row_purge_parse_undo_rec(): Set node->ref for the metadata record

FIXME: This should apply to 10.3 as well. Write a test case for 10.3.

mysql-test/suite/innodb/r/instant_alter_crash.result

@@ -88,7 +88,7 @@ header=0x010000030074 (id=0x696e66696d756d00)
 header=0x010008030000 (id=0x73757072656d756d00)
 t2 clustered index root page(type 18):
 N_RECS=6; LEVEL=0
-header=0x01000003008f (id=0x696e66696d756d00)
+header=0x01000003008f (id=0x0000000000000000)
 header=0x3000100c00d4 (id=0x80000000,
  DB_TRX_ID=0x000000000000,
  DB_ROLL_PTR=0x80000000000000,
@@ -118,7 +118,7 @@ header=0x0000380b0074 (id=0x8000015b,
  DB_ROLL_PTR=0x80000000000000,
  c2=0x8000814d,
  c3=0x206574206d616c6f72756d)
-header=0x070008030000 (id=0x73757072656d756d00)
+header=0x070008030000 (id=0x000000000000000100)
 UNLOCK TABLES;
 DELETE FROM t2;
 InnoDB		0 transactions not purged

mysql-test/suite/innodb/t/instant_alter_crash.test

@@ -141,11 +141,6 @@ for (my $offset= 0x65; $offset;
 	for (my $i= 0; $i < $n_fields; $i++) {
 	    my $end= unpack("n", substr($page, $offset-8-2*$i, 2));
 	    print ",\n " if $i;
-	    # Work around a bug in the code!
-            if (!(~unpack("C",substr($page,$offset-6,1)) & 0x30)) {
-	        substr($page,$offset+$start,6) = pack("x[6]") if $i == 1;
-	        substr($page,$offset+$start,7) = pack("Cx[6]",128) if $i == 2;
-	    }
 	    if ($i > 2 && !(~unpack("C",substr($page,$offset-6,1)) & 0x30)) {
 		if ($i == 3) {
 		    print "BLOB=";

storage/innobase/row/row0purge.cc

@@ -1148,10 +1148,13 @@ row_purge_parse_undo_rec(
 	/* Read to the partial row the fields that occur in indexes */
 
 	if (!(node->cmpl_info & UPD_NODE_NO_ORD_CHANGE)) {
+		ut_ad(!(node->update->info_bits & REC_INFO_MIN_REC_FLAG));
 		ptr = trx_undo_rec_get_partial_row(
 			ptr, clust_index, node->update, &node->row,
 			type == TRX_UNDO_UPD_DEL_REC,
 			node->heap);
+	} else if (node->update->info_bits & REC_INFO_MIN_REC_FLAG) {
+		node->ref = &trx_undo_metadata;
 	}
 
 	return(true);