A method comprising: receiving , by a request broker of a computer system, an inquiry requesting availability status of a specified item; determining , by the request broker of the computer system, that the inquiry is an availability type request; retrieving , by the request broker of the computer system from one or more of a plurality of in-memory database instances, summary data associated with the specified item from a summary data structure stored in a memory of the computer system wherein the summary data structure is shared among two or more availability servers and one or more scheduling servers using said one or more in-memory database instances, the summary data structure being partitioned between the two or more availability servers, such that each of the two or more availability servers is assigned to different partitions of the summary data structure; determining , by the request broker of the computer system by evaluating routing rules, which of the two or more availability servers is assigned to the summary data associated with the specified item; forwarding , by the request broker of the computer system, the inquiry to the assigned availability server; determining , by said assigned availability server, availability data for the specified item based upon the summary data; and sending , by the request broker of the computer system, an inquiry response indicating the availability of the specified item based upon the determined availability data; wherein the operations performed by the two or more availability servers may read but not write to the summary data and the operations performed by the one or more scheduling servers may read and/or write to the summary data; wherein the plurality of in-memory database instances are distributed between the request broker of the computer system and the one or more scheduling servers. receiving , by a request broker of a computer system, an inquiry requesting availability status of a specified item; determining , by the request broker of the computer system, that the inquiry is an availability type request; retrieving , by the request broker of the computer system from one or more of a plurality of in-memory database instances, summary data associated with the specified item from a summary data structure stored in a memory of the computer system wherein the summary data structure is shared among two or more availability servers and one or more scheduling servers using said one or more in-memory database instances, the summary data structure being partitioned between the two or more availability servers, such that each of the two or more availability servers is assigned to different partitions of the summary data structure; determining , by the request broker of the computer system by evaluating routing rules, which of the two or more availability servers is assigned to the summary data associated with the specified item; forwarding , by the request broker of the computer system, the inquiry to the assigned availability server; determining , by said assigned availability server, availability data for the specified item based upon the summary data; and sending , by the request broker of the computer system, an inquiry response indicating the availability of the specified item based upon the determined availability data; wherein the operations performed by the two or more availability servers may read but not write to the summary data and the operations performed by the one or more scheduling servers may read and/or write to the summary data; wherein the plurality of in-memory database instances are distributed between the request broker of the computer system and the one or more scheduling servers. <EOS>