The indexing function is performed by the indexer and the sorter.
The indexerperforms a number of functions.
This scheme requires slightly more storagebecause of duplicated docIDs but the difference is very small for a reasonablenumber of buckets and saves considerable time and coding complexity inthe final indexing phase done by the sorter.
The indexer performs another important function.
Anyone who has used a searchengine recently, can readily testify that the completeness of the indexis not the only factor in the quality of search results.