10. A disk memory storing instructions that when executed perform operations for dynamic updating of an index of a search engine, comprising: storing the index on a mass storage device of a search engine that is implemented on one or more servers, the index being an inverted index, the index comprising a dictionary that maps words to word identifiers, a posting file, and a database log that stores changes to the dictionary as the changes occur, the posting file having posting lists for each keyword of the index; generating a position list for a keyword, wherein the position list gives all locations of the keyword in the documents; inserting a record in the database log in response to each change made to the dictionary, the record including the keyword, the position list and a reference to a previous record of the same keyword in the database log, said previous entry having a reference stored in the mass storage device as the last added entry of all recently added keywords; retrieving a dictionary entry from the dictionary that corresponds to a keyword, using data indicated by the dictionary entry to read a given position list and a given delta list from the posting file, the given position list indicating positions of the given keyword, the given delta list containing changes to the given occurrence list, merging into a single position list the given position list, updates from the given delta list and given entries in the database log, the given entries in the database log indicating modifications to the given position list; and using the single position list for further processing of a search query.
10. A disk memory storing instructions that when executed perform operations for dynamic updating of an index of a search engine, comprising: storing the index on a mass storage device of a search engine that is implemented on one or more servers, the index being an inverted index, the index comprising a dictionary that maps words to word identifiers, a posting file, and a database log that stores changes to the dictionary as the changes occur, the posting file having posting lists for each keyword of the index; generating a position list for a keyword, wherein the position list gives all locations of the keyword in the documents; inserting a record in the database log in response to each change made to the dictionary, the record including the keyword, the position list and a reference to a previous record of the same keyword in the database log, said previous entry having a reference stored in the mass storage device as the last added entry of all recently added keywords; retrieving a dictionary entry from the dictionary that corresponds to a keyword, using data indicated by the dictionary entry to read a given position list and a given delta list from the posting file, the given position list indicating positions of the given keyword, the given delta list containing changes to the given occurrence list, merging into a single position list the given position list, updates from the given delta list and given entries in the database log, the given entries in the database log indicating modifications to the given position list; and using the single position list for further processing of a search query. 11. The disk memory according to claim 10 , further comprising: grouping updates of the database log together at specified intervals moving the grouped updates to the posting file; and storing each keyword respectively in an occurrence list in the form of occurrences of the keyword older than a determined update generation and in a delta list in the form of a set of smaller updates more recent than the same update generation, such that the dictionary contains one entry for each keyword in the posting file and a reference to the occurrence list and the delta list.