SCALABLE TRANSACTION-BASED DATA REPOSITORY SERVICE

A reliable and scalable data repository service can be supporting cooperative transactions. In an example, multiple data producers may use the data repository service to upload data in one or more transactions. Data contained in one transaction may be treated as an atomic unit. In an embodiment, the data repository service manages multiple candidate transactions associated with an election transaction such that at most one candidate transaction may begin and/or commit a given time. During a commit of a candidate transaction, the data uploaded during the candidate transaction may become associated with the election transaction. The data repository service may maintain metadata associated with each of the candidate transactions. In response to a request for data associated with the election transaction, the metadata may be used, in conjunction with a user-specified isolation level, to locate the data uploaded some of the candidate transactions for the election transaction.