on the tree, sequentiality is increasingly lost, and sequential access has towait for disk seeks increasingly often.a.One way to solve this problem is to rebuild the index to restoresequentiality.b.i.In the worst case eachn-block unit and each node of the B+-treeis half filled. This gives the worst case occupancy as 25 percent.ii.No. While splitting then-block unit the firstn/2 leaf pages areplaced in onen-block unit, and the remaining in the secondn-block unit. That is, everyn-block split maintains the order. Hence,the nodes in then-block units are consecutive.iii.In the regular B+-tree construction, the leaf pages might not besequential and hence in the worst case, it takes one seek per leafpage. Using the block at a time method, for eachn-node block,we will have at leastn/2 leaf nodes in it. Eachn-node block canbe read using one seek. Hence the worst case seeks comes downby a factor ofn/2.iv.Allowing redistribution among the nodes of the same block, doesnot require additional seeks, where as, in regular B+-tree werequire as many seeks as the number of leaf pages involvedin the redistribution. This makes redistribution for leaf blocksefficient with this scheme. Also the worst case occupancy comesback to nearly 50 percent. (Splitting of leaf nodes is preferredwhen the participating leaf nodes are nearly full. Hence nearly50 percent instead of exact 50 percent)
This is the end of the preview.
access the rest of the document.