item's member and are using this position for speeding up field
lookups in fix_fields() in case of its re-execution.


sql/item.cc:
  Added cached_field_index member to Item_ident for caching field
  position in TABLE::field array for quicker field lookup in case 
  fix_fields() is executed twice.
sql/item.h:
  Added cached_field_index member to Item_ident for caching field
  position in TABLE::field array for quicker field lookup in case 
  fix_fields() is executed twice.
sql/mysql_priv.h:
  Now find_field_in_table has one more in-out parameter which is used
  for caching field index in TABLE::field array stored for quicker
  field look up.
sql/sql_acl.cc:
  Now find_field_in_table has one more in-out parameter which is used
  for caching field index in TABLE::field array stored for quicker
  field look up.
sql/sql_base.cc:
  Optimization: Now when we are looking up Field by its name we are 
  caching its position in TABLE::field array in Item_ident::cached_field_index,
  so when we will call fix_fields() second time for this item (e.g.
  when we are re-executing prep statement) we can reuse this index
  to speed up this lookup.
sql/table.cc:
  Now we storing in TABLE::name_hash pointers to elements of 
  TABLE::field array, because this allows easily retrieve index
  of field in this array when it is looked up by its name.
sql/table.h:
  Added comment claryfying what we store in TABLE::name_hash.
BitKeeper/etc/logging_ok:
  Logging to logging@openlogging.org accepted

1 files changed, 2 insertions, 1 deletions

diff --git a/sql/table.h b/sql/table.h
index c027e2ccc44..039e3ded9f3 100644
--- a/sql/table.h
+++ b/sql/table.h
@@ -65,7 +65,8 @@ struct st_table {
   handler *file;
   Field **field;			/* Pointer to fields */
   Field_blob **blob_field;		/* Pointer to blob fields */
-  HASH	name_hash;			/* hash of field names */
+  /* hash of field names (contains pointers to elements of field array) */
+  HASH	name_hash;
   byte *record[2];			/* Pointer to records */
   byte *default_values;          	/* Default values for INSERT */
   byte *insert_values;                  /* used by INSERT ... UPDATE */