backup: generate backupmeta when backup empty.

pkg/task/backup.go

@@ -130,7 +130,7 @@ func RunBackup(c context.Context, g glue.Glue, cmdName string, cfg *BackupConfig
 	}
 	// nothing to backup
 	if ranges == nil {
-		return nil
+		return client.SaveBackupMeta(ctx, nil)
 	}
 
 	ddlJobs := make([]*model.Job, 0)

pkg/task/restore.go

@@ -161,6 +161,8 @@ func RunRestore(c context.Context, g glue.Glue, cmdName string, cfg *RestoreConf
 	// nothing to restore, maybe only ddl changes in incremental restore
 	if len(files) == 0 {
 		log.Info("all files are filtered out from the backup archive, nothing to restore")
+		// even nothing to restore, we show a success message since there is no failure.
+		summary.SetSuccessStatus(true)
 		return nil
 	}
 

tests/br_backup_empty/run.sh

@@ -0,0 +1,34 @@
+#!/bin/sh
+#
+# Copyright 2020 PingCAP, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+set -eu
+
+# backup empty.
+echo "backup start..."
+run_br --pd $PD_ADDR backup full -s "local://$TEST_DIR/empty" --ratelimit 5 --concurrency 4
+if [ $? -ne 0 ]; then
+    echo "TEST: [$TEST_NAME] failed on backup empty cluster!"
+    exit 1
+fi
+
+# restore empty.
+echo "restore start..."
+run_br restore full -s "local://$TEST_DIR/empty" --pd $PD_ADDR --ratelimit 1024
+if [ $? -ne 0 ]; then
+    echo "TEST: [$TEST_NAME] failed on restore empty cluster!"
+    exit 1
+fi
+
+echo "TEST: [$TEST_NAME] successed!"