I would caution against speculating about TSM database cache algorithms and BUFPoolsize value effects without supporting evidence. I would not expect its use of database records in memory to be substantially different than its indexing of records on disk, where I doubt that there would be a lot of "searching through memory".
Performance degradation with elevated BUFPoolsize levels is traditionally due to paging, as the TSM Performance Tuning Guide explains in its recommendations for values. (There are supplementary Technotes.) Operating system memory utilization is always a complex topic, which also changes as each OS evolves. Having a large amount of memory is wonderful; but one can't assume that the OS is going to apportion its utilization as we might expect. An OS typically computes sizes for various reserved areas at boot time, according to the ingredients defined to the system, and hardware discovered. The amount of memory left for application use may be substantially less than total memory. Environmental values under which a server process is started can also limit how much memory it is allowed to work with. So, be sure to pursue analysis where you perceive performance characteristics you don't expect. Enlist your OS specialist as necessary. Richard Sims at Boston University
