Hi Andrei, Thanks for sharing your experience, but I have two questions regarding to your code. - Do you have some performance tests using BitArray & BitArrayEx? What is the gain? - I am not good about licensing issues. Do you think that it can be used in an apache project(since I see an MS copyright)?
DIGY. -----Original Message----- From: Andrei Alecu [mailto:and...@tachyon-labs.com] Sent: Saturday, December 13, 2008 3:05 PM To: lucene-net-dev@incubator.apache.org Subject: Performance improvements - BitArrays Hello all, This is my first message here. I've been using Lucene.NET for a while for a pretty big local search engine website and thought I'd share some of the performance improvements I came across. I made lots of changes to the Lucene code base in the process, and had to write my own geographical based filters and sort classes. I got it to a point where it can do a search through 17,000,000 records in under 200 ms, all this while also filtering results so they are within specified coordinates (each listing having its own coordinates), and also sorting results by distance to a certain point of origin - all on one machine. And I'm pretty sure it can be made even faster. I'd like to share one of the easy and pretty noticeable performance improvements I did. Lucene.NET, in its current implementation, makes heavy use of the .NET BitArray class. This class is not really performance optimized at all (you can look through the sources from Microsoft). The problem is that Microsoft sealed the BitArray class so you can't derive from it, so I got the sources from Microsoft and then heavily optimized them for performance using pointers (unsafe code), and some improved algorithms for finding the Next Set Bit (which I use extensively in my own Geo-filters). Also, if you can remove some of the valid argument checks from the BitArray class, then that's all the better for performance as well, because methods that throw explicit errors are not inlined by the .NET JIT. The other big improvement I did was to keep a renewable pool of BitArray classes in memory in order to minimize garbage collection. What this means is, whenever I need a new BitArray, instead of creating a completely new instance that the GC has to manage, I get one from a pool of 'released' BitArrays. When I'm done with a BitArray, instead of letting it go to the GC, I just put it back in the pool so it can be reused. This reduced GCs to a minimum in my application, and the memory footprint of my application is also much more stable. I realize however that this second improvement would break the Java code compatibility so it's just something more advanced users would want to do for themselves. I'm not sure if attaching files here works, but I'll attach the performance BitArray class I have. Thanks for all your hard work everyone! Kind regards, Andrei Alecu
