vitessio/vitess · warning

failed to execute logEntry template: %v

Error message

failed to execute logEntry template: %v

What it means

showThrottlerLog renders each throttler log entry through logEntryTemplate; if template execution returns an error it panics. As with the header template, this should be impossible in normal operation and indicates the template and the Result/ColorLevel data struct are out of sync, or the response writer failed.

Source

Thrown at go/vt/throttler/throttlerlogz.go:167

		if stateGreater(r.NewState, state) {
			state = r.NewState
		}
		var colorLevel string
		switch state {
		case stateIncreaseRate:
			colorLevel = "low"
		case stateDecreaseAndGuessRate:
			colorLevel = "medium"
		case stateEmergency:
			colorLevel = "high"
		}
		data := struct {
			Result
			ColorLevel string
		}{r, colorLevel}

		if err := logEntryTemplate.Execute(w, data); err != nil {
			panic(fmt.Sprintf("failed to execute logEntry template: %v", err))
		}
	}

	logz.EndHTMLTable(w)

	// Print footer.
	count := len(results)
	var d time.Duration
	if count > 0 {
		d = results[0].Now.Sub(results[count-1].Now)
	}
	if err := logFooterTemplate.Execute(w, map[string]any{
		"Count":    count,
		"TimeSpan": fmt.Sprintf("%.1f", d.Minutes()),
	}); err != nil {
		panic(fmt.Sprintf("failed to execute logFooter template: %v", err))
	}
}

View on GitHub (pinned to 01a25a7d17)

Solutions

1. Align logEntryTemplate field references with the current Result struct
2. For streaming write failures, log and abort the response instead of panicking
3. Re-run throttlerlogz unit tests after any template or struct change

Example fix

// before
if err := logEntryTemplate.Execute(w, data); err != nil {
    panic(fmt.Sprintf("failed to execute logEntry template: %v", err))
}
// after
if err := logEntryTemplate.Execute(w, data); err != nil {
    log.Warnf("failed to execute logEntry template: %v", err)
    return
}

// verify template parses at startup
if err := logEntryTemplate.Execute(io.Discard, struct{ Result; ColorLevel string }{}); err != nil {
    return err
}

defer func() {
    if r := recover(); r != nil {
        log.Errorf("throttlerlogz entry render panic: %v", r)
        http.Error(w, "internal error", http.StatusInternalServerError)
    }
}()

When it happens

Trigger: Rendering /throttlerlogz when logEntryTemplate references fields missing from the anonymous struct{Result; ColorLevel string}, or the HTTP response write fails mid-stream (client disconnect).

Common situations: Forks/patches that changed Result fields without updating logEntryTemplate; client disconnection while streaming many entries.

Related errors

• failed to execute logHeader template: %v
• failed to Execute() template: %v
• failed to generate vtgate consul datacenter from template: %
• failed to parse vtgate FQDN template %s: %w
• failed to parse vtgate host address template %s: %w

AI-assisted analysis of vitessio/vitess@01a25a7d17 (2026-09-01). Data as JSON: /api/errors/59f6b435cf4e5a73. Report an issue: GitHub.