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This paper deals with buffer management for tree-based access-path structures in real-time database system kernels. A predictable and efficient buffer replacement strategy for B- and B/sup +/-trees is introduced. The strategy called LC (Level Control) uses the structural information known about the trees and the tree search to determine a node to be replaced. The basic idea is to use the level of a node as replacement criteria. This allows a certain prediction of buffer hits and misses for tree search operations, even if the item's value searched for is unknown. A small prediction interval can be calculated for search operations and a larger interval for update operations. Simulations show the correctness of these calculations and the efficiency of LC for B- and B/sup +/-trees compared to common other replacement strategies.