It is possible to specify B-tree leaf page fill factors at modify time. This is the percentage of the leaf page that is used during the modify procedure. The remaining portion of the page is available for use later when new rows are added to the table.

The purpose of the fill factor is to leave extra room on the leaf pages to do inserts without causing leaf page splits. This is useful if you modify a table to B-tree and plan to add rows to it later.

In VDBA, you control these values using the Leaffill options in the Structure of Table dialog.

The Leaffill option specifies the percentage of each leaf page to be filled at the time the table is modified to B-tree or cB-tree. The Leaffill default is 70, which means that 70% of the leaf page is filled at modify time and 30% remains empty for future use.

For example, assume that the key-tid pair requires 400 bytes of storage. This means that five key-tid pairs fit on a single 2 KB B-tree leaf page. However, if the leaf page fill factor is specified at 60%, only three key-tid pairs are allocated on each B-tree leaf page at modify time. If subsequent updates to the table cause two new rows on this leaf page, they are placed in the empty space on the leaf page. The key-tid pairs are reordered on the leaf page from min to max. If more than two new rows need to be added to this leaf page, there is not enough space and the leaf page has to split.