Data warehouses have evolved because, in order for businesses to remain
competitive in the marketplace, they need access to a wealth of information
to help them make the right business decisions. To assist with those decisions,
data may go back for many years and could entail keeping the details
of every item that a business ever sold. Performance optimizations for
update-centric OLTP systems are well understood; however, data warehouses,
being query-centric, have vastly different requirements, and a single
business intelligence query may need to retrieve and aggregate many records
from the warehouse.
