The FastPFOR C++ library : Fast integer compression

by Daniel Lemire, Leonid Boytsov, Owen Kaser, Maxime Caron, Louis Dionne

What is this?

A research library with integer compression schemes. It should be suitable for applications to d-gap compression and delta coding in general.

Reference and documentation

Please see:

Daniel Lemire and Leonid Boytsov, Decoding billions of integers per second through vectorization http://arxiv.org/abs/1209.2137

License

This code is licensed under Apache License, Version 2.0 (ASL2.0).

Requirements

This code requires a (recent as of 2012) compiler supporting C++11. This was a design decision. It builds under both clang++ 3.2 (LLVM 3.2) and GCC 4.7. The code was tested under Linux and MacOS.

Building with CMake

At the root of the project:

• Create a directory to contain the out-of-source build.

    mkdir build
    cd build
  

• Generate the files to actually perform the build. Many build systems are supported by CMake, so you may want to look at the documentation.

    cmake ..
  

• Given you generated Unix Makefiles (the default), you can now build the library.

    make
  

Building with make

You can specify which C++ compiler you are using with the YOURCXX variable.

e.g., under bash type

export YOURCXX=g++-4.7
make

Installing GCC 4.7 under Linux

Under a recent version of Ubuntu (12.10), you can install GCC 4.7 by typing:

sudo apt-get install gcc-4.7 g++-4.7

Installing GCC 4.7 under Mac

Mac Ports supports GCC 4.7. You can install it by typing:

sudo port install gcc47

Why C++11?

With minor changes, all schemes will compile fine under compilers that do not support C++11. And porting the code to C should not be a challenge.

What if I prefer Java?

Many schemes cannot be efficiently ported to Java. However some have been. Please see:

https://github.com/lemire/JavaFastPFOR

Testing

If you used CMake to generate the build files, the check target will run the unit tests. For example , if you generated Unix Makefiles

make check

will do it. If you used raw make, type the following:

make
./unit

Note that we are thorough in the unit tests so it can take several minutes to run through them all.

Simple benchmark

make codecs
./codecs --clusterdynamic
./codecs --uniformdynamic

Optional : Snappy

Typing "make allallall" will install some testing binaries that depend on Google Snappy. If you want to build these, you need to install Google snappy. You can do so on a recent ubuntu machine as:

sudo apt-get install libsnappy-dev

Processing data files

Typing make will generate an inmemorybenchmark executable that can process data files.

You can use it to process arrays on (sorted!) integers on disk using the following 32-bit format: 1 unsigned 32-bit integer indicating array length followed by the corresponding number of 32-bit integer. Repeat.

( It is assumed that the integers are sorted.)

Once you have such a binary file somefilename you can process it with our inmemorybenchmark:

./inmemorybenchmark --minlength 10000 somefilename

The "minlength" flag skips short arrays. (Warning: timings over short arrays are unreliable.)

Testing with the ClueWeb09 data set

Grab the data set from:

http://boytsov.info/datasets/clueweb09gap/

Using the provided software, uncompress it and run the "toflat" executable to create a "clueweb09.bin" file then run:

./inmemorybenchmark --minlength 10000 clueweb09.bin

Note: processing can take over an hour.

Testing with the Gov2 data set

You can test the library over d-gaps data from the TREC GOV2 data set that was made graciously available by Fabrizio Silvestri, Takeshi Yamamuro and Rossano Venturini.

Go to:

http://integerencoding.isti.cnr.it/?page_id=8

Download both the software and the gov.sort.tar file.

Untar the tar file:

tar xvf gov2.sort.tar

You may want to make the newly generated files non-writeable (I'm paranoid):

chmod -w gov2.sort.Delta gov2.sort.Delta.TOC

Build the software (you need the decoders executable) and

You need to run this command

./decoders 3 gov2.sort somefilename

where "3" is for delta.

Then you should be able to test with out inmemorybenchmark:

./inmemorybenchmark --minlength 10000 somefilename.DEC

Note: processing can take over an hour.

I used your code and I get segmentation faults

Our code is thoroughly tested.

One common issue is that people do not provide large enough buffers. Some schemes can have such small compression rates that the compressed data generated will be much larger than the input data.

Also, make sure that all provided buffers are 16-byte aligned or else, some SSE instructions may fail.

Is any of this code subject to patents?

I (D. Lemire) did not patent anything.

However, we implemented varint-G8UI which was patented by its authors.