PERSISTENCE

• SEVERAL APPROACHES TO DELETION:
  
  
  • EXPLICIT DELETE OPERATION: DANGLING OID PROBLEM
    
    
    • MARK FOR DELETION - KEEP A REFERENCE COUNT - DO REAL DELETE ONLY WHEN COUNT IS ZERO
    
    
  • EXPLICIT DELETE OPERATION & FAULT ON DELETED OBJECT: FREELY ALLOW DELETION - REFERENCES TO DELETED OBJECT CAUSE FAULTS
    
    
    • METHODS & APPLICATIONS NEED PROVIDE FAULT HANDLING CODE
    • DELETED OBJECTS' OIDs CANNOT BE REUSED - NOT A PROBLEM
    
    
  • PROVIDE NO EXPLICIT DELETE OPERATION: PERSISTENT OBJECT IS "GARBAGE COLLECTED" WHEN IT IS NO LONGER REFERENCED
  
  

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Ugo O. Gagliardi
GSD-6306 Spring 2003-2004