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Date: Fri, 13 Dec 1996 17:06:26 GMTServer: NCSA/1.5Content-type: text/htmlLast-modified: Wed, 30 Oct 1996 19:01:59 GMTContent-length: 3111<HTML><HEAD><TITLE>DEVise Performance</TITLE></HEAD><BODY><H1>Performance</H1>DEVise is designed to handle large amounts of data from the ground up.The following discussion assumes that the reader is already familiarwith the <!WA0><!WA0><!WA0><!WA0><!WA0><!WA0><A href="http://www.cs.wisc.edu/~devise/devise/model.html">model of visualization</A>. DEViseaddresses performance as follows:<UL><LI><!WA1><!WA1><!WA1><!WA1><!WA1><!WA1><A href="#IO">I/O</A><LI><!WA2><!WA2><!WA2><!WA2><!WA2><!WA2><A href="#Mapping">Mapping</A><LI><!WA3><!WA3><!WA3><!WA3><!WA3><!WA3><A href="#Drawing">Drawing GData</A><LI><!WA4><!WA4><!WA4><!WA4><!WA4><!WA4><A href="#Interface">User Interface</A><LI><!WA5><!WA5><!WA5><!WA5><!WA5><!WA5><A href="#Program">Program Design</A></UL><A name="IO"><H2>I/O</H2></A>Minimizing the amount of accesses to disk is the goal of improving I/Operformance. It is not practical to rely on the virtual memory of aworkstation because thrashing readily occurs when the amount of datais large. DEVise addresses I/O performance as follows:<UL><LI>Buffer Manager: Ranges (not pages) of TData andGData are retained in memory buffers. A non-LRU replacementpolicy is used.<LI>Query processor: decides which ranges of GData are accessed. It performs binary search for GData when sorted on the X attribute.It fetches those GData in overlapping views only once. When the user is idle,it converts TData into GData in the background. It can alsopotentially incorporate prefetching and indexing.<LI>mapping: reduces storage overhead by storing only those GDataattributes that change at run time.</UL><A name="Mapping"><H2>Mapping</H2></A>Mapping performance is improved as follows:<UL><LI>compiled mapping: reduces time/space at run time. The timeis reduced through compilation. The space is reduced throughstoring only those GData attributes that change at run time.<LI>Caching: caching GData in the buffer and on disk eliminates the need toperform mapping.</UL><A name="Drawing"><H2>Drawing GData</H2></A>Drawing performance is improved as follows:<UL><LI>GData that overlap are drawn just once.<LI>At low resolutions, GData are drawn as pixels. This is cheaper thandrawing complex shapes.</UL><A name="Interface"><H2>User Interface</H2></A>The user interface is designed to minimize the user response time:<UL><LI>The layout mode (See <!WA6><!WA6><!WA6><!WA6><!WA6><!WA6><A href="http://www.cs.wisc.edu/~devise/devise/visualQuery.html">visual query</A>.)increases response time by not drawing the GData when the userconstructs a visual query.<LI>Coming up for air: The query processor checks user actions periodically,possibly aborting existing queries to act upon new user commands.</UL><A name="Program"><H2>Program Design</H2></A>The implementation is structured for performance as follows:<UL><LI>Query abort: The ability to abort query throughout the designof the DEVise components allows the user interface to abandonexisting updates to act on new user commands.<LI>Batching: Transferring GData in batches instead of oneat a time reduces time spent in function calls.<LI>Minimizing number of objects: In an object oriented environment,everything is instantiated as an object. This is not done in DEVise, whichmust handle large numbers of records. Instantiating every input record as a shape object impedes performance. </UL></BODY></HTML>⌨️ 快捷键说明
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