BLZ: A chunked, compressed, data container (for memory and disk)

BLZ is a chunked container for numerical data. Chunking allows for efficient enlarging/shrinking of data container. In addition, it can also be compressed for reducing memory/disk needs. The compression process is carried out internally by Blosc, a high-performance compressor that is optimized for binary data.

BLZ uses numexpr internally so as to accelerate many vector and query operations. numexpr can use optimize the memory usage and use several cores for doing the computations, so it is blazing fast. Moreover, with the introduction of a barray/btable disk-based container (in version 0.5), it can be used for seamlessly performing out-of-core computations.

Rational

By using compression, you can deal with more data using the same amount of memory. In case you wonder: which is the price to pay in terms of performance? you should know that nowadays memory access is the most common bottleneck in many computational scenarios, and CPUs spend most of its time waiting for data, and having data compressed in memory can reduce the stress of the memory subsystem.

In other words, the ultimate goal for BLZ is not only reducing the memory needs of large arrays, but also making operations to go faster than using a traditional ndarray object from NumPy. That is already the case for some special cases now, but will happen more generally in a short future, when BLZ will be able to take advantage of newer CPUs integrating more cores and wider vector units.

Requisites

• Python >= 2.6
• NumPy >= 1.7
• Cython >= 0.19
• numexpr >= 2.2 (optional, if not present, plain NumPy will be used)
• Blosc >= 1.3.0 (optional, the internal Blosc will be used by default)
• unittest2 (only in the case you are running Python 2.6)

Building

Assuming that you have the requisites and a C compiler installed, do:

$ python setup.py build_ext --inplace

In case you have Blosc installed as an external library (and disregard the included Blosc sources) you can link with it in a couple of ways.

Using an environment variable:

$ BLOSC_DIR=/usr/local     (or "set BLOSC_DIR=\blosc" on Win)
$ export BLOSC_DIR         (not needed on Win)
$ python setup.py build_ext --inplace

Using a flag:

$ python setup.py build_ext --inplace --blosc=/usr/local

Testing

After compiling, you can quickly check that the package is sane by running:

$ PYTHONPATH=. (or "set PYTHONPATH=." on Windows) $ export PYTHONPATH (not needed on Windows) $ python -c"import blz; blz.test()" # add heavy=True if desired

Installing

Install it as a typical Python package:

$ python setup.py install

Documentation

Please refer to the docs/ directory.

Also, you may want to look at the bench/ directory for some examples of use.

** To be completed **

Resources

Visit the main BLZ site repository at: http://github.com/ContinuumIO/blz

Home of Blosc compressor: http://www.blosc.org

Read the online docs at: http://blz.pydata.org/blz-manual/index.html

User's mail list: blaze-dev@continuum.io

License

Please see BLZ.txt in LICENSES/ directory.

Share your experience

Let us know of any bugs, suggestions, gripes, kudos, etc. you may have.

Francesc Alted Continuum Analytics Inc.