Deep Learning with DL4J on Apache Spark

DeepLearning4J (DL4J) is a powerful Open Source distributed framework that brings Deep Learning to the JVM (it can serve as a DIY tool for Java, Scala, Clojure and Kotlin programmers). It can be used on distributed GPUs and CPUs. It is integrated with Hadoop and Apache Spark. ND4J is a Open Source, distributed and GPU-enabled library that brings the intuitive scientific computing tools of the Python community to the JVM. Training neural network models using DL4J, ND4J and Spark is a powerful combination, but it presents some unexpected issues that can compromise performance and nullify the benefits of well written code and good model design. In this talk I will walk through some of those problems and will present some best practices to prevent them, coming from lessons learned when putting things in production.

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1.WIFI SSID:Spark+AISummit | Password: UnifiedDataAnalytics

2.Deep Learning with DL4J on Apache Spark: Yeah it's Cool, but are You Doing it the Right Way? Guglielmo Iozzia, MSD #UnifiedDataAnalytics #SparkAISummit

3.About Me Currently at Previously at Author at Packt Publishing Got some awards lately Champion I love cooking 3 #UnifiedDataAnalytics #SparkAISummit #GuglielmoIozzia

4.MSD in ireland + 50 years Approx. 2,000 employees 2017 + 300 jobs & €280m investment MSD Biotech, Dublin, coming in 2021 $2.5 billion investment to date €6.1 billion turnover in 2017 Approx 50% MSD’s top 20 products manufactured here Export to + 60 countries #UnifiedDataAnalytics #SparkAISummit 4

5.The Dublin Tech Hub #UnifiedDataAnalytics #SparkAISummit 5

6.Deep Learning It is a subset of machine learning where artificial neural networks, algorithms inspired by the human brain, learn from large amounts of data. 6 #UnifiedDataAnalytics #SparkAISummit

7.Deep Learning http://www.asimovinstitute.org/wp-content/uploads/2019/04/NeuralNetworkZoo20042019.png 7 #UnifiedDataAnalytics #SparkAISummit

8.Deep Learning 8 #UnifiedDataAnalytics #SparkAISummit

9.Some practical applications of Deep Learning • Computer vision • Text generation • NLP and NLU • Autonomous cars • Robotics • Gaming • Quantitative finance • Manufacturing #UnifiedDataAnalytics #SparkAISummit 9

10.Challenges of training MNNs in Spark • Different execution models between Spark and the DL frameworks • GPU configuration and management • Performance • Accuracy #UnifiedDataAnalytics #SparkAISummit 10

11. DeepLearning4J It is integrated with Hadoop and Apache Spark. It is an Open Source, distributed, Deep Learning framework written for JVM languages. It can be used on distributed GPUs and CPUs. #UnifiedDataAnalytics #SparkAISummit 11

12.DL4J modules • DataVec • Arbiter • NN • Datasets • RL4J • DL4J-Spark • Model Import • ND4J #UnifiedDataAnalytics #SparkAISummit 12

13.DL4J Code Example Training and Evaluation Network Configuration #UnifiedDataAnalytics #SparkAISummit 13

14.ND4J It is an Open Source linear algebra and matrix manipulation library which supports n-dimensional arrays and it is integrated with Apache Hadoop and Spark. 14 #UnifiedDataAnalytics #SparkAISummit

15.ND4J Code Example #UnifiedDataAnalytics #SparkAISummit 15

16.Why Distributed MNN Training with DL4J and Apache Spark? Why this is a powerful combination? #UnifiedDataAnalytics #SparkAISummit 16

17.DL4J + Apache Spark • DL4J provides high level API to design, configure, train and evaluate MNNs. • Spark performances are excellent in particular for ETL/streaming, but in terms of computation, in a MNN training context, some data transformation/aggregation need to be done using a low-level language. • DL4J uses ND4J, which is a C++ library that provides high level Scala API to developers. #UnifiedDataAnalytics #SparkAISummit 17

18.DL4J + Apache Spark Model Parallelization Data Parallelization #UnifiedDataAnalytics #SparkAISummit 18

19.How Training Happens in Spark with DL4J? Asynchronous SDG Parameter Averaging (DL4J 1.0.0-beta+) (DL4J 1.0.0-alpha) #UnifiedDataAnalytics #SparkAISummit 19

20.So: What could possibly go wrong? #UnifiedDataAnalytics #SparkAISummit 20

21.Memory Management And now, for something (a little bit) different. #UnifiedDataAnalytics #SparkAISummit 21

22.Memory Utilization at Training Time #UnifiedDataAnalytics #SparkAISummit 22

23.Memory Management in DL4J Memory allocations can be managed using two different approaches: • JVM GC and WeakReference tracking • MemoryWorkspaces The idea behind both is the same: once a NDArray is no longer required, the off-heap memory associated with it should be released so that it can be reused. #UnifiedDataAnalytics #SparkAISummit 23

24.Memory Management in DL4J The difference between the two approaches is: • JVM GC: when a INDArray is collected by the garbage collector, its off-heap memory is deallocated, with the assumption that it is not used elsewhere. • MemoryWorkspaces: when a INDArray leaves the workspace scope, its off-heap memory may be reused, without deallocation and reallocation. Better performance for training and inference. #UnifiedDataAnalytics #SparkAISummit 24

25.Memory Management in DL4J Please remember that, when a training process uses workspaces, in order to get the most from this approach, periodic GC calls need to be disabled: Nd4j.getMemoryManager.togglePeriodicGc(false) or their frequency needs to be reduced: val gcInterval = 10000 // In milliseconds Nd4j.getMemoryManager.setAutoGcWindow(gcInterval) #UnifiedDataAnalytics #SparkAISummit 25

26.The DL4J training UI #UnifiedDataAnalytics #SparkAISummit 26

27.Root Cause and Potential Solutions Dependencies conflict between the DL4J-UI library and Apache Spark when running in the same JVM. Two alternatives are available: • Collect and save the relevant training stats at runtime, and then visualize them offline later. • Execute the UI and use its remote functionality into separate JVMs (servers). Metrics are uploaded from the Spark master to the UI server. #UnifiedDataAnalytics #SparkAISummit 27

28.Serialization & ND4J Data Serialization is the process of converting the in-memory objects to another format that can be used to store or send them over the network. Two options available in Spark: • Java (default) • Kryo #UnifiedDataAnalytics #SparkAISummit 28

29.Do You Opt for Kryo? Kryo doesn’t work well with off-heap data structures. #UnifiedDataAnalytics #SparkAISummit 29