What triggers an index fragmentation?
Index fragmentation usually occurs when data is repeatedly deleted from the index and reinserted at a different location. In particular, this happens when a field is indexed whose values increase with time. If older entries are deleted, it is always from the left side of the index while new entries are always inserted on the right side of the index. As a result, the index tree is more or less empty on the left side, but keeps growing on the right side.
