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Distributed Models Over Distributed Data with MLflow
Does more data always improve ML models? Is it better to use distributed ML instead of single node ML?
In this talk I will show that while more data often improves DL models in high variance problem spaces (with semi or unstructured data) such as NLP, image, video more data does not significantly improve high bias problem spaces where traditional ML is more appropriate. Additionally, even in the deep learning domain, single node models can still outperform distributed models via transfer learning.
Data scientists have pain points running many models in parallel automating the experimental set up. Getting others (especially analysts) within an organization to use their models Databricks solves these problems using pandas udfs, ml runtime and MLflow.
1 .Distributed Models Over Distributed Data with MLflow, Pyspark, and Pandas Thunder Shiviah email@example.com Senior Solutions Architect, Databricks SAIS EUROPE - 2019
2 .Abstract ● More data often improves DL models in high variance problem spaces (with semi or unstructured data) such as NLP, image, video but does not significantly improve high bias problem spaces where traditional ML is more appropriate. ● That said, in the limits of more data, there still not a reason to go distributed if you can instead use transfer learning. ● Data scientists have pain points ○ running many models in parallel ○ automating the experimental set up ○ Getting others (especially analysts) within an organization to use their models ● Databricks solves these problems using pandas udfs, ml runtime and mlflow.
3 .Why do single node data science?
4 .Is more data always better? The Unreasonable Effectiveness of Data, Alon Halevy, Peter Norvig, and Fernando Pereira, Google 2009
5 .Banko and Brill, 2001
6 .Team A came up with a very sophisticated algorithm using the Netflix data. Team B used a very simple algorithm, but they added in additional data beyond the Netflix set: information about movie genres from the Internet Movie Database (IMDB). Guess which team did better? Team B got much better results, close to the best results on the Netflix leaderboard! I'm really happy for them, and they're going to tune their algorithm and take a crack at the grand prize. But the bigger point is, adding more, independent data usually beats out designing ever-better algorithms to analyze an existing data set. I'm often surprised that many people in the business, and even in academia, don't realize this. - "More data usually beats better algorithms", Anand Rajaraman
7 .Okay, case closed. Right?
8 .Not so fast!
9 .● First Norvig, Banko & Brill were focused on NLP specifically, not general ML. ● Second, Norvig et al were not saying that ML models trained on more data are better than ML models trained on less data. Norvig was comparing ML (statistical learning) to hand coded language rules in NLP: “...a deep approach that relies on hand-coded grammars and ontologies, represented as complex networks of relations;” (Norvig, 2009) ● In his 2010 UBC Department of Computer Science's Distinguished Lecture Series talk, Norvig mentions that regarding NLP, google is quickly hitting their limits with simple models and is needing to focus on more complex models (deep learning). ● Re: the Netflix data set: The winning team actually then commented and said Our experience with the Netflix data is different. IMDB data and the likes gives more information only about the movies, not about the users ... The test set is dominated by heavily rated movies (but by sparsely rating users), thus we don't really need this extra information about the movies. Our experiments clearly show that once you have strong CF models, such extra data is redundant and cannot improve accuracy on the Netflix dataset.
10 .Netflix algorithm in production Netflix recommendations: beyond the 5 stars, Xavier Amatriain (Netflix)
11 .Oh, and what about the size of those data sets? ● 1 billion word corpus = ~2GB ● Netflix prize data = 700Mb compressed ○ 1.5 GB uncompressed (source)
12 .So where does that leave us?
13 .Bias vs Variance
15 .Andrew Ng, AI is the New Electricity
16 .Conclusion: more data makes sense for high variance (semi-structured or unstructured) problem domains like text and images. Sampling makes sense for high bias domains such as structured problem domains.
17 .Should we always use more data with deep learning?
18 .No! Transfer learning on smaller data often beats training nets from scratch on larger data-sets. Open AI pointed out that while the amount of compute has been a key component of AI progress, “Massive compute is certainly not a requirement to produce important results.” (source)
19 .In a benchmark run by our very own Matei Zaharia at Stanford, Fast.ai was able to win both fastest and cheapest image classification: Imagenet competition, our results were: ● Fastest on publicly available infrastructure, fastest on GPUs, and fastest on a single machine (and faster than Intel’s entry that used a cluster of 128 machines!) ● Lowest actual cost (although DAWNBench’s official results didn’t use our actual cost, as discussed below).Overall, our findings were: ● Algorithmic creativity is more important than bare-metal performance (source)
20 .Transfer learning models with a small number of training examples can achieve better performance than models trained from scratch on 100x the data Introducing state of the art text classification with universal language models, Jeremy Howard and Sebastian Ruder
21 .Take-away: Even in the case of deep learning, if an established model exists, it’s better to use transfer learning on small data then train from scratch on larger data
22 .So where does databricks fit into this story?
23 .Training models (including hyperparameter search and cross validation) is embarrassingly parallel
24 .Shift from distributed data to distributed models Introducing Pandas UDF for PySpark: How to run your native Python code with PySpark, fast.
25 .Data Scientists spend lots of time setting up their environment
26 .Rule of frequency: automate the things you do the most Source: xkcd
27 .Maybe... Source: xkcd
28 .ML runtime
29 .Data Scientists have a difficult time tracking models