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		   B O S T O N   U N I V E R S I T Y
                                       
		      Computer Science Department
                                       
			  C O L L O Q U I U M
                                       
		       Wednesday February 15, 1995
                                       
				 3:00pm
		       (Coffee served at 2:30pm)
                                       
			 Seminar Room / MCS 135
                                       

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		Cache Structure in Large-Scale Object Systems
				       
				 Liuba Shrira
		       Laboratory for Computer Science
				     MIT
				       

   Cache structure can have an significant effect on the overall
   performance of a distributed system.  In a distributed object system,
   client caches managed on the basis of small granularity objects can
   provide better memory utilization then page-based caches.  However,
   object servers, unlike page servers, must perform additional disk reads.
   These installation reads are required to install modified objects onto
   their corresponding disk pages.  The opportunistic log is a new
   technique that significantly reduces the cost of installation reads.  It
   defers the installation reads, removing them from the modification
   commit path, and manages a large pool of pending installation reads that
   can be scheduled efficiently.

   Using simulations, we show that the opportunistic log substantially
   enhances the I/O performance of reliable storage servers.  An object
   server without the opportunistic log requires much better client caching
   to outperform a page server.  With an opportunistic log, only a small
   client cache improvement suffices.

   Our results imply that efficient scheduling of installation reads can
   substantially improve the performance of large-scale storage systems,
   and therefore introduce a new performance tradeoff between page-based
   and object-based architectures.
 
   (Joint work with James O'Toole)

Host: Prof. Abdelsalam Heddaya
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For colloquium info, including directions, see http://cs-www.bu.edu/colloquium
   For more information contact Prof. Mark Crovella <crovella@bu.edu>
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