1 files changed, 12 insertions, 0 deletions
diff --git a/sql/field.h b/sql/field.h
index 75bb96f2f6d..e6188d43f57 100644
--- a/sql/field.h
+++ b/sql/field.h
@@ -98,6 +98,18 @@ public:
   virtual void store_time(TIME *ltime,timestamp_type t_type);
   virtual double val_real(void)=0;
   virtual longlong val_int(void)=0;
+  String *val_str(String *str) { return val_str(str, str); }
+  /* val_str(buf1, buf2) gets two buffers and should use them as follows:
+     if it needs a temp buffer to convert result to string - use buf1
+       example Field_tiny::val_str()
+     if the value exists as a string already - use buf2
+       example Field_string::val_str()
+     consequently, buf2 may be created as 'String buf;' - no memory
+     will be allocated for it. buf1 will be allocated to hold a
+     value if it's too small. Using allocated buffer for buf2 may result in
+     an unnecessary free (and later, may be an alloc).
+     This trickery is used to decrease a number of malloc calls.
+  */
   virtual String *val_str(String*,String *)=0;
   virtual Item_result result_type () const=0;
   virtual Item_result cmp_type () const { return result_type(); }