There are several reasons to consider rebuilding your database. You might rebuild your database if you want to do any of the following:
Upgrade your database file format Some new features are made available by applying the Upgrade utility, but others require a database file format upgrade, which is performed by unloading and reloading the database. The New Features documentation states whether an unload and reload is required to obtain a particular feature.New versions of the SQL Anywhere database server can be used without upgrading your database. If you want to use features of the new version that require access to new system tables or database options, you must use the Upgrade utility to upgrade your database. The Upgrade utility does not unload or reload any data. If you want to use the new version of SQL Anywhere that relies on changes in the database file format, you must unload and reload your database. You should back up your database before rebuilding the database.
If you are upgrading from version 9 or earlier to version 10, you must rebuild the database file. If you are upgrading from version 10.0.0, you can use the Upgrade utility or rebuild your database.
Reclaim disk space Databases do not shrink if you delete data. Instead, any empty pages are simply marked as free so they can be used again. They are not removed from the database unless you rebuild it. Rebuilding a database can reclaim disk space if you have deleted a large amount of data from your database and do not anticipate adding more.
Improve database performance Rebuilding databases can improve performance. Since the database can be unloaded and reloaded in order by primary keys, access to related information can be faster as related rows may appear on the same or adjacent pages.
If you detect that performance is poor because a table is highly fragmented, you can reorganize the table. See REORGANIZE TABLE statement.