mlflow/mlflow · warning

Unable to derive UC location string for ${JSON.stringify(thi

Error message

Unable to derive UC location string for ${JSON.stringify(this._location)}; skipping trace registration.

What it means

The UC table trace exporter registers traces against a Unity Catalog location. getUcLocationString() failed to derive a location string from this._location, so trace registration is skipped and this warning is logged. Without a valid location string the exporter cannot construct the v4 trace ID or the destination UC table, so exporting traces from this span processor is impossible.

Source

Thrown at libs/typescript/core/src/exporters/uc_table.ts:62

  private _location: UnityCatalogLocation;

  constructor(exporter: SpanExporter, location: UnityCatalogLocation) {
    this._exporter = exporter;
    this._location = location;
  }

  onStart(span: OTelSpan, _parentContext: Context): void {
    const otelTraceId = span.spanContext().traceId;

    if (!span.parentSpanContext?.spanId) {
      // Root span: build the V4 trace ID and TraceInfo for this trace.
      const traceLocation: TraceLocation = {
        type: TraceLocationType.UC_TABLE_PREFIX,
        ucTablePrefix: { ...this._location },
      };
      const locationString = getUcLocationString(traceLocation);
      if (!locationString) {
        console.warn(
          `Unable to derive UC location string for ${JSON.stringify(this._location)}; skipping trace registration.`,
        );
        return;
      }

      const traceId = constructTraceIdV4(locationString, otelTraceId);

      const traceMetadata: Record<string, string> = {
        [TraceMetadataKey.SCHEMA_VERSION]: '4',
      };
      const ctxMetadata = getConfiguredTraceMetadata();
      if (ctxMetadata) {
        Object.assign(traceMetadata, ctxMetadata);
      }

      const tags: Record<string, string> = {};
      const ctxTags = getConfiguredTraceTags();
      if (ctxTags) {

View on GitHub (pinned to 6a27f2decc)

Solutions

1. Pass a complete UC location to the exporter, e.g. new MlflowUcTableSpanExporter({ catalog: 'main', schema: 'ml', table: 'otel_spans' }).
2. Log/inspect this._location at construction time and confirm all required UC parts are non-empty strings.
3. Resolve the configuration before constructing the exporter (await env/config loading) rather than passing a placeholder object.
4. Validate the location string renders correctly by calling getUcLocationString() yourself in a startup check.

Example fix

// before
const exporter = new MlflowUcTableSpanExporter({} as any);
// after
const exporter = new MlflowUcTableSpanExporter({ catalog: 'main', schema: 'monitoring', table: 'traces' });

function assertUcLocation(loc: unknown): asserts loc is { catalog: string; schema: string; table: string } {
  if (!loc || typeof loc !== 'object') throw new Error('UC location must be an object');
  const l = loc as Record<string, unknown>;
  for (const k of ['catalog', 'schema', 'table']) {
    if (typeof l[k] !== 'string' || !(l[k] as string).length) throw new Error(`UC location missing '${k}'`);
  }
}
assertUcLocation(location); // call before constructing the exporter

function isValidUcLocation(l: unknown): l is { catalog: string; schema: string; table: string } {
  return !!l && typeof l === 'object' &&
    ['catalog', 'schema', 'table'].every(k => typeof (l as any)[k] === 'string' && (l as any)[k].length > 0);
}

When it happens

Trigger: onStart is called with a TraceLocation whose ucTablePrefix (catalog/schema/table parts) is empty, malformed, or of an unsupported shape, causing getUcLocationString() to return undefined/null.

Common situations: Configuring MlflowUcTableSpanExporter with an incomplete { catalog, schema, table } object (missing fields or empty strings); constructing the exporter before config/env that supplies the UC table name is loaded; passing a location object with wrong property names.

Related errors

• INVALID_PARAMETER_VALUE
• UC volume path must be provided to save, log or load SparkML
• {e.message}. If you are trying to use the Model Registry in
• INVALID_PARAMETER_VALUE
• BAD_REQUEST

AI-assisted analysis of mlflow/mlflow@6a27f2decc (2026-08-29). Data as JSON: /api/errors/91422a30bcb46056. Report an issue: GitHub.