A system, comprising: a plurality of data warehouses (120a, 120b); and a data warehouse manager configured to extract data sets from one or more data sources for storage in one or more of said plurality of data warehouses; wherein each of a subset comprising two or more of said plurality of data warehouses is configured to store a respective replica of a data set extracted by said data warehouse manager; wherein said data warehouse manager is further configured to allow a query dependent upon said data set to be evaluated by one of said subset of data warehouses before each respective replica of said data set has been stored to a corresponding data warehouse of said subset; wherein said data warehouse manager is further configured to store in an operations database identifying information corresponding to each data set stored within said plurality of data warehouses, wherein for said data set, said identifying information comprises respective identities of each of said subset of data warehouses and respective state information indicating whether said data set has been stored to a corresponding one of said subset of data warehouses; wherein said data warehouse manager is further configured to detect that said query does not depend on an update currently ongoing to a first data warehouse of said subset of data warehouses; wherein said data warehouse manager is further configured to determine that a second data warehouse of said subset of data warehouses has sufficient data to evaluate said query according to said respective state information, and to responsively convey said query to said second data warehouse of said subset for evaluation, wherein said warehouse manager determines that a data warehouse has sufficient data to evaluate a given query if it has a copy of each data set depended upon by the query and if each data set depended upon is not otherwise being updated by the update currently ongoing to the first data warehouse; and wherein said query is evaluated by the second data warehouse of said subset while said data set is being stored to the first data warehouse of said subset. a plurality of data warehouses (120a, 120b); and a data warehouse manager configured to extract data sets from one or more data sources for storage in one or more of said plurality of data warehouses; wherein each of a subset comprising two or more of said plurality of data warehouses is configured to store a respective replica of a data set extracted by said data warehouse manager; wherein said data warehouse manager is further configured to allow a query dependent upon said data set to be evaluated by one of said subset of data warehouses before each respective replica of said data set has been stored to a corresponding data warehouse of said subset; wherein said data warehouse manager is further configured to store in an operations database identifying information corresponding to each data set stored within said plurality of data warehouses, wherein for said data set, said identifying information comprises respective identities of each of said subset of data warehouses and respective state information indicating whether said data set has been stored to a corresponding one of said subset of data warehouses; wherein said data warehouse manager is further configured to detect that said query does not depend on an update currently ongoing to a first data warehouse of said subset of data warehouses; wherein said data warehouse manager is further configured to determine that a second data warehouse of said subset of data warehouses has sufficient data to evaluate said query according to said respective state information, and to responsively convey said query to said second data warehouse of said subset for evaluation, wherein said warehouse manager determines that a data warehouse has sufficient data to evaluate a given query if it has a copy of each data set depended upon by the query and if each data set depended upon is not otherwise being updated by the update currently ongoing to the first data warehouse; and wherein said query is evaluated by the second data warehouse of said subset while said data set is being stored to the first data warehouse of said subset.