best db schema for time series data?

Hi,

I have to collect lots of prices from web sites and keep track of their
changes. What is the best option?

1) one 'price' row per price change:

    create table price (
        id_price primary key,
        id_product integer references product,
        price integer
    );

2) a single 'price' row containing all the changes:

    create table price (
        id_price primary key,
        id_product integer references product,
        price integer[] -- prices are 'pushed' on this array as they change
    );

Which is bound to give the best performance, knowing I will often need
to access the latest and next-to-latest prices?

Thanks,