Multi-prefix query optimizations

An information retrieval system including a non-transitory computer-accessible storage medium for conducting, and caching results of user queries of a database of content items across a plurality of channels, each channel representing a category of content items within the database, the system comprising:

• (a) a search module that retrieves from an index, for each character of a user query term entered by a user into a mobile device, a list of records containing at least one word having characters matching the characters of the user query term;
• (b) a multi-tier search module that limits a first user query to a first tier of content that contains names of channels in the database, and, upon receiving an indication of the user's selection of the name of a first channel, displays on the mobile device a dynamic search box which limits a second user query to a second tier of content that contains items within the category represented by the name of the first channel;
• and
• (c) a result delivery module that:
• (i) generates a result list by intersecting the lists of records retrieved from the index,
• (ii) organizes the result list based on at least one positional ranking factor,
• (iii) computes the value of a query function to determine whether to cache the result list, wherein the value of the query function is dependent upon a plurality of factors, including the total number of characters in the user query and the processing time required to retrieve and intersect the lists of records from the index to generate the result list, and
• (iiv) conditionally caches the result list in storage, based upon a comparison of the value of the query function to a predefined threshold,
• (d) whereby the processing time for a subsequent user query is decreased by retrieving the cached result list from storage.