On data tuples being updated or inserted (but not searched for),

set type->len to the prefix_len of the index column, if it is a prefix index.
This should prevent bugs similar to Bug #21638 from occurring.

dict_index_copy_types(): Set type->len to prefix_len if prefix_len != 0.

row_build_index_entry(): Set type->len to prefix_len if prefix_len != 0,
also when the column in the tuple is SQL NULL, because the type information
may be used for interpreting other records during btr_page_reorganize().

dict/dict0dict.c

@@ -1723,8 +1723,6 @@ dict_index_copy_types(
 	dict_index_t*	index,		/* in: index */
 	ulint		n_fields)	/* in: number of field types to copy */
 {
-	dtype_t*	dfield_type;
-	dtype_t*	type;
 	ulint		i;
 
 	if (UNIV_UNLIKELY(index->type & DICT_UNIVERSAL)) {
@@ -1734,10 +1732,17 @@ dict_index_copy_types(
 	}
 
 	for (i = 0; i < n_fields; i++) {
+		dict_field_t*	ifield;
+		dtype_t*	dfield_type;
+		dtype_t*	type;
+
+		ifield = dict_index_get_nth_field(index, i);
 		dfield_type = dfield_get_type(dtuple_get_nth_field(tuple, i));
-		type = dict_col_get_type(dict_field_get_col
-					 (dict_index_get_nth_field(index, i)));
+		type = dict_col_get_type(dict_field_get_col(ifield));
 		*dfield_type = *type;
+		if (UNIV_UNLIKELY(ifield->prefix_len)) {
+			dfield_type->len = ifield->prefix_len;
+		}
 	}
 }
 

row/row0row.c

@@ -143,17 +143,22 @@ row_build_index_entry(
 		dfield_copy(dfield, dfield2);
 
 		/* If a column prefix index, take only the prefix */
-		if (ind_field->prefix_len > 0
-		    && dfield_get_len(dfield2) != UNIV_SQL_NULL) {
+		if (ind_field->prefix_len) {
+			if (dfield_get_len(dfield2) != UNIV_SQL_NULL) {
 
-			cur_type = dict_col_get_type
-				(dict_field_get_col(ind_field));
+				cur_type = dict_col_get_type
+					(dict_field_get_col(ind_field));
+
+				storage_len = dtype_get_at_most_n_mbchars
+					(cur_type,
+					 ind_field->prefix_len,
+					 dfield_get_len(dfield2),
+					 dfield2->data);
 
-			storage_len = dtype_get_at_most_n_mbchars
-				(cur_type, ind_field->prefix_len,
-				 dfield_get_len(dfield2), dfield2->data);
+				dfield_set_len(dfield, storage_len);
+			}
 
-			dfield_set_len(dfield, storage_len);
+			dfield_get_type(dfield)->len = ind_field->prefix_len;
 		}
 	}