apache/druid · info

Segment id [ ] is unknown

Error message

Segment id [%s] is unknown

What it means

GET /druid/coordinator/v1/datasources/{dataSourceName}/segments/{segmentId} looks up the segment by trying all possible parsings of the segment identifier. If no parsing corresponds to a served/known segment, it logs this warning and returns HTTP 204. It means the segment id doesn't match any segment the cluster knows about in that datasource.

Solutions

1. Verify the segment id format `datasource_start_end_version_partition` and the datasource name in the URL
2. List actual segments via GET /druid/coordinator/v1/datasources/{ds}/segments to get a valid id
3. Treat HTTP 204 as 'segment not found' and skip rather than retrying

Example fix

// before
GET /druid/coordinator/v1/datasources/wikipedia/segments/wikipedia_2020-01-01T00:00:00.000Z_2020-02-01T00:00:00.000Z_2020
// after (valid id from segments listing)
GET /druid/coordinator/v1/datasources/wikipedia/segments/wikipedia_2020-01-01T00:00:00.000Z_2020-01-02T00:00:00.000Z_2020-06-01T12:00:00.000Z_1

final List<String> ids = listSegments(dsName); if (!ids.contains(segmentId)) { skip lookup; }

boolean matchesKnownSegment(String id, Pattern p) { return id != null && p.matcher(id).matches(); } // ^ds_(\d{4}-\d{2}-\d{2}T..Z_){3}[0-9]+$

final Response r = client.target(segUrl).request().get(); if (r.getStatus() == 204) { LOG.info("segment {} unknown; skipping", segmentId); return Optional.empty(); }

When it happens

Trigger: getServedSegment() called with a segmentId string that cannot be parsed into a known SegmentId for the datasource — misspelled id, segment already killed, wrong datasource in the path, or segment never loaded.

Common situations: Querying for a segment id taken from old logs after it was killed; typos or truncated segment ids in scripts; checking a segment on the wrong coordinator/datasource path.

Understand the failure class

Background: 'Could not be found', 'does not exist', 'not found in database': the resource-not-found family when an ID, slug, key, or URI lookup comes back empty — this error's family across 20 libraries.

Related errors

• Cannot find any supervisor with id
• Cannot find any task with id
• datasource[ ] not found
• No task information found for task with id
• Query [ ] was not found. The query details are no longer…

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/9974dbb297b01a08. Report an issue: GitHub.

Appendix: source

Thrown at server/src/main/java/org/apache/druid/server/http/DataSourcesResource.java:654

  @Produces(MediaType.APPLICATION_JSON)
  @ResourceFilters(DatasourceResourceFilter.class)
  public Response getServedSegment(
      @PathParam("dataSourceName") String dataSourceName,
      @PathParam("segmentId") String segmentId
  )
  {
    ImmutableDruidDataSource dataSource = getQueryableDataSource(dataSourceName);
    if (dataSource == null) {
      return logAndCreateDataSourceNotFoundResponse(dataSourceName);
    }

    for (SegmentId possibleSegmentId : SegmentId.iteratePossibleParsingsWithDataSource(dataSourceName, segmentId)) {
      Pair<DataSegment, Set<String>> retVal = getServersWhereSegmentIsServed(possibleSegmentId);
      if (retVal != null) {
        return Response.ok(ImmutableMap.of("metadata", retVal.lhs, "servers", retVal.rhs)).build();
      }
    }
    log.warn("Segment id [%s] is unknown", segmentId);
    return Response.noContent().build();
  }

  /**
   * @deprecated Use {@code OverlordDataSourcesResource#markSegmentAsUnused} instead.
   */
  @Deprecated
  @DELETE
  @Path("/{dataSourceName}/segments/{segmentId}")
  @Produces(MediaType.APPLICATION_JSON)
  @ResourceFilters(DatasourceResourceFilter.class)
  public Response markSegmentAsUnused(
      @PathParam("dataSourceName") String dataSourceName,
      @PathParam("segmentId") String segmentIdString
  )
  {
    final SegmentId segmentId = SegmentId.tryParse(dataSourceName, segmentIdString);
    if (segmentId == null) {

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