Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!utgpu!water!watmath!clyde!cbosgd!ucbvax!carleton.EDU!LLACROIX From: LLACROIX@carleton.EDU.UUCP Newsgroups: comp.os.vms Subject: re: file system caches Message-ID: <8707072246.AA11663@ucbvax.Berkeley.EDU> Date: Mon, 6-Jul-87 23:14:00 EDT Article-I.D.: ucbvax.8707072246.AA11663 Posted: Mon Jul 6 23:14:00 1987 Date-Received: Fri, 10-Jul-87 03:30:05 EDT Sender: daemon@ucbvax.BERKELEY.EDU Distribution: world Organization: The ARPA Internet Lines: 20 (Gerard K. Newman recently asked why his directory cache performance decreased when the cache size was _increased_.) There is probably a good, understandable reason for this, and I'll let someone else give the "correct" answer :-) Off the top of my head, I have two comments which may be relevant. First, how controled was your experiment when you were measuring the performance? If you just monitored normal activity, the activity mix may have changed and _that_ could explain the reduced cache performance. Second, and much more obscure, it is known that certain cache algorithms (such as FIFO) _can_ have decreased performance for a fixed sequence of requests when the cache size in increased. I don't know the details but I have seen a small example, considering cache sizes of 3 and 4. Intuitively, I would expect the chances of running into this in the real-life case of your directory cache to be extremely small. Intuitively, I wouldn't have expected the anomaly to exist, either. - Les LaCroix (csnet: llacroix@carleton.edu)