prestodb/presto · error · PrestoException

PROMETHEUS_UNKNOWN_ERROR

PROMETHEUS_UNKNOWN_ERROR

Error message

Error reading metrics

What it means

The generic catch (IOException e) in fetchUri wraps any non-SSL IO failure while executing the HTTP request or reading the response body and rethrows it as PROMETHEUS_UNKNOWN_ERROR with the message 'Error reading metrics'. It is the catch-all for connection failures, socket timeouts, and body-read errors against the Prometheus API.

Source

Thrown at presto-prometheus/src/main/java/com/facebook/presto/plugin/prometheus/PrometheusClient.java:202

                }
            }
            else {
                response = httpClient.newCall(requestBuilder.build()).execute();
                if (response.isSuccessful() && response.body() != null) {
                    return response.body().bytes();
                }
            }
        }
        catch (SSLHandshakeException e) {
            throw new PrestoException(PROMETHEUS_SECURE_COMMUNICATION_ERROR, "An SSL handshake error occurred while establishing a secure connection. Try the following measures to resolve the error:\n\n" + "- Upload a valid SSL certificate for authentication\n- Verify the expiration status of the uploaded certificate.\n- If you are connecting with SSL, enable SSL on both ends of the connection.\n", e);
        }
        catch (SSLPeerUnverifiedException e) {
            throw new PrestoException(PROMETHEUS_SECURE_COMMUNICATION_ERROR, "Peer verification failed. These measures might resolve the issue \n" +
                    "- Add correct Hostname in the SSL certificate's SAN list \n" +
                    "- The certificate chain might be incomplete. Check your SSL certificate\n", e);
        }
        catch (IOException e) {
            throw new PrestoException(PROMETHEUS_UNKNOWN_ERROR, "Error reading metrics", e);
        }
        catch (NoSuchAlgorithmException e) {
            throw new PrestoException(PROMETHEUS_SECURE_COMMUNICATION_ERROR, "Requested cryptographic algorithm is not available", e);
        }
        catch (KeyStoreException e) {
            throw new PrestoException(PROMETHEUS_SECURE_COMMUNICATION_ERROR, "Keystore operation error", e);
        }
        catch (KeyManagementException e) {
            throw new PrestoException(PROMETHEUS_SECURE_COMMUNICATION_ERROR, "Key management operation error", e);
        }

        throw new PrestoException(PROMETHEUS_UNKNOWN_ERROR, "Bad response " + response.code() + response.message());
    }

    private Optional<String> getBearerAuthInfoFromFile()
    {
        return bearerTokenFile.map(tokenFileName -> {
            try {

View on GitHub (pinned to 55bb57d202)

Solutions

1. Confirm the Prometheus URL is reachable from the Presto coordinator: curl the connection-url + '/api/v1/query' path
2. Check Prometheus server logs and health endpoint (/../../-/healthy) for crashes or overload
3. Increase query timeouts (both Presto and Prometheus) and reduce the time range of the query
4. Inspect the wrapped cause (PrestoException's cause) for the concrete IOException — connect refused vs timeout vs reset points to different fixes

// Pre-flight check that Prometheus is reachable from the coordinator
curl -fsS --max-time 5 http://prometheus.example.com:9090/-/healthy

catch (PrestoException e) {
  if (PROMETHEUS_UNKNOWN_ERROR.equals(e.getErrorCode().getName()) && "Error reading metrics".equals(e.getMessage())) {
    // transient IO: backoff and retry, or surface connectivity guidance
    retryWithBackoff();
  } else throw e;
}

When it happens

Trigger: fetchUri (via fetchMetrics/PrometheusRecordSet) hitting a refused connection, DNS failure, connect/read timeout, or stream truncation while downloading query results from the Prometheus endpoint.

Common situations: Prometheus down or restarted; wrong host/port in connection-url; firewall or NetworkPolicy blocking coordinator→Prometheus traffic; Prometheus timing out on expensive instant/range queries; large query responses dropped.

Related errors

• Failed reading response from remote Presto server
• Error fetching next (attempts: %s, duration: %s)
• INVALID_ARGUMENTS
• PINOT_HTTP_ERROR
• PROMETHEUS_TABLES_METRICS_RETRIEVE_ERROR

AI-assisted analysis of prestodb/presto@55bb57d202 (2026-09-04). Data as JSON: /api/errors/67b68ecad3ada855. Report an issue: GitHub.