Very nice introduction of Bill Graham (@billgraham) into Big Data and Hadoop.

UC Berkeley School of Information has a great course, where UC Berkeley professors and Twitter engineers are lectureing on the most cutting-edge algorithms and software tools for data analytics as applied to Twitter microblog data. Topics include applied natural language processing algorithms such as sentiment analysis, large scale anomaly detection, real-time search, information diffusion and outbreak detection, trend detection in social streams, recommendation algorithms, and advanced frameworks for distributed computing.
Bill Graham (@billgraham), who is active in the Hadoop community and a Pig contributor, gave a very clear and detailed intro to Hadoop and outlined how it is used at Twitter. His slides can be found here.

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UC Berkeley Course Lectures: Analyzing Big Data with Twitter