presto-spi/src/main/java/io/prestosql/spi/block/VariableWidthBlock.java/VariableWidthBlock/getRegionSizeInBytes
class VariableWidthBlock:    @Override
    public long getRegionSizeInBytes(int position, int length)
    {
        return offsets[arrayOffset + position + length] - offsets[arrayOffset + position] + ((Integer.BYTES + Byte.BYTES) * (long) length);
    }