Many users use ALTER FRAGMENT ATTACH and DETACH statements to add or remove a large amount of data in a very large table. ALTER FRAGMENT DETACH provides a way to delete a segment of the table data rapidly. Similarly, ALTER FRAGMENT ATTACH provides a way to load large amounts of data incrementally into an existing table by taking advantage of the fragmentation technology. However, the ALTER FRAGMENT ATTACH and DETACH statements can take a long time to execute when the database server rebuilds indexes on the surviving table.
The database server provides performance optimizations for the ALTER FRAGMENT ATTACH and DETACH statements that cause the database server to reuse the indexes on the surviving tables. Therefore, the database server can eliminate the index build during the attach or detach operation, which: