First section: This section contains an initial segment of the key fields of a table row. This section is called the separator. SAP DB uses only this part of the
primary key, which is required to distinguish the subsequent entries, thereby minimizing the storage space used in these pages.
The first separator in the leftmost page of each level (including the root level) contains only the pointer to the leftmost page of the next level down.
The average length of the separators depends on the structure and the selectivity of the primary key. If a very large number of key fields have to be evaluated to enable the entries (records) to be distinguished from each other, this results in longer separators.
Second section: This section contains the logical address of a page at a lower index level or at the leaf level. The number of entries in this section depends on the length of the separators.