public OptionalLong firstSegmentBaseOffset() {
        return firstSegment().map(logSegment -> OptionalLong.of(logSegment.baseOffset()))
                .orElseGet(OptionalLong::empty);
    }
@return the base offset of the log segment associated with the smallest offset, if it exists
storage/src/main/java/org/apache/kafka/storage/internals/log/LogSegments.java