Hi Digy,
Unfortunately I don't exactly have any performance tests with the
raw/trunk Lucene.
Like I said, I'm using my own filters which depend on being able to go
through the BitArray fast, a search for a term in my index can return
even as much as 500,000 results. I get the BitArray from Lucene and then
go through all 500,000 set bits so I can find out which document id it
is, and then look up the coordinates of that document id and compare
with my boundary box.
This requires a fast GetNextSetBit/Get implementation which is only
possible through unsafe code.
I can safely say however, that with the default .NET BitArray class, and
default GetNextSetBit implementation, the search was completely
unusable, sporting times of several seconds.
So, with the trunk Lucene, using the default filters, the net gain is
probably in the 10% range at most, I've seen that not many bit pushing
is involved with regular searches, bit maps being retrieved directly
from the Lucene index. But the moment you want to do something more
complicated with filters, then the limitations of the .NET BitArray
class become apparent.
Right now I can do very complex searches such as: "term AND field:(1111
OR 2222 OR 3333 OR 4444 OR 5555)" in under 200 ms for the initial
search, and then about 50 ms for any subsequent searches. I also
implemented some WeakReference based caching.
Regarding licensing issues, I would suggest you code a BitArray class
from scratch and name it something else, it's not really hard to make a
bit manipulation class, and that would solve licensing issues. I only
attached mine for reference (and mine is not fully optimized anyway).
Regards,
Andrei
Digy wrote:
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
