The problem of buffer management in database management systems is concerned with the 
efficient main memory allocation and management for answering database queries. Previous 
works on buffer allocation are based either exclusively on the availability of buffers at 
runtime or on the access patterns of queries. In this paper, we first propose a unified 
approach for buffer allocation in which both of these considerations are taken into account. 
Our approach is based on the notion of marginal gains which specify the expected reduction 
in page faults by allocating extra buffers to a query. Then, we extend this approach to 
support adaptable buffer allocation. An adaptable buffer allocation algorithm automatically 
optimizes itself for the specific query workload. To achieve this adaptability, we propose 
using run-time information, such as the load of the system, in buffer allocation decisions. 
Our approach is to use a simple queueing model to predict whether a buffer allocation will 
improve the performance of the system. Thus, this paper provides a more theoretical basis 
for buffer allocation. Simulation results show that our methods based on marginal gains and 
our predictive methods consistently outperform existing allocation strategies. In addition, 
the predictive methods have the added advantage of adjusting their allocation to changing 
workloads.