By | August 28, 2010

Objective of the Project:

The main objective of this project is to analyze the performance of DBMS(Database Management System) by tuning  database. The performance of DBMS is significantly affected when the key tuning parameters are altered. It is therefore important to identify only few important parameters and evaluate their effect on the system performance. It is also important to understand the range of the tuning parameters over which tuning is most effective

Page Replacement :

Once the main memory fills up a page must be swapped out to make room for any pages to be swapped in. This is known as page replacement process        .

The page-fault service routine will:

  • Find the location of the desired page on disk.
  • Either find a free frame or create a free frame by selecting a victim frame, writing it to disk, and up-dating the page and frame tables.
  • Read the desired page into the free frame.
  • Restart the process.

Page replacement requires two page transfers. One approach to reduce this overhead is by using a dirty bit in the page table. When a page is modified the dirty bit is set. Suppose a page fault occurs and a victim is selected. If the bit is not set there is no need to write the page to disk as there already exists the identical page on disk.

Demand Paging :

  • Frame-allocation algorithm: How many frames do we allocate to each process?
  • Page-replacement algorithm: How do we select the victim to be replaced?
  • Page-Replacement Algorithms :

The goal of the page-replacement algorithm is to minimize the page-fault rate. Different algorithms may be compared by computing the number of page faults on a particular reference string. Given the overhead of a page fault, small improvements in the page replacement algorithm will greatly improve the performance of the entire system.

Generally, increasing the number of frames reduces the number of page faults.

Graph of Pages Faults vs Frames

    FIFO Page Replacement Algorithm:

FIFO (First In First Out) algorithm is extremely simple. It removes the page with earliest creation time.

This can be implemented using a list. New pages are inserted at the head of the list, and the page at the tail is swapped out.

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