I have a few questions related with the use of Apache Spark for real-time analytics using Java. When the Spark application is submitted, the data that are stored in Cassandra database are loaded and processed via a machine learning algorithm (Support Vector Machine). Throughout Spark's streaming extension when new data arrive, they are persisted in the database, the existing dataset is re-trained and the SVM algorithm is executed. The output of this process is also stored back in the database.
- Apache Spark's MLLib provides implementation of linear support vector machine. In case that I would like a non-linear SVM implementation, should I implement my own algorithm or may I use existing libraries such as libsvm or jkernelmachines? These implementations are not based on Spark's RDDs, is there a way to do this without implementing the algorithm from scratch using RDD collections? If not, that would be a huge effort if I would like to test several algorithms.
- Is MLLib providing out of the box utilities for data scaling before executing the SVM algorithm? http://www.csie.ntu.edu.tw/~cjlin/papers/guide/guide.pdf as defined in section 2.2
- While new dataset is streamed, do I need to re-train the hole dataset? Is there any way that I could just add the new data to the already trained data?
To answer your questions piecewise,
- Spark provides the MLUtils class that allows you to load data from the LIBSVM format into RDDs - so just the data load portion won't stop you from utilizing that library. You could also implement your own algorithms if you know what you're doing, although my recommendation would be to take an existing one and tweak the objective function and see how it runs. Spark basically provides you the functionality of a distributed Stochastic Gradient Descent process - you can do anything with it.
- Not that I know of. Hopefully someone else knows the answer.
- What do you mean by re-training when the whole data is streamed?
From the docs,
.. except fitting occurs on each batch of data, so that the model continually updates to reflect the data from the stream.
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