private void markVariableField() {
    if (!hasSeenFirstVlf) {
      hasSeenFirstVlf = true;
    } else {
      ensureVlfCapacity();
      vlfOffsets[vlfCount] = getCurrentOffset();
      vlfCount++;
    }
  }
This is required while writing the byte stream.

@param offsetCount Number of offsets to appended in this byte stream.
@param size Size of the byte stream (excluding DSCODE, length int and the offsets.)
@return size of each offset
geode-core/src/main/java/org/apache/geode/pdx/internal/PdxWriterImpl.java