A full documentation manual for the indexed search extension can be found in the extension "doc_indexed_search" in the TER.
See http://typo3.org/documentation/document-library/extension-manuals/doc_indexed_search/current/view/

This is a list of all tables which are used by this extension:

index_phash
- Page information

index_fulltext
- Fulltext data

index_rel
- Relations between index_phash and index_words

index_words
- baseword table

index_section
- section index (= first 3 levels of the rootline for this document)

index_grlist
- group list information
- indicates which gr_list has access to which phash