There are five Classes
SpQuery Class is used to retrieve data
from a specific list.
SPSiteDataQuery: The SPSiteDataQuery Class is used to Query
data from multiple lists across different site in site collection
ContentIterator :Provide methods to iterate list items, sites to regulate the amount is of data that is transferred
CrossListQueryCache:Provides a highly scalable way to run site wide queries.
PortalSiteMapProvider: Management of the Sharepoint object Cache