When the index is created, the user is required to supply the name of
the index, the length and AttrType of the key and the number of
initial buckets. (Its default value is 1.) Then a new page is created
(by Buffer Manager) as the RootPage and its PageId is given to db
to set the file entry for the index. Then HeaderPage, DirPages and
initial buckets are created and initialized.
When the index is opened, the user is required to supply the name of
the index. Then the name is passed to db to get the PageId of
RootPage. The RootPage is read into the buffer pool. The page
number of HeaderPage is on the RootPage and from header page we can access
all the pages in the index.