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Compression Options in Hadoop - A Tale of Tradeoffs


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Yahoo! is one of the most-visited web sites in the world. It runs one of the largest private cloud infrastructures, one that operates on petabytes of data every day. Being able to store and manage that data well is essential to the efficient functioning of Yahoo!`s Hadoop clusters. A key component that enables this efficient operation is data compression. With regard to compression algorithms, there is an underlying tension between compression ratio and compression performance. Consequently, Hadoop provides support for several compression algorithms, including gzip, bzip2, Snappy, LZ4 and others. This plethora of options can make it difficult for users to select appropriate codecs for their MapReduce jobs. This paper attempts to provide guidance in that regard. Performance results with Gridmix and with several corpuses of data are presented. The paper also describes enhancements we have made to the bzip2 codec that improve its performance. This will be of particular interest to the increasing number of users operating on “Big Data” who require the best possible ratios. The impact of using the Intel IPP libraries is also investigated; these have the potential to improve performance significantly. Finally, a few proposals for future enhancements to Hadoop in this area are outlined.

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  • from what i understood, LZO was used for faster compression but at the cost of space. that is, compression is lesser but faster. but in slide 12, in the reduce face where we are supposed to compress more data as the file is written in order to save space, why are we using LZO compression 63% and gzip only 27%??
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Compression Options in Hadoop - A Tale of Tradeoffs

  1. 1. Compression Options In Hadoop – A Tale of Tradeoffs Govind Kamat, Sumeet Singh Hadoop Summit (San Jose), June 27, 2013
  2. 2. Introduction 2 Sumeet Singh Director of Products, Hadoop Cloud Engineering Group 701 First Avenue Sunnyvale, CA 94089 USA Govind Kamat Technical Yahoo!, Hadoop Cloud Engineering Group  Member of Technical Staff in the Hadoop Services team at Yahoo!  Focuses on HBase and Hadoop performance  Worked with the Performance Engineering Group on improving the performance and scalability of several Yahoo! applications  Experience includes development of large-scale software systems, microprocessor architecture, instruction-set simulators, compiler technology and electronic design 701 First Avenue Sunnyvale, CA 94089 USA  Leads Hadoop products team at Yahoo!  Responsible for Product Management, Customer Engagements, Evangelism, and Program Management  Prior to this role, led Strategy functions for the Cloud Platform Group at Yahoo!
  3. 3. Agenda 3 Data Compression in Hadoop1 Available Compression Options2 Understanding and Working with Compression Options3 Problems Faced at Yahoo! with Large Data Sets4 Performance Evaluations, Native Bzip2, and IPP Libraries5 Wrap-up and Future Work6
  4. 4. Compression Needs and Tradeoffs in Hadoop 4  Storage  Disk I/O  Network bandwidth  CPU Time  Hadoop jobs are data-intensive, compressing data can speed up the I/O operations  MapReduce jobs are almost always I/O bound  Compressed data can save storage space and speed up data transfers across the network  Capital allocation for hardware can go further  Reduced I/O and network load can bring significant performance improvements  MapReduce jobs can finish faster overall  On the other hand, CPU utilization and processing time increases during decompression  Understanding the tradeoffs is important for MapReduce pipeline’s overall performance The Compression Tradeoff
  5. 5. Data Compression in Hadoop’s MR Pipeline 5 Input splits Map Source: Hadoop: The Definitive Guide, Tom White Output ReduceBuffer in memory Partition and Sort fetch Merge on disk Merge and sort Other maps Other reducers I/P compressed Mapper decompresses Mapper O/P compressed 1 Map Reduce Reduce I/P Map O/P Reducer I/P decompresses Reducer O/P compressed 2 3 Shuffle & Sort Compress Decompress
  6. 6. Compression Options in Hadoop (1/2) 6 Format Algorithm Strategy Emphasis Comments zlib Uses DEFLATE (LZ77 and Huffman coding) Dictionary-based, API Compression ratio Default codec gzip Wrapper around zlib Dictionary-based, standard compression utility Same as zlib, codec operates on and produces standard gzip files For data interchange on and off Hadoop bzip2 Burrows-Wheeler transform, MTF Transform-based, block-oriented Higher compression ratios than zlib Common for Pig LZO Variant of LZ77 Dictionary-based, block-oriented, API High compression speeds Common for intermediate compression, HBase tables LZ4 Simplified variant of LZ77 Fast scan, API Very high compression speeds Available in newer Hadoop distributions Snappy LZ77 Block-oriented, API Very high compression speeds Came out of Google, previously known as Zippy
  7. 7. Compression Options in Hadoop (2/2) 7 Format Codec (Defined in io.compression.codecs) File Extn. Splittable Java/ Native zlib/ DEFLATE (default) .deflate N Y/ Y gzip .gz N Y/ Y bzip2 .bz2 Y Y/ Y LZO (download separately) com.hadoop.compression.lzo.LzoCodec .lzo N N/ Y LZ4 .lz4 N N/ Y Snappy .snappy N N/ Y NOTES:  Splittability – Bzip2 is “splittable”, can be decompressed in parallel by multiple MapReduce tasks. Other algorithms require all blocks together for decompression with a single MapReduce task.  LZO – Removed from Hadoop because the LZO libraries are licensed under the GNU GPL. LZO format is still supported and the codec can be downloaded separately and enabled manually.  Native bzip2 codec – added by Yahoo! as part of this work in Hadoop 0.23
  8. 8. Space-Time Tradeoff of Compression Options 8 64%, 32.3 71%, 60.0 47%, 4.842%, 4.0 44%, 2.4 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 40% 45% 50% 55% 60% 65% 70% 75% CPUTimeinSec. (Compress+Decompress) Space Savings Bzip2 Zlib (Deflate, Gzip) LZOSnappy LZ4 Note: A 266 MB corpus from Wikipedia was used for the performance comparisons. Space savings is defined as 1- (Compressed/ Uncompressed) Codec Performance on the Wikipedia Text Corpus High Compression Ratio High Compression Speed
  9. 9. Using Data Compression in Hadoop 9 Phase in MR Pipeline Config Values Input data to Map File extension recognized automatically for decompression File extensions for supported formats Note: For SequenceFile, headers have the information [compression (boolean), block compression (boolean), and compression codec] One of the supported codecs one defined in io.compression.codecs Intermediate (Map) Output false (default), true one defined in io.compression.codecs Final (Reduce) Output mapreduce.output.fileoutputformat. compress false (default), true mapreduce.output.fileoutputformat. compress.codec one defined in io.compression.codecs mapreduce.output.fileoutputformat. compress.type Type of compression to use for SequenceFile outputs: NONE, RECORD (default), BLOCK 1 2 3
  10. 10.  Compress the input data, if large  Always use compression, particularly if spillage or slow network transfers  Compress for storage/ archival, better write speeds, or chained MR jobs  Use splittable algo such as bzip2, or use zlib with SequenceFile format  Use faster codecs such as LZO, LZ4, or Snappy  Use standard utility such as gzip or bzip2 for data interchange When to Use Compression and Which Codec 10 Map ReduceShuffle & Sort Input data to Map Intermediate (Map) Output I/P compressed Mapper decompresses Mapper O/P compressed 1 Reducer I/P decompresses Reducer O/P compressed 2 3 Compress Decompress Final Reduce Output
  11. 11. Compression in the Hadoop Ecosystem 11 Component When to Use What to Use Pig  Compressing data between MR job  Typical in Pig scripts that include joins or other operators that expand your data size Enable compression and select the codec: pig.tmpfilecompression = true pig.tmpfilecompression.codec = gzip, lzo Hive  Intermediate files produced by Hive between multiple map- reduce jobs  Hive writes output to a table Enable intermediate or output compression: hive.exec.compress.intermediate = true hive.exec.compress.output = true HBase  Compress data at the CF level (support for LZO, gzip, Snappy, and LZ4) List required JNI libraries: hbase.regionserver.codecs Enabling compression: create ’table', { NAME => 'colfam', COMPRESSION => ’LZO' } alter ’table', { NAME => 'colfam', COMPRESSION => ’LZO' }
  12. 12. Compression in Hadoop at Yahoo! 12 96% 4% lzo 98.03% gzip 0.99% zlib/ default 0.70% bzip2 0.05% 18M Jobs, May 2013 Map ReduceShuffle & Sort Input data to Map Intermediate (Map) Output 1 2 3 Final Reduce Output 41% 59% lzo 63% gzip 27% bzip2 6% default 4% 18M Jobs, May 2013 98% 2% zlib/ default 73% gzip 22% bzip2 4% Lzo 1% 380M Files on Jun 16, 2013 (/data, /projects) Included intermediate Pig/ Hive compression Pig Intermediate
  13. 13. Compression for Data Storage Efficiency  Need to improve data storage efficiency at Yahoo!  Switch from SequenceFile to RCFile  Considered using bzip2 for improved compression ratio  Alternative library to compensate for compression effort  However, Hadoop codec is implemented in pure-Java  Had to re-implement it to call into the native-code library  HADOOP-84621, available in 0.23.7  Next step was to have the codec load the IPP library 13 1 Native-code bzip2 implementation done in collaboration with Jason Lowe, Hadoop Core PMC member
  14. 14. IPP Libraries  Integrated Performance Primitives from Intel  Includes both algorithmic and architectural optimizations  Applications remain processor-neutral  Processor-specific variants of each function  Compression: LZ, RLE, BWT, LZO  High level formats include: zlib, gzip, bzip2 and LZO 14
  15. 15. Measuring Standalone Performance  Standard utilities (gzip, bzip2) used where available  Driver program written for other cases  32-bit mode  JVM load overhead discounted  Single-threaded  Default compression level  Quad-core Xeon machine 15
  16. 16. Data Corpuses Used  Binary files  Generated text from randomtextwriter  Wikipedia corpus  Silesia corpus 16
  17. 17. Compression Ratio 0 50 100 150 200 250 300 uncomp zlib bzip2 LZO Snappy LZ4 FileSize(MB) exe rtext wiki silesia 17
  18. 18. Compression Performance 29 23 63 44 26 0 10 20 30 40 50 60 70 80 90 zlib IPP-zlib Java-bzip2 bzip2 IPP-bzip2 CPUTime(sec) exe rtext wiki silesia 18
  19. 19. Compression Performance (Fast Algorithms) 3.2 2.9 1.7 0 0.5 1 1.5 2 2.5 3 3.5 LZO Snappy LZ4 CPUTime(sec) exe rtext wiki silesia 19
  20. 20. Decompression Performance 3 2 21 17 12 0 5 10 15 20 25 zlib IPP-zlib Java-bzip2 bzip2 IPP-bzip2 CPUTime(sec) exe rtext wiki silesia 20
  21. 21. Decompression Performance (Fast Algorithms) 1.6 1.1 0.7 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 LZO Snappy LZ4 CPUTime(sec) exe rtext wiki silesia 21
  22. 22. Compression Performance within Hadoop  Daytona performance framework  Used GridMix v1  Loadgen and sort jobs used  Input data in the following compression modes:  Compressed with zlib  Compressed with bzip2  LZO used for intermediate compression  35 datanodes, dual-quad-core machines 22
  23. 23. Map Performance 47 46 46 33 0 5 10 15 20 25 30 35 40 45 50 Java-bzip2 bzip2 IPP-bzip2 zlib MapTime(sec) 23
  24. 24. Reduce Performance 31 28 18 14 0 5 10 15 20 25 30 35 Java-bzip2 bzip2 IPP-bzip2 zlib ReduceTime(min) 24
  25. 25. Job Performance 38 34 23 19 38 34 25 18 0 5 10 15 20 25 30 35 40 Java-bzip2 bzip2 IPP-bzip2 zlib JobTime(min) sort loadgen 25
  26. 26. Future Work  Splittability support for native-code bzip2 codec  Enhancing Pig to use common bzip2 codec  Optimizing the JNI interface and buffer copies  Performance evaluation for 64-bit mode  Varying the compression effort parameter  Updating the zlib codec to specify alternative libraries  Other codec combinations, such as zlib for transient data  Other compression algorithms 26
  27. 27. Considerations in Selecting Compression Type  Nature of the data set  Frequency of compression vs. decompression  Data-storage efficiency requirements  Requirement for compatibility with a standard data format  Splittability requirements  Machine architecture, whether 32-bit or 64-bit  Size of the intermediate and final data  Alternative implementations of compression libraries 27