Search notes:
Oracle: Bitmap Indexes
A
bitmap index stores
rowids associated key values as a bitmap. A bitmap is maintained for each distinct key.
Unlike with other indexes, bitmap indexes also create index entries for rows where all indexed column values are
null.
When adding compressed data to a table with bitmap indexes, these indexes must be marked unusable.
Bitmap indexes that are marked invalid cannot be rebuilt. Such indexes must be dropped and recreated instead.
A bitmap index also cannot be created as reversed index.