golang/go · error

failed to parse any useful part of the trace: %v

Error message

failed to parse any useful part of the trace: %v

What it means

After the reader is created, `parseTrace` reads events until EOF, tracking `validEvents` — the count of events seen up to the last `EventSync`. If no sync point was ever reached (zero useful events), the trace is considered too corrupt/truncated to display and the accumulated per-event error `t.err` is surfaced. The viewer refuses to open rather than show misleading partial data.

Source

Thrown at src/cmd/trace/main.go:383

			validEvents = len(t.events)
			break
		}
		if err != nil {
			t.err = err
			break
		}
		t.events = append(t.events, ev)
		s.Event(&t.events[len(t.events)-1])

		if ev.Kind() == trace.EventSync {
			validBytes = cr.bytesRead.Load()
			validEvents = len(t.events)
		}
	}

	// Check to make sure we got at least one good generation.
	if validEvents == 0 {
		return nil, fmt.Errorf("failed to parse any useful part of the trace: %v", t.err)
	}

	// Finish off the parsedTrace.
	t.summary = s.Finalize()
	t.valid = validBytes
	t.size = size
	t.events = t.events[:validEvents]
	return t, nil
}

func (t *parsedTrace) startTime() trace.Time {
	return t.events[0].Time()
}

func (t *parsedTrace) endTime() trace.Time {
	return t.events[len(t.events)-1].Time()
}

View on GitHub (pinned to b6b368adc5)

Solutions

1. Re-record the trace ensuring the program reaches a clean `runtime/trace.Stop` (or defer it in main).
2. Check the program did not crash/OOM during tracing; capture to a local file rather than a pipe/network sink.
3. Ensure there is free disk space for the full trace write.
4. If you have a partial trace you genuinely want to inspect, try `-d=wire` to dump raw events directly, bypassing the sync requirement.

// re-record on parse failure
if _, err := parseTrace(f, sz); err != nil {
    log.Printf("trace unusable (%v); re-recording", err)
    rerecord()
}

When it happens

Trigger: A trace whose generation(s) all failed to parse before the first sync; a file truncated mid-generation before any generation closed; a trace from a crashing program that never flushed a complete generation; mixing bytes from two traces.

Common situations: Program crashed mid-trace before `trace.Stop` flushed; trace captured over a pipe that broke early; disk-full during trace write; trace concatenation experiments producing a non-sync-prefixable stream.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• failed to create trace reader: %w
• no trace file supplied
• failed to read trace file: %w
• failed to stat trace file: %v
• unknown pprof type %s

AI-assisted analysis of golang/go@b6b368adc5 (2026-08-12). Data as JSON: /api/errors/f1693ed6e6d36118. Report an issue: GitHub.