An Adaptive Strategy for Load Sharing in Distributed Database Environment with Information Lags

In this paper we examine a strategy that addresses the effect of information lags on load sharing in a distributed database system. Because dynamic state information is not immediately available to the various sites, decisions that are naively made on the basis of currently available information will be nonoptimal. In this environment sites must decide whether to select alternative sites to process incoming transactions, given that the information on which the decision is based exhibits varying degrees of obsolescence. We present an adaptive strategy that (1) explicitly takes the obsolescence into account when making routing decisions and (2) weights older information less heavily than more up-to-date information. The performance of this strategy is studied in a distributed database environment exhibiting both different degrees of site-to-site obsolescence and differing degrees of database load at each site. The Adaptive strategy is found to be able to properly weight the impact of load distribution, transaction site affinity, and information lags in order to make a judicious load sharing decision. Transaction response time is compared with that achieved by a dynamic routing strategy that ignores the issue of information lags and with the response time achieved by two static routing algorithms.