I understand that MySQL and others support large enough data for storing and retrieving. I am also aware of the open source projects such as hadoop and mapreduce etc.. (only their purpose and what they do).
EDIT: when do you bring down the concept of hadoop , pig, mapreduce etc to your application?. Should we use these software in the beginning of the project itself or can it be induced at a later stage after the database is increased to large size?. Any link will be appreciated.