number of items on the reduced pagebecauseif nthe primary characteristic of -trees would be violated some additional action has to be takenthis underflow condition is indicated by the boolean variable parameter the only recourse is to borrow or annect an item from one of the neighboring pagessay from since this involves fetching page into main store - relatively costly operation -one is tempted to make the best of this undesirable situation and to annect more than single item at once the usual strategy is to distribute the items on pages and evenly on both pages this is called page balancing of courseit may happen that there is no item left to be annected since has already reached its minimal size in this case the total number of items on pages and is - we may merge the two pages into oneadding the middle item from the ancestor page of and qand then entirely dispose of page this is exactly the inverse process of page splitting the process may be visualized by considering the deletion of key in fig once againthe removal of the middle key in the ancestor page may cause its size to drop below the permissible limit nthereby requiring that further special action (either balancing or mergingbe undertaken at the next level in the extreme case page merging may propagate all the way up to the root if the root is reduced to size it is itself deletedthereby causing reduction in the height of the btree this isin factthe only way that -tree may shrink in height figure shows the gradual decay of the -tree of fig upon the sequential deletion of the keys the semicolons again mark the places where the snapshots are takennamely where pages are being eliminated the similarity of its structure to that of balanced tree deletion is particularly noteworthy de fig decay of -tree of order type page pointer to pagerecentry record (adens _btrees *