apache/druid · error · IllegalStateException

Unexpected end of field

Error message

Unexpected end of field

What it means

addStringsToList expects to eventually read the row terminator byte marking the end of the field. If the loop consumes all values without seeing a terminator, the field is truncated relative to its expected layout and "Unexpected end of field" is thrown. Like the overrun check, it protects against corrupt or misaligned frame data.

Solutions

1. Re-run the query or re-read the frame from source to replace the truncated data.
2. Validate frame offsets/lengths when slicing frame partitions before reading fields.
3. Match reader/writer Druid versions and frame format.

try {
  reader.readStringsFromMemory(memory, position, limit, list);
} catch (IllegalStateException e) {
  if (e.getMessage().equals("Unexpected end of field")) {
    throw new CorruptFrameException("Truncated frame field; re-fetch frame", e);
  }
  throw e;
}

When it happens

Trigger: Decoding a string field where the declared field region ends (values loop exits) without a ROW_TERMINATOR byte — truncated frames, wrong length passed in, or offset pointing into the middle of a field.

Common situations: Frames sliced/paginated incorrectly before deserialization; reading a frame at a stale or partial offset (e.g. from durable storage that was truncated); version skew in frame serialization.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

• Invalid value start byte
• Value overrun
• A-Not-B requires at least 1 sketch
• Access-Check-Result
• Action [ ] failed for worker [ ] with status ( )

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/f6bece0b4f0225d5. Report an issue: GitHub.

Appendix: source

Thrown at processing/src/main/java/org/apache/druid/frame/field/StringFieldReader.java:604

              final ByteBuffer buf = FrameReaderUtils.readByteBuffer(memory, position, len);
              list.add(buf);

              position += len;

              break;
            }
          }

          break;

        default:
          throw new ISE("Invalid value start byte [%s]", kind);
      }
    }

    if (!rowTerminatorSeen) {
      throw new ISE("Unexpected end of field");
    }
    return isEffectivelyNull;
  }
}

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