A method for processing data in the form of a stream of messages regarding, for example, stock price information, implemented using a computer system wherein the data may arrive at a rate faster than the computer system can process individual messages. Each message is tagged with a phase number as it arrives; only the data in the messages received at the end of a phase are stored in the computer system's database. Periodically, at the end of at least one phase and perhaps at the end of many phases depending on the rate messages are received, the computer queries its database to select information regarding the data. Algorithms, according to the present invention, allow the efficient selection of data by disregarding a portion of the information in some cases, and, in other cases, by finding the phase ranges wherein data messages overlap between phase ranges. In the former, data is lost; it the latter, data processing may be slowed. The selected information is then output.