protected int smallestUpperBoundSlotFor(ByteBuffer idx, long target, IndexSearchType searchEntity) {
        return indexSlotRangeFor(idx, target, searchEntity, SearchResultType.SMALLEST_UPPER_BOUND);
    }
Find the smallest entry greater than or equal the target key or value. If none can be found, -1 is returned.
storage/src/main/java/org/apache/kafka/storage/internals/log/AbstractIndex.java