Ayende @ Rahien

It's a girl

Lucene is beautiful

So, after I finished telling you how much I don’t like the lucene.net codebase, what is this post about?

Well, I don’t like the code, but then again, I generally don’t like to read low level code. The ideas behind Lucene are actually quite amazingly powerful in their simplicity.

At its core, Lucene is just a set of sorted dictionaries on disk (greatly simplified, I know). Everything else is build on top of that, and if you grok what is going on there, you would be quite amazed at the number of things that this has made possible.

Indexing in Lucene is done by a pipeline of documents and fields and analyzers, which all participate together to generate those dictionaries. Searching in lucene is done by traversing those dictionaries in various ways, and combining the results in interesting ways.

I am not going to go into details about how it works, you can read all about that here. The important thing is that once you have grasped the essential structure inside lucene, the rest are just details.

The concept and the way the implementation fell out are quite beautiful.

Comments

tobi
10/03/2012 10:26 AM by
tobi

It really is a NoSQL store. It uses sorted string tables on disk and merges them periodically, just like Cassandra and probably others.

Chris
10/03/2012 01:49 PM by
Chris

I love this sentence: "amazingly powerful in their simplicity". That might be the best thought I've read in a long time.

Bart Czernicki
10/04/2012 02:29 PM by
Bart Czernicki

Anyone that is a fan on Lucene.NET should buy that book (even though it is targeted for Java), because Lucene.NET (version 3.03 RC2) matches that version of the book exactly. Lucene 2.x != 3.x (big changes especially in the Analyzer classes)

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