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Diff for /pegasus/src/Pegasus/Repository/Attic/instances.txt between version 1.1 and 1.2

version 1.1, 2002/02/15 00:03:59 version 1.2, 2002/02/15 00:13:30
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 <h1>Synopsis</h1>  /** Instance Repository
  
 This file describes the algorithms and architecture of the instances  <h1>Synopsis</h1>
 repository (that part of the repository which deals with instances).      Describes the algorithms and architecture of the instances repository
       (that part of the repository which deals with instances).
  
 <h1>Layout</h1> <h1>Layout</h1>
  
 All files belonging the instance repository are stored under the  All files belonging to the instance repository are stored under the
 repository/instances directory. For each class two files are maintained: repository/instances directory. For each class two files are maintained:
 and index file (with a ".idx" extension) and an instance file which bears and index file (with a ".idx" extension) and an instance file which bears
 the name of the class whose instances it contains. For example, suppose the name of the class whose instances it contains. For example, suppose
 there is a class called "Zebra". Then two files are used to managed  there is a class called "Zebra". Then two files are used to manage its
 its instances:  instances:
  
     <pre>     <pre>
     repository/instances/Zerbra.idx (called the index file)      repository/instances/Zebra.idx (called the index file)
     repository/instances/Zerbra (called the instance file)      repository/instances/Zebra (called the instance file)
     </pre>     </pre>
  
 The first line of the index file indicates how many instances have been The first line of the index file indicates how many instances have been
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     </pre>     </pre>
  
 First notice that the dirty count is equal to two and that two entries are First notice that the dirty count is equal to two and that two entries are
 marked as deleted (these quantities will always be equal). This indicates  marked as deleted (these quantities must be equal). This indicates that the
 that the instance file has two instances which are no longer used. The space  instance file has two instances which are no longer used. The space used by
 used by these instances will be reclaimed during reorganization.  these instances will be reclaimed during reorganization.
  
 The layout of the instance file is trivial. Instances are always appended to The layout of the instance file is trivial. Instances are always appended to
 to the instance file. The instances are kept end-to-end in the file. to the instance file. The instances are kept end-to-end in the file.
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 <h1>Reorganization</h1> <h1>Reorganization</h1>
  
 To improve performance, reclamation of unused space in the instance file To improve performance, reclamation of unused space in the instance file
 (called gaps) is postponed until there are N gaps. Deletion and modification  (called gaps) is postponed until there are m gaps. Deletion and modification
 operations create gaps. A dirty-count is maintained in the index file as operations create gaps. A dirty-count is maintained in the index file as
 described above. When this dirty count reaches N, available space is reclaimed.  described above. When this dirty count reaches m, available space is reclaimed.
 Reorganization is expensive: the entire file must be rewritten. The time Reorganization is expensive: the entire file must be rewritten. The time
 complexity is O(n) where n is the number of instances in the file. By complexity is O(n) where n is the number of instances in the file. By
 postponing reorganization, the time complexity may be reduced to O(1). postponing reorganization, the time complexity may be reduced to O(1).
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     </ul>     </ul>
  
   */

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