Bigtable

Bigtable is a compressed, high performance, proprietary data storage system built on Google File System, Chubby Lock Service, SSTable (log-structured storage like LevelDB) and a few other Google technologies. On May 6, 2015, a public version of Bigtable was made available as a service. Bigtable also underlies Google Cloud Datastore, which is available as a part of the Google Cloud Platform.[1][2]

Google Bigtable
Developer(s)Google
Initial releaseFebruary 2005 (2005-02)
Written in
C++ (core), Java, Python, Go, Ruby
PlatformGoogle Cloud Platform
TypeCloud Storage
LicenseProprietary
Websitecloud.google.com/bigtable/

History

Bigtable development began in 2004[3] and is now used by a number of Google applications, such as web indexing,[4] MapReduce, which is often used for generating and modifying data stored in Bigtable,[5] Google Maps,[6] Google Book Search, "My Search History", Google Earth, Blogger.com, Google Code hosting, YouTube,[7] and Gmail.[8] Google's reasons for developing its own database include scalability and better control of performance characteristics.[9]

Google's Spanner RDBMS is layered on an implementation of Bigtable with a Paxos group for two-phase commits to each table. Google F1 was built using Spanner to replace an implementation based on MySQL.[10]

Design

Bigtable is one of the prototypical examples of a wide column store. It maps two arbitrary string values (row key and column key) and timestamp (hence three-dimensional mapping) into an associated arbitrary byte array. It is not a relational database and can be better defined as a sparse, distributed multi-dimensional sorted map.[4]:1 Bigtable is designed to scale into the petabyte range across "hundreds or thousands of machines, and to make it easy to add more machines [to] the system and automatically start taking advantage of those resources without any reconfiguration".[11] For example, Google's copy of the web can be stored in a bigtable where the row key is a domain-reversed URL, and columns describe various properties of a web page, with one particular column holding the page itself. The page column can have several timestamped versions describing different copies of the web page timestamped by when they were fetched. Each cell of a bigtable can have zero or more timestamped versions of the data. Another function of the timestamp is to allow for both versioning and garbage collection of expired data.

Tables are split into multiple tablets – segments of the table are split at certain row keys so that each tablet is a few hundred megabytes or a few gigabytes in size. A bigtable is somewhat like a mapreduce worker pool in that thousands to hundreds of thousands of tablet shards may be served by hundreds to thousands of BigTable servers. When Table size threaten to grow beyond a specified limit, the tablets may be compressed using the algorithm BMDiff[12][13] and the Zippy compression algorithm[14] publicly known and open-sourced as Snappy,[15] which is a less space-optimal variation of LZ77 but more efficient in terms of computing time. The locations in the GFS of tablets are recorded as database entries in multiple special tablets, which are called "META1" tablets. META1 tablets are found by querying the single "META0" tablet, which typically resides on a server of its own since it is often queried by clients as to the location of the "META1" tablet which itself has the answer to the question of where the actual data is located. Like GFS's master server, the META0 server is not generally a bottleneck since the processor time and bandwidth necessary to discover and transmit META1 locations is minimal and clients aggressively cache locations to minimize queries.

See also

References
  1. "Announcing Google Cloud Bigtable: The same database that powers Google Search, Gmail and Analytics is now available on Google Cloud Platform". Google Blog. 6 May 2015. Retrieved 21 September 2016.
  2. "Get started with Google Cloud Datastore - a fast, powerful, NoSQL database".
  3. Hitchcock, Andrew, Google's Bigtable, retrieved 29 July 2007, First an overview. Bigtable has been in development since early 2004 and has been in active use for about eight months (about February 2005)..
  4. Chang et al. 2006.
  5. Chang et al. 2006, p. 3: ‘Bigtable can be used with MapReduce, a framework for running large-scale parallel computations developed at Google. We have written a set of wrappers that allow a Bigtable to be used both as an input source and as an output target for MapReduce jobs’
  6. Hitchcock, Andrew, Google's Bigtable, retrieved 29 July 2007, There are currently around 100 cells for services such as Print, Search History, Maps, and Orkut.
  7. Cordes, Kyle (12 July 2007), YouTube Scalability (talk), Their new solution for thumbnails is to use Google’s Bigtable, which provides high performance for a large number of rows, fault tolerance, caching, etc. This is a nice (and rare?) example of actual synergy in an acquisition..
  8. "How Entities and Indexes are Stored", Google App Engine, Google Code.
  9. Chang et al. 2006, Conclusion: ‘We have described Bigtable, a distributed system for storing structured data at Google... Our users like the performance and high availability provided by the Bigtable implementation, and that they can scale the capacity of their clusters by simply adding more machines to the system as their resource demands change over time... Finally, we have found that there are significant advantages to building our own storage solution at Google. We have gotten a substantial amount of flexibility from designing our own data model for Bigtable.’
  10. Shute, Jeffrey ‘Jeff’; Oancea, Mircea; Ellner, Stephan; Handy, Benjamin ‘Ben’; Rollins, Eric; Samwel, Bart; Vingralek, Radek; Whipkey, Chad; Chen, Xin; Jegerlehner, Beat; Littlefield, Kyle; Tong, Phoenix (2012), "Summary; F1 — the Fault-Tolerant Distributed RDBMS Supporting Google's Ad Business", Research (presentation), Sigmod, p. 19, We've moved a large and critical application suite from MySQL to F1.
  11. "Google File System and Bigtable", Radar (World Wide Web log), Database War Stories, O’Reilly, May 2006.
  12. "Google Bigtable, Compression, Zippy and BMDiff". 12 October 2008. Archived from the original on 1 May 2013. Retrieved 14 April 2015..
  13. McIlroy, Bentley. Data compression using long common strings. DCC '99. IEEE. doi:10.1109/DCC.1999.755678..
  14. "Google's Bigtable", Outer court (Weblog), 23 October 2005.
  15. "Snappy", Code (project).

Bibliography
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