Addition of new records in a Binary tree structure always occurs as leaf nodes, which are further away from the root node making their access slower. If this new record is to be accessed frequently, then we cannot afford to spend much time in attainment of it but would require it to be positioned close to the root node. It would call for rebuilding or readjustment of the tree to attain the desired shape. But, this process of rebuilding the tree every time as the preferences for the records change is tedious and time consuming. There has to be some measure so that the tree adjusts itself automatically as the frequency of accessing the records changes. Such a self-adjusting tree is the Splay tree.
Splay trees are self-adjusting binary search trees in which every access for insertion or retrieval of any node, lifts that node all the way up to become the root, pushing the other nodes out of the way to make room for this new root of the modified tree. Hence, the frequently accessed nodes will frequently be lifted up and remain around the root position; whereas the most infrequently accessed nodes would move farther and farther away from the root.
This process of readjusting may at times create a highly imbalanced splay tree, wherein a single access may be extremely expensive. But over a long sequence of accesses, these expensive cases may be averaged out by the less expensive ones to produce excellent results over a long sequence of operations. The analytical tool utilized for this purpose is the Amortized algorithm analysis. This will be discussed fully in the following sections.