Fix update of the metadata record

btr_cur_pessimistic_update(): Invoke dtuple_convert_big_rec()
for metadata records if the record is too large, or if the
metadata field is not yet marked as externally stored.

row_upd_index_replace_metadata(): Correctly copy the ALTER TABLE
metadata field.

storage/innobase/btr/btr0cur.cc

@@ -4799,8 +4799,9 @@ btr_cur_pessimistic_update(
 		    dict_index_get_n_fields(index),
 		    block->page.size)
 	    || (UNIV_UNLIKELY(update->is_alter_metadata())
-		&& !thr_get_trx(thr)->in_rollback)) {
-
+		&& !dfield_is_ext(dtuple_get_nth_field(
+					  new_entry,
+					  index->first_user_field())))) {
 		big_rec_vec = dtuple_convert_big_rec(index, update, new_entry, &n_ext);
 		if (UNIV_UNLIKELY(big_rec_vec == NULL)) {
 

storage/innobase/data/data0data.cc

@@ -640,9 +640,6 @@ dtuple_convert_big_rec(
 	if (entry->is_alter_metadata()) {
 		longest_i = index->n_uniq + DATA_ROLL_PTR;
 		dfield = dtuple_get_nth_field(entry, longest_i);
-#if 1 // FIXME: remove this
-		index->table->serialise_columns(heap, dfield);
-#endif
 		local_len = BTR_EXTERN_FIELD_REF_SIZE;
 		goto ext_write;
 	}

storage/innobase/row/row0upd.cc

@@ -1356,7 +1356,11 @@ row_upd_index_replace_metadata(
 			ut_ad(dfield_is_ext(dfield));
 			ut_ad(dfield_get_len(dfield) == FIELD_REF_SIZE);
 			ut_ad(!dfield_is_null(dfield));
-			dfield->data = uf->new_val.data;
+			dfield_set_data(dfield, uf->new_val.data,
+					uf->new_val.len);
+			if (dfield_is_ext(&uf->new_val)) {
+				dfield_set_ext(dfield);
+			}
 			continue;
 		}