How to update the index quickly?

[何建云]

Hi,
I am using nutch for a search engine. I can not index webpages until the entire 
crawling process has ended. But i would like a quick update operation. The data 
crawled in front of several  can be added to the index even if the entire crawl 
process is not over yet.
1. Have any good idea?
2. If i do the indexing operation after every crawl depth, it will waste a lot 
of time. Beause the current solution is rebuilding the whole index. Is it 
possible to index incrementally?
thanks.