Analysis of the Request Patterns to the NSSDC On - line Archive

The successful implementation of mass storage archives require careful attention to performance optimizations, to ensure that the system can handle the ooered load. However, performance optimizations require an understanding of user access patterns. Since on-line archives and digital libraries are so new, little information is available. has run an on-line mass storage archive of space data, the National Data Archive and Distribution Service (NDADS), since November 1991. A large worldwide space research community makes use of NSSDC, requesting more than 20,000 les per month. Since the initiation of their service, NSSDC has maintained log les which record all accesses the archive. In this report, we present an analysis of the NDADS log les, spanning a four year period (1992-1995). We analyze the log les and discuss several issues, including caching, reference patterns, changes in user interest, user characterization, clustering, and system loading.