An Experimental Study of Aging Influence on Query Cost Estimation

Abstract

Many update queries on a database can eventually degrade the structural efficiency of the database and result in lower performance. This phenomenon is called aging. On aged databases, conventional cost-based query optimizers could choose non-optimal query execution plan because they are not aging-aware and could not accurately estimate query execution cost.As a first step to build an aging-aware query optimizer, we experimentally examined the discrepancy between actual and estimated cost in order to investigate aging influence on the accuracy of cost estimation. The experimental result shows that aging could produce non-negligible cost estimation errors, up to 66.3%. The result indicates that a conventional query optimizer can fail to choose the optimal execution plan even for a simple query.