backup: set concurrency to 1 when ratelimit enabled

pkg/task/backup.go

@@ -170,6 +170,13 @@ func (cfg *BackupConfig) adjustBackupConfig() {
 	if cfg.Config.Concurrency > maxBackupConcurrency {
 		cfg.Config.Concurrency = maxBackupConcurrency
 	}
+	if cfg.RateLimit != unlimited {
+		// TiKV limits the upload rate by each backup request.
+		// When the backup requests are sent concurrently,
+		// the ratelimit couldn't work as intended.
+		// Degenerating to sequentially sending backup requests to avoid this.
+		cfg.Config.Concurrency = 1
+	}
 
 	if cfg.GCTTL == 0 {
 		cfg.GCTTL = utils.DefaultBRGCSafePointTTL

pkg/task/common.go

@@ -72,6 +72,8 @@ const (
 	defaultSwitchInterval       = 5 * time.Minute
 	defaultGRPCKeepaliveTime    = 10 * time.Second
 	defaultGRPCKeepaliveTimeout = 3 * time.Second
+
+	unlimited = 0
 )
 
 // TLSConfig is the common configuration for TLS connection.
@@ -155,7 +157,7 @@ func DefineCommonFlags(flags *pflag.FlagSet) {
 	flags.Uint(flagChecksumConcurrency, variable.DefChecksumTableConcurrency, "The concurrency of table checksumming")
 	_ = flags.MarkHidden(flagChecksumConcurrency)
 
-	flags.Uint64(flagRateLimit, 0, "The rate limit of the task, MB/s per node")
+	flags.Uint64(flagRateLimit, unlimited, "The rate limit of the task, MB/s per node")
 	flags.Bool(flagChecksum, true, "Run checksum at end of task")
 	flags.Bool(flagRemoveTiFlash, true,
 		"Remove TiFlash replicas before backup or restore, for unsupported versions of TiFlash")