I think WEKA software is a potential data mining tool which has a series of data mining techniques. This software is open-source software. so you can freely download it from internet.

Depending on how your input data is organized, some good options may be R, MATLAB or WEKA

i would suggest rapid miner 

Iam also suggests MATLAB

MATLAB would be the best.

MATLAB++

From solutions with a more user-friendly visual environment to those with more programming skills requirements; I would suggest:

- Orange: open source data mining package;

http://orange.biolab.si

- Weka: an open source stats and data mining library;

http://www.cs.waikato.ac.nz/ml/weka/

- RapidMiner: an open source statistical and data mining package;

https://rapidminer.com

- Scikit Leran

http://scikit-learn.org/stable/

- R

http://www.rdatamining.com

- Matlab or Octave

http://www.mathworks.com/

https://www.gnu.org/software/octave/

Also to help you effectively implement the algorithms I would pick one of these resources based on the chosen programming environment:

Python oriented:

- Programming Collective Intelligence http://shop.oreilly.com/product/9780596529321.do

Very popular among beginners with real-life examples (data)

Many Python examples

- Machine Learning an Algorithmic Perspective

http://www.amazon.com/Machine-Learning-Algorithmic-Perspective-Recognition/dp/1420067184

Mainly focused on algorithms

Not so much math and many Python examples

- Machine Learning in Action

http://www.amazon.com/Machine-Learning-Action-Peter-Harrington/dp/1617290181

Similar to the latter; algorithm hands-on

Many Python examples

Weka (platform) oriented:

- Data Mining: Practical Machine Learning Tools and Techniques

http://www.cs.waikato.ac.nz/ml/weka/book.html

Very good introduction on ML

It is a companion book for the Weka platform

Additionally:

- Tom Mitchell's book - Machine Learning (1997) - and online material

http://www.cs.cmu.edu/~tom/

- Christopher Bishop's - Pattern Recognition and Machine Learning (2007)

http://www.springer.com/gp/book/9780387310732

- Jason Brownlee's - Machine Learning Mastery web page.

http://machinelearningmastery.com

Good luck and have fun mining the web log data!

Matlab

if you need an open source software, i would Highly recommend  you R and  second choice will be WEKA.

Matlab and R

What is exact question? You want to know the algorithm or developing tool?

You can use WEKA as a learner. For web log data, You can also try R programming.

You may also try Tanagra, Orange in addition to the above list for pattern recognition.

MATLAB AND WEKA