3. A system comprising: one or more processors; and a non-transitory memory coupled to the processors comprising instructions executable by the processors, the processors operable when executing the instructions to: receive, from a client system of a first user, a search query requesting objects of a first object type, the search query comprising an inner query requesting objects of a second object type, wherein the requested objects are structured documents stored on a plurality of data stores storing objects of a plurality of object types, respectively, wherein each data store only stores objects of a single object type, and wherein each data store comprises an index server coupled to the data store for processing query requests for objects of the particular object type stored on the data store; retrieve, by an index server of a second data store that only stores objects of the second object type, identifiers of one or more objects of the second object type requested by the inner query using an inverted index of the second data store, wherein the index server of the second data store maintains one or more search indices of the objects of the second object type stored on the second data store, and wherein one of the search indices is the inverted index of the second data store; retrieve, by an index server of a first data store that only stores objects of the first object type, for each of the identified one or more objects of the second object type, identifiers of one or more objects of the first object type requested by the search query, the one or more objects of the first object type being identified using an inverted index of the first data store, wherein the index server of the first data store maintains one or more search indices of the objects of the first object type stored on the first data store, and wherein one of the search indices is the inverted index of the first data store; aggregate a plurality of search results responsive to the search query, each search result corresponding to an identified object of the first object type; and send, to the client system of the first user, one or more of the aggregated search results.
3. A system comprising: one or more processors; and a non-transitory memory coupled to the processors comprising instructions executable by the processors, the processors operable when executing the instructions to: receive, from a client system of a first user, a search query requesting objects of a first object type, the search query comprising an inner query requesting objects of a second object type, wherein the requested objects are structured documents stored on a plurality of data stores storing objects of a plurality of object types, respectively, wherein each data store only stores objects of a single object type, and wherein each data store comprises an index server coupled to the data store for processing query requests for objects of the particular object type stored on the data store; retrieve, by an index server of a second data store that only stores objects of the second object type, identifiers of one or more objects of the second object type requested by the inner query using an inverted index of the second data store, wherein the index server of the second data store maintains one or more search indices of the objects of the second object type stored on the second data store, and wherein one of the search indices is the inverted index of the second data store; retrieve, by an index server of a first data store that only stores objects of the first object type, for each of the identified one or more objects of the second object type, identifiers of one or more objects of the first object type requested by the search query, the one or more objects of the first object type being identified using an inverted index of the first data store, wherein the index server of the first data store maintains one or more search indices of the objects of the first object type stored on the first data store, and wherein one of the search indices is the inverted index of the first data store; aggregate a plurality of search results responsive to the search query, each search result corresponding to an identified object of the first object type; and send, to the client system of the first user, one or more of the aggregated search results. 17. The system of claim 3 , wherein the processors are further operable when executing the instructions to: access a social graph comprising a plurality of nodes and a plurality of edges connecting the nodes, each of the edges between two of the nodes representing a single degree of separation between them, the nodes comprising: a first node corresponding to the first user, wherein the first user is a user of an online social network; and a plurality of second nodes corresponding to a plurality of objects associated with the online social network, respectively.