9. A method comprising: receiving a query from a query source, the received query including a bucket id identifying a bucket within an object store; parsing the received query into a query parse tree; generating candidate query plans, each of the candidate query plans being semantically equivalent to the received query; evaluating the candidate query plans based upon a cost model, wherein the cost model considers statistical information associated with the bucket including a number of objects stored in the bucket; selecting one of candidate query plans based upon the cost model evaluation; retrieving a plurality of object ids and corresponding object metadata from the object store using the bucket id; generating a stream of tuples from the retrieved object ids and object metadata; filtering the stream of tuples according to predicates within the received query; projecting the stream of tuples according to a list of metadata keys within the received query to generate a query result set stream; and generating a response to the query source based upon the query result set stream.
9. A method comprising: receiving a query from a query source, the received query including a bucket id identifying a bucket within an object store; parsing the received query into a query parse tree; generating candidate query plans, each of the candidate query plans being semantically equivalent to the received query; evaluating the candidate query plans based upon a cost model, wherein the cost model considers statistical information associated with the bucket including a number of objects stored in the bucket; selecting one of candidate query plans based upon the cost model evaluation; retrieving a plurality of object ids and corresponding object metadata from the object store using the bucket id; generating a stream of tuples from the retrieved object ids and object metadata; filtering the stream of tuples according to predicates within the received query; projecting the stream of tuples according to a list of metadata keys within the received query to generate a query result set stream; and generating a response to the query source based upon the query result set stream. 12. The method of claim 9 wherein the received query includes a select clause comprising the list of metadata keys.