Database System Concepts
Database System Concepts
7th Edition
ISBN: 9789332901384
Author: Henry F. Korth & S. Sudarshan Abraham Silberschatz
Publisher: MCGRAW-HILL HIGHER EDUCATION
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Chapter 14, Problem 8PE

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Secondary B+-tree:

  • Secondary B+-tree is constructed on a relation r with nr tuples.
  • The cost of building the tree index when one record is inserted at a time with the given assumptions.
  • The cost of insertion is the sum of below costs:
  • The cost to locate the page number of the requisite leaf node. In case of insertions this cost may vary as the non-leaf nodes are already in memory.
  • The cost to read one random disk access after reaching the leaf level.
  • The cost to update is also one random disk access.
  • The cost to write one page.
  • Not that if a node split occurs due to insertion the cost increases by an extra page write.
  • Now, in the worst scenario, each leaf node is just half filled. So, the number of splits is given by 2×(nr/f).
  • So, the total cost is maximum of either of these two values;
    • (2×nr) random disk access, or
    • (nr+2×(nr/f)) page writes.
  • Here, the cost of page writes is assumed to be negligible. So, the cost of random disk access is more.
  • So, substitute the given values in above in the above formula to get;
    • (2×nr) random disk access
    • =2×10000000×10×(1/1000)sec
    • =200000sec
    • 55.5hours
  • first sort the file in ascending order using the function which is assumed to be available.
  • Now, for each pair of value and pointer from the file call the insert-in-leaf function.
  • In insert-in-leaf function;
    • Check if the tree is empty, if yes, this is the first root node to be inserted. If it is considered as “L”.
    • Otherwise, since the values are sorted so insertion will occur in the last leaf node. So, transverse the leaf node to get the last leaf node.
    • Check if this node “L” is full or not. If not, insert the given value and pointer pair at the first available location is node “L”.
    • If this node is full, split it. In this case,
      • Create a leaf node and assume it as “L1”.
      • Set the pointer in node “L” to this node “L1”.
      • Initialize “K1” to the last value from nodes chain “L”.
      • Call the insert_in_parent function with desired values to insert this node in the parent...

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