Category: ASE: Data Storage

Overflow pages

Overflow pages are created in nonunique clustered indexes on APL tables when a new row is inserted which has the same key value as the last row on an already full data page. A new data page will be assigned to the respective page chain and linked in. The new row will be stored on this new, so-called overflow page.

The overflow page only stores rows with identical key values. Sometimes there can be numerous identical values, if data is inserted into a column with a nonunique index.

Example of an overflow page

Before the insert:

    insert table_name ('color') values ('blue')    

After the insert:

Characteristically, overflow pages are not directly referenced by the index pointers of clustered indexes Instead, the next page pointer is used to follow a chain of overflow pages. The next page pointer is followed until the search value cannot be matched anymore.