PyData Paris 2015 - Closing keynote Francesc Alted
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The document discusses trends in storing and analyzing large data sets using Python, highlighting the importance of optimizing data storage performance for existing and future computer architectures. It introduces bcolz as an efficient data container that utilizes chunked storage and supports better performance with modern hardware. Key considerations include interactivity, hardware trends, and the potential for using efficient libraries to enhance performance.
PyData Paris 2015 - Closing keynote Francesc Alted
- 1. New Trends In Storing And Analyzing Large Data Silos With Python Francesc Alted! Freelancer (ÜberResearch, University of Oslo) ! April 3rd, 2015
- 2. About ÜberResearch • Team’s 10+ years experience delivering solutions and services for funding and research institutions • Over 20 development partners, and clients globally, from smallest non-profits to large government agencies • Portfolio company of Digital Science (Macmillan Publishers), the younger sibling of the Nature Publishing Group http://www.uberresearch.com/
- 4. About Me • Physicist by training • Computer scientist by passion • Open Source enthusiast by philosophy • PyTables (2002 - 2011) • Blosc (2009 - now) • bcolz (2010 - now)
- 5. –Manuel Oltra, music composer “The art is in the execution of an idea. Not in the idea. There is not much left just from an idea.” “Real artists ship” –Seth Godin, writer Why Free/Libre Projects? • Nice way to realize yourself while helping others
- 7. Overview • The need for speed: fitting and analyzing as much data as possible with your existing resources • Recent trends in computer hardware • bcolz: an example of data container for large datasets following the principles of newer computer architectures
- 8. The Need For Speed
- 9. Don’t Forget Python’s Real Strengths • Interactivity • Data-oriented libraries (NumPy, Pandas, Scikit- Learn…) • Interactivity • Performance (thanks to Cython, SWIG, f2py…) • Interactivity (did I mentioned that already?)
- 10. The Need For Speed • But interactivity without performance in Big Data is a no go • Designing code for data storage performance depends very much on computer architecture • IMO, existing Python libraries need more effort in getting the most out of existing and future computer architectures
- 11. The Daily Python Working Scenario Quiz: which computer is best for interactivity?
- 12. Although Modern Servers/Laptops Can Be Very Complex Beasts We need to know them better so as to get the most out of them
- 13. Recent Trends In Computer Hardware “There's Plenty of Room at the Bottom” An Invitation to Enter a New Field of Physics —Talk by Richard Feynman at Caltech, 1959
- 14. Memory Access Time vs CPU Cycle Time The gap is wide and still opening!
- 15. Computer Architecture Evolution Up to end 80’s 90’s and 2000’s 2010’s Figure 1. Evolution of the hierarchical memory model. (a) The primordial (and simplest) model; (b) the most common current Mechanical disk Mechanical disk Mechanical disk Speed Capacity Solid state disk Main memory Level 3 cache Level 2 cache Level 1 cache Level 2 cache Level 1 cache Main memoryMain memory CPUCPU (a) (b) (c) Central processing unit (CPU)
- 16. Latency Numbers Every Programmer Should Know Latency Comparison Numbers -------------------------- L1 cache reference 0.5 ns Branch mispredict 5 ns L2 cache reference 7 ns 14x L1 cache Mutex lock/unlock 25 ns Main memory reference 100 ns 20x L2 cache, 200x L1 cache Read 4K randomly from memory 1,000 ns 0.001 ms Compress 1K bytes with Zippy 3,000 ns Send 1K bytes over 1 Gbps network 10,000 ns 0.01 ms Read 4K randomly from SSD* 150,000 ns 0.15 ms Read 1 MB sequentially from memory 250,000 ns 0.25 ms Round trip within same datacenter 500,000 ns 0.5 ms Read 1 MB sequentially from SSD* 1,000,000 ns 1 ms 4X memory Disk seek 10,000,000 ns 10 ms 20x datacenter roundtrip Read 1 MB sequentially from disk 20,000,000 ns 20 ms 80x memory, 20X SSD Send packet CA->Netherlands->CA 150,000,000 ns 150 ms Source: Jeff Dean and Peter Norvig (Google), with some additions https://gist.github.com/hellerbarde/2843375
- 17. tref ttrans CPU cache CPU cache Block in storage to transmit to CPU Reference Time vs Transmission Time tref ~= ttrans => optimizes memory access
- 18. Not All Storage Layers Are Created Equal Memory: tref: 100 ns / ttrans (1 KB): ~100 ns Solid State Disk: tref: 10 us / ttrans (4 KB): ~10 us Mechanical Disk: tref: 10 ms / ttrans (1 MB): ~10 ms This has profound implications on how you access storage! The slower the media, the larger the block that is worth to transmit
- 19. We Are In A Multicore Age • This requires special programming measures to leverage all its potential: threads, multiprocessing
- 20. SIMD: Single Instruction, Multiple Data More operations in the same CPU clock
- 21. The growing gap between DRAM and HDD is facilitating the introduction of new SDD devices Forthcoming Trends (I)
- 23. Bcolz: An Example Of Data Containers Applying The Principles Of New Hardware
- 24. What is bcolz? • bcolz provides data containers that can be used in a similar way than the ones in NumPy, Pandas • The main difference is that data storage is chunked, not contiguous! • Two flavors: • carray: homogenous, n-dim data types • ctable: heterogeneous types, columnar
- 25. Contiguous vs Chunked NumPy container Contiguous memory carray container chunk 1 chunk 2 Discontiguous memory chunk N ...
- 26. Why Chunking? • Chunking means more difficulty handling data, so why bother? • Efficient enlarging and shrinking • Compression is possible • Chunk size can be adapted to the storage layer (memory, SSD, mechanical disk)
- 27. Why Columnar? • Because it adapts better to newer computer architectures
- 28. String … String Int32 Float64 Int16 String … String Int32 Float64 Int16 String … String Int32 Float64 Int16 String … String Int32 Float64 Int16 Interesting column Interesting Data: N * 4 bytes (Int32) Actual Data Read: N * 64 bytes (cache line) }N rows In-Memory Row-Wise Table (Structured NumPy array)
- 29. String … String Int32 Float64 Int16 String … String Int32 Float64 Int16 String … String Int32 Float64 Int16 String … String Int32 Float64 Int16 Interesting column Interesting Data: N * 4 bytes (Int32) Actual Data Read: N * 4 bytes (Int32) In-Memory Column-Wise Table (bcolz ctable) }N rows Less memory travels to CPU!
- 30. Copy! Array to be enlarged Final array object Data to append New memory allocation • Both memory areas have to exist simultaneously Appending Data in NumPy
- 31. Appending Data in bcolz final carray object chunk 1 chunk 2 new chunk(s) carray to be enlarged chunk 1 chunk 2 data to append X compression Only compression on new data is required! Blosc Less memory travels to CPU!
- 32. Why Compression (I)? Compressed Dataset Original Dataset More data can be packed using the same storage
- 33. Why Compression (II)? Less data needs to be transmitted to the CPU Disk or Memory Bus Decompression Disk or Memory (RAM) CPU Cache Original Dataset Compressed Dataset Transmission + decompression faster than direct transfer?
- 34. Blosc: Compressing Faster Than memcpy()
- 35. How Blosc Works Multithreading & SIMD at work! Figure attr: Valentin Haenel
- 37. –Release Notes for OpenVDB 3.0, maintained by DreamWorks Animation “Blosc compresses almost as well as ZLIB, but it is much faster” Blosc In OpenVDB And Houdini
- 38. Some Projects Using bcolz • Visualfabriq’s bquery (out-of-core groupby’s): https://github.com/visualfabriq/bquery • Continuum’s Blaze: http://blaze.pydata.org/ • Quantopian: http://quantopian.github.io/talks/NeedForSpeed/ slides#/
- 39. bquery - On-Disk GroupBy In-memory (pandas) vs on-disk (bquery+bcolz) groupby “Switching to bcolz enabled us to have a much better scalable architecture yet with near in-memory performance” — Carst Vaartjes, co-founder visualfabriq
- 40. Quantopian’s Use Case “We set up a project to convert Quantopian’s production and development infrastructure to use bcolz” — Eddie Herbert
- 41. Closing Notes • If you need a data container that fits your needs, look for already nice libraries out there (NumPy, DyND, Pandas, PyTables, bcolz…) • Pay attention to hardware and software trends and make informed decisions in your current developments (which, btw, will be deployed in the future :) • Performance is needed for improving interactivity, so do not hesitate to optimize the hot spots in C if needed (via Cython or other means)
- 42. “It is change, continuing change, inevitable change, that is the dominant factor in Computer Sciences today. No sensible decision can be made any longer without taking into account not only the computer as it is, but the computer as it will be.” — Based on a quote by Isaac Asimov
- 43. Thank You!