row_undo_mod_clust(): Fix the trx_id_offset for the metadata record

storage/innobase/row/row0umod.cc

@@ -415,18 +415,31 @@ row_undo_mod_clust(
 			goto mtr_commit_exit;
 		}
 
+		ulint trx_id_offset = index->trx_id_offset;
 		ulint trx_id_pos = index->n_uniq ? index->n_uniq : 1;
-		ut_ad(index->n_uniq <= MAX_REF_PARTS);
-		/* Reserve enough offsets for the PRIMARY KEY and 2 columns
-		so that we can access DB_TRX_ID, DB_ROLL_PTR. */
-		ulint	offsets_[REC_OFFS_HEADER_SIZE + MAX_REF_PARTS + 2];
-		rec_offs_init(offsets_);
-		offsets = rec_get_offsets(
-			rec, index, offsets_, true, trx_id_pos + 2, &heap);
-		ulint len;
-		ulint trx_id_offset = rec_get_nth_field_offs(
-			offsets, trx_id_pos, &len);
-		ut_ad(len == DATA_TRX_ID_LEN);
+		if (trx_id_offset) {
+		} else if (rec_is_metadata(rec, *index)) {
+			ut_ad(!buf_block_get_page_zip(btr_pcur_get_block(
+							      &node->pcur)));
+			for (unsigned i = index->first_user_field(); i--; ) {
+				trx_id_offset += index->fields[i].fixed_len;
+			}
+		} else {
+			ut_ad(index->n_uniq <= MAX_REF_PARTS);
+			/* Reserve enough offsets for the PRIMARY KEY and
+			2 columns so that we can access
+			DB_TRX_ID, DB_ROLL_PTR. */
+			ulint	offsets_[REC_OFFS_HEADER_SIZE + MAX_REF_PARTS
+					 + 2];
+			rec_offs_init(offsets_);
+			offsets = rec_get_offsets(
+				rec, index, offsets_, true, trx_id_pos + 2,
+				&heap);
+			ulint len;
+			trx_id_offset = rec_get_nth_field_offs(
+				offsets, trx_id_pos, &len);
+			ut_ad(len == DATA_TRX_ID_LEN);
+		}
 
 		if (trx_read_trx_id(rec + trx_id_offset) == node->new_trx_id) {
 			ut_ad(!rec_get_deleted_flag(