vitessio/vitess · error

failed to instantiate throttler

Error message

failed to instantiate throttler: %v

What it means

The binlog player (filtered replication / vreplication player) creates an internal throttler to cap TPS and replication lag before applying events. If throttler.New fails (invalid settings), applyEvents returns this wrapped error and the player stops.

Solutions

1. Validate the binlog player settings (MaxTPS, MaxReplicationLag) in the VReplication workflow spec and correct invalid values
2. Read the inner error (%v) — it names the exact throttler validation failure
3. Update the workflow via vtctld (UpdateVReplicationWorkflow) with fixed throttler parameters
4. If using custom code, pass valid non-negative MaxTPS/MaxReplicationLag

if settings.MaxTPS < 0 || settings.MaxReplicationLag < 0 {
    return fmt.Errorf("invalid throttler settings: MaxTPS=%d MaxReplicationLag=%d", settings.MaxTPS, settings.MaxReplicationLag)
}

err := blp.ApplyBinlogEvents(ctx)
if err != nil && strings.Contains(err.Error(), "failed to instantiate throttler") {
    // correct blpSettings and re-create the binlog player
}

When it happens

Trigger: ApplyBinlogEvents -> applyEvents with blpSettings whose MaxTPS or MaxReplicationLag values are invalid/nonsensical, causing throttler.New to return an error.

Common situations: Bad vr_cluster / BinlogSource settings in a VReplicationWorkflow spec (e.g. malformed stopAtCopy or throttler options), operator passing zero/negative throttler parameters programmatically.

Related errors

• error reading VReplication settings
• error updating time throttled
• failed to parse options column
• failed to process config options
• failed to update throttler

AI-assisted analysis of vitessio/vitess@01a25a7d17 (2026-09-01). Data as JSON: /api/errors/bfb8716869858735. Report an issue: GitHub.

Appendix: source

Thrown at go/vt/binlog/binlogplayer/binlog_player.go:296

func (blp *BinlogPlayer) applyEvents(ctx context.Context) error {
	// Read starting values for vreplication.
	settings, err := ReadVRSettings(blp.dbClient, blp.uid)
	if err != nil {
		log.Error(fmt.Sprint(err))
		return err
	}

	blp.position = settings.StartPos
	blp.stopPosition = settings.StopPos
	t, err := throttler.NewThrottler(
		fmt.Sprintf("BinlogPlayer/%d", blp.uid),
		"transactions",
		1, /* threadCount */
		settings.MaxTPS,
		settings.MaxReplicationLag,
	)
	if err != nil {
		err := fmt.Errorf("failed to instantiate throttler: %v", err)
		log.Error(fmt.Sprint(err))
		return err
	}
	defer t.Close()

	// Log the mode of operation and when the player stops.
	if len(blp.tables) > 0 {
		log.Info(fmt.Sprintf("BinlogPlayer client %v for tables %v starting @ '%v', server: %v", blp.uid,
			blp.tables,
			blp.position,
			blp.tablet))
	} else {
		log.Info(fmt.Sprintf("BinlogPlayer client %v for keyrange '%v-%v' starting @ '%v', server: %v", blp.uid,
			hex.EncodeToString(blp.keyRange.GetStart()),
			hex.EncodeToString(blp.keyRange.GetEnd()),
			blp.position,
			blp.tablet))
	}

View on GitHub (pinned to 01a25a7d17)