What's the best way to implement web service for ajax autocomplete
I would use the first option. 'KISS' - (Keep It Simple Stupid).
For small amounts of data there shouldn't be much latency. We run the same kind of thing for a name search and results appear pretty quickly on a few thousand rows.
Hope that helps,
Josh
I'm implementing a "Google Suggest" like autocomplete feature for tag searching using jQuery's autocomplete. 
I need to provide a web service to jQuery giving it a list of suggestions based on what the user has typed. I see 2 ways of implementing the web service:
1) just store all the tags in a database and search the DB using user input as prefix. This is simple, but I'm concerned about latency.
2) Use an in-process trie to store all the tags and search it for matching results. As everything will be in-process, I expect this to have much lower latency. But there are several difficulties:
-What's a good way to initialize the trie on process start up? Presumable I'll store the tag data in a DB and retrieve them and turn them into a trie when I frist start up the process. But I'm not sure how. I'm using Python/Django. 
-When a new tag is created by a user, I need to insert the new tag into the trie. But let's say I have 5 Django processes and hence 5 tries, how do I tell the other 4 tries that they need to insert a new tag too?
-How to make sure the trie is threadsafe as my Django processes will be threaded (I'm using mod_wsgi). Or do I not have to worry about threadsafty because of Python's GIL?
-Any way I can store the tag's frequency of use within the trie as well? How do I tell when does the tag's string end and when does the frequency start - eg. if I store apple213 into the trie, is it "apple" with frequency 213 or is it "apple2" with frequency 13??
Any help on the issues above or any suggestions on a different approach would be really appreciated.