public static boolean isPdx(byte[] valueBytes) {
    if (valueBytes == null || valueBytes.length < 1) {
      return false;
    }
    return valueBytes[0] == DSCODE.PDX.toByte();
  }
Make sure we have room to add a VLF offset.
geode-core/src/main/java/org/apache/geode/pdx/internal/PdxWriterImpl.java