ArcCatalog modifies spatial indexes by deleting them, then re-adding them in a two-step process. Versioned feature classes can only have their indexes modified by altering them.
Once there is data in a geodatabase table or feature class, to make queries faster, it may be necessary to create attribute indexes. Spatial indexes increase the selection speed of graphical queries on spatial features. An attribute index is an alternate path used by the DBMS to retrieve a record from a table. It is much faster to first look up the index and then go to the appropriate record than to start at the first record and search through the entire table.
Attribute indexes can be created for single or multiple fields on the feature class and table property pages. Once an index is added, it can be deleted and re-add it at any point in the lifetime of the feature class or table.
The same property page can be used to delete a spatial index and a spatial index can be added to the ArcSDE feature class.
The spatial index can be modified for an ArcSDE feature class by deleting the index and recreating it. The features stored in an ArcSDE feature class cannot be accessed if it does not have a spatial index.