How to implement the search functionality on a website?

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I want to implement search functionality for a website (assume it is similar to SO). I don't want to use Google search of stuff like that.

My question is:

How do I implement this?

There are two methods I am aware of:

  1. Search all the databases in the application when the user gives his query.
  2. Index all the data I have and store it somewhere else and query from there (like what Google does).

Can anyone tell me which way to go? What are the pros and cons?

Better, are there any better ways to do this?


Use lucene,
http://lucene.apache.org/java/docs/

Apache Lucene is a high-performance, full-featured text search engine library written entirely in Java. It is a technology suitable for nearly any application that requires full-text search, especially cross-platform.

It is available in java and .net. It is also in available in php in the form of a zend framework module.

Lucene does what you wanted(indexing of the searched items), you have to keep track of a lucene index but it is much better than doing a database search in terms of performance. BTW, SO search is powered by lucene. :D