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    Presentation2 Presentation2 Presentation Transcript

    • Making the main memory of acluster of computers look as thoughit is a single memory with a singleaddress space.Then can use shared memoryprogramming techniques.
    •  System scalable Hides the message passing – do not explicitlyspecific sending messages between processesSimple extensions to sequential programmingCan handle complex and large data bases withoutreplication or sending the data to processes
    • May incur a performance penaltyMust provide for protection against simultaneousaccess to shared dataLittle programmer control over actual messagesbeing generatedPerformance of irregular problems in particular maybe difficult
    • •Special network interfaces and cache•Modifying the OS Kernel•Adding a software layer between the operatingsystem and the application – most convenientway for teaching purposes
    • •Page based – using the system’s virtualmemory•Shared variable approach – using routines toaccess shared variables•Object based – shared data within collectionof objects. Access to shared data through objectoriented discipline
    • • Easy to do• Can sit on top of message-passing software such as MPI
    • • Managing shared data –reader/writer policies• Timing issues – relaxingread/write orders
    • • Single reader/single writer policy – simple to dowith centralized servers• Multiple reader/single writer policy – again quitesimple to do• Multiple reader/multiple writer policy - tricky