B* Trees for Tables with LONG Columns


The database system creates the following B* trees for LONG columns (LOBs):

?     One B* tree for the data records (primary tree), sorted by primary key

?     One B* tree for the short values in the LONG column

LONG values that are shorter than one page are also known as short LONG values or short column file. LONG values that are longer than one page are also known as long LONG values.

?     One additional B* tree for each long LONG value in the LONG column

For the values of the LONG column, the leaf pages of the primary tree contain either links to the B* tree for the short LONG values or links to the table ID of one of the B* trees for the long LONG values.

The following figure shows the B* trees for a base table with a LONG column, which contains two short LONG values and two long LONG values.

See also:

Logical Access Structures