thanos-io/thanos · error

empty data field in TSDB status response

Error message

empty data field in TSDB status response

What it means

Client TSDB status retrieval (TSDBStatus/related /prom_status_tsdb call) performs a 2xx GET and decodes into a wrapper struct with a Data field. If the Prometheus API answered successfully but the JSON `data` field is null/absent, the client returns this sentinel error rather than returning a nil pointer.

Solutions

1. Check the Prometheus version supports /api/v1/status/tsdb and upgrade if older.
2. Ensure the correct API path/flags (e.g. admin APIs enabled) on the target Prometheus.
3. Inspect the raw response body with curl to see whether data is null and why.
4. Handle the error in callers (e.g. skip TSDB stats collection for that endpoint) instead of crashing.

Example fix

// before
if v.Data == nil {
	return nil, errors.New("empty data field in TSDB status response")
}

// after (caller-side tolerant handling)
data, err := client.TSDBStatus(ctx)
if err != nil {
	if strings.Contains(err.Error(), "empty data field") {
		level.Warn(logger).Log("msg", "TSDB status unavailable for endpoint; skipping")
		return nil, nil
	}
	return nil, err
}

type tsdbStatusWrapper struct { Data json.RawMessage `json:"data"` }
func hasData(w tsdbStatusWrapper) bool { return len(w.Data) > 0 && string(w.Data) != "null" }

data, err := client.TSDBStatus(ctx)
if err != nil {
	level.Warn(logger).Log("msg", "TSDB status unavailable, continuing without it", "err", err)
	data = nil // degrade gracefully
}

When it happens

Trigger: c.get2xxResultWithGRPCErrors succeeds but v.Data == nil — the queried Prometheus version does not populate data for the TSDB status endpoint (older versions, API disabled via --web.enable-admin-api semantics, or an incompatible proxy stripping the payload).

Common situations: Running against an old Prometheus lacking the /api/v1/status/tsdb endpoint shape; admin APIs disabled; intermediary (sidecar/proxy) returning {"status":"success"} with no data.

Understand the failure class

Background: "empty response", "returned no data", "empty embeddings": what HTTP 200-with-empty-body errors mean across libraries — this error's family across 36 libraries.

Related errors

• failed to get prometheus version
• ErrFlagEndpointNotFound
• failed to create matchers cache
• failed to validate prometheus flags
• initial external labels query

AI-assisted analysis of thanos-io/thanos@35b8b99117 (2026-09-07). Data as JSON: /api/errors/7f0fd3576d57e1f9. Report an issue: GitHub.

Appendix: source

Thrown at pkg/promclient/promclient.go:983

	q := u.Query()
	if len(matchers) > 0 {
		q.Add("match[]", storepb.PromMatchersToString(matchers...))
	}
	if limit > 0 {
		q.Add("limit", strconv.Itoa(limit))
	}
	u.RawQuery = q.Encode()

	var v struct {
		Data *statuspb.TSDBStatisticsEntry `json:"data"`
	}
	if err := c.get2xxResultWithGRPCErrors(ctx, "/prom_status_tsdb HTTP[client]", &u, &v); err != nil {
		return nil, err
	}

	if v.Data == nil {
		return nil, errors.New("empty data field in TSDB status response")
	}
	return v.Data, nil
}

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