apache/druid · error · UnsupportedOperationException (UOE)

resultFormat[ ] is not supported

Error message

resultFormat[%s] is not supported

What it means

ScanQueryEngine only implements the 'list' and 'compactedList' result formats in its iterator; any other value of resultFormat (including valueVector) is rejected with UOE. The format is set via the query's resultFormat property.

Solutions

1. Set resultFormat to "list" or "compactedList"
2. Remove the resultFormat property to use the default
3. Use the SQL/MSQ engine if vectorized output is required

Example fix

// before
{"queryType":"scan","resultFormat":"valueVector",...}
// after
{"queryType":"scan","resultFormat":"compactedList",...}

if (!"list".equals(fmt) && !"compactedList".equals(fmt)) {
  throw new IllegalArgumentException("resultFormat must be list or compactedList");
}

boolean supportedFormat(ScanQuery q) {
  return q.getResultFormat() == ScanQuery.ResultFormat.RESULT_FORMAT_LIST
      || q.getResultFormat() == ScanQuery.ResultFormat.RESULT_FORMAT_COMPACTED_LIST;
}

try {
  engine.process(query, segment, responseContext);
} catch (UnsupportedOperationException e) {
  // fall back to default resultFormat
}

When it happens

Trigger: Issuing a scan query with resultFormat set to an unsupported value such as "valueVector" against the native scan engine path that lacks support for it.

Common situations: Copy-pasting resultFormat from MSQ/SQL documentation into native scan queries; clients auto-setting resultFormat=valueVector expecting vectorized results; typos like "listx" caught elsewhere but custom formats failing here.

Related errors

• VALUE_VECTOR is not supported yet
• Cannot apply limit[ ] with offset[ ] due to overflow
• Cannot execute query with orderBy
• Cannot provide 'order' incompatible with 'orderBy'
• Column [ ] from 'orderBy' must also appear in 'columns'.

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/79de2c071c589db0. Report an issue: GitHub.

Appendix: source

Thrown at processing/src/main/java/org/apache/druid/query/scan/ScanQueryEngine.java:183

              @Override
              public ScanResultValue next()
              {
                if (!hasNext()) {
                  throw new NoSuchElementException();
                }
                if (hasTimeout && System.currentTimeMillis() >= timeoutAt) {
                  throw new QueryTimeoutException(StringUtils.nonStrictFormat("Query [%s] timed out", query.getId()));
                }
                final long lastOffset = offset;
                final Object events;
                final ScanQuery.ResultFormat resultFormat = query.getResultFormat();
                if (ScanQuery.ResultFormat.RESULT_FORMAT_COMPACTED_LIST.equals(resultFormat)) {
                  events = rowsToCompactedList();
                } else if (ScanQuery.ResultFormat.RESULT_FORMAT_LIST.equals(resultFormat)) {
                  events = rowsToList();
                } else {
                  throw new UOE("resultFormat[%s] is not supported", resultFormat.toString());
                }
                responseContext.addRowScanCount(offset - lastOffset);
                return new ScanResultValue(
                    segment.getId() == null ? null : segment.getId().toString(),
                    allColumns,
                    events,
                    rowSignatureBuilder.build()
                );
              }

              @Override
              public void remove()
              {
                throw new UnsupportedOperationException();
              }

              private List<List<Object>> rowsToCompactedList()
              {

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