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![Document Database
{
“_id” : “2d7f015226a05b6940984bbe39004fde”,
“_rev” : “2-477f6ab2dec6df185de1a078d270d8”,
“first_name” : “John”,
“last_name” : “Wood”,
“interests” : [“hacking”, “fishing”, “running”],
“offspring” : [
{ “name” : “Dylan”, “age” : 5 },
{ “name” : “Chloe”, “age” : 2 }
]
}
Monday, August 16, 2010](https://image.slidesharecdn.com/chidb-couchdb-100816161336-phpapp01/75/Introduction-to-CouchDB-4-2048.jpg)
Introduction to CouchDB
- 1. John Wood ChicagoDB User Group August 16, 2010 Monday, August 16, 2010
- 2. Outline • What is CouchDB? • Documents and Document Storage • Views • Replication • CouchApps • Add-ons • Resources • Demo! Monday, August 16, 2010
- 3. What is CouchDB? Monday,August 16, 2010
- 4. Document Database { “_id” : “2d7f015226a05b6940984bbe39004fde”, “_rev” : “2-477f6ab2dec6df185de1a078d270d8”, “first_name” : “John”, “last_name” : “Wood”, “interests” : [“hacking”, “fishing”, “running”], “offspring” : [ { “name” : “Dylan”, “age” : 5 }, { “name” : “Chloe”, “age” : 2 } ] } Monday, August 16, 2010
- 5. Strong Focus on Replication Monday, August 16, 2010 - Built from day one to support bi-directional peer to peer replication - This feature sets CouchDB apart from the other NoSQL databases, and makes it stand out in the database community
- 6. RESTful API # Create POST http://localhost:5984/employees # Read GET http://localhost:5984/employees/1 # Update PUT http://localhost:5984/employees/1 # Delete DELETE http://localhost:5984/employees/1 Monday, August 16, 2010
- 7. Queried and Indexed with MapReduce function(doc) { if (doc.first_name == “John”) emit(doc._id, 1); } function(keys, values, rereduce) { return sum(values); } Monday, August 16, 2010
- 8. Multiversion Concurrency Control http://en.wikipedia.org/wiki/Multiversion_concurrency_control Image: http://blogs.wyomingnews.com/blogs/everyonegives/files/2009/02/book-stack.jpg Monday, August 16, 2010 - Documents never updated in place; new revisions are always created - Advantages * Don't have to manage locks for reads. Don't have to worry about a concurrent update corrupting a read that is in progress. * Data is “safer”. Old revisions are kept around (at least for a while). If a botched update accidentally destroys data, you can always restore it from a previous revision. * The database can perform some optimizations when writing to disk. If creating or updating 1000 documents, those documents will all live next to each other on disk, eliminating disk seeks. - Disadvantages * Requires occasional database compaction
- 9. Ultra Durable Monday, August16, 2010 - When CouchDB documents are updated, all data and associated indexes are flushed to disk and the transactional commit always leaves the database in a completely consistent state. - 2 step commit: * All document data and associated index updates are synchronously flushed to disk. * The database header is written in two consecutive, identical chunks, and flushed to disk. - Crash recovery: * If crash on step 1 of commit, partially flushed data are forgotten upon restart. * If crash on step 2, a surviving copy of the previous headers will remain, and are used. - Crash only shutdown
- 10. Erlang OTP Monday, August16, 2010 The Erlang programming language and the OTP platform are known for their concurrency support, and OTP is known for its extreme emphasis on reliability and availability.
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- 12. Documents and Document Storage Monday, August 16, 2010
- 13. Documents • JSON data format • Schema-less • Support for binary data in the form of document “attachments” • Each document uniquely named in the database Monday, August 16, 2010
- 14. Document Storage • CouchDB uses append-only updates, and never overwrites comitted data • Document updates are serialized • Update model is lockless and optimistic • Reads are never blocked or interrupted by a concurrent updates • Databases require occasional compaction Monday, August 16, 2010
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- 16. Views • Add structure back to your unstructured data, so it can be queried • Allow you to have many different view representations of the same data • Created by executing map and reduce functions on your documents • View definitions are stored in Design Documents • Built incrementally and on demand Monday, August 16, 2010
- 17. MapReduce • MapReduce functions are written primarily in Javascript (some other languages are supported) • The map function selects which documents to operate on, emitting zero to many key/ value pairs to the reduce function • The (optional) reduce function combines the key/value pairs and performs any necessary calculations on that data Monday, August 16, 2010
- 18. View Indexes • View indexes are stored on disk separate from the main database, in a data structure specific to the given Design Document • Views are updated incrementally; only new/ changed documents are processed when the view is accessed • Building views (especially from scratch) can be time consuming and resource intensive for large databases Monday, August 16, 2010
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- 20. Replication • Effecient and reliable bi-directional replication • Only documents created/updated since the last replication are replicated • For each document, only updated fields are replicated • Support for one-time, continuous, and filtered replication • Fault tolerant - will simply pick up where it left off if something bad happens Monday, August 16, 2010
- 21. Conflict Management • Documents with conflicts have a property named “_conflicts”, which contains all conflicting revision ids • CouchDB chooses a winning document, but keeps losing documents around for manual conflict resolution • CouchDB does not attempt to merge conflicting documents • It is the application’s responsibility to make sure data is merged successfully • Losing documents will be removed upon compaction Monday, August 16, 2010
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- 23. What are CouchApps? • CouchApps are HTML and Javascript applications that can be hosted directly from CouchDB • CouchDB can serve HTML, images, CSS, Javascript, etc • Applications live in a Design Document, with static files (html, css, etc) as attachments • Dynamic behavior and database access done via Javascript • CouchDB can be a complete, local web platform • Support for virtual hosts and URL re-writing Monday, August 16, 2010
- 24. Why? • Your application and its associated data can be distributed, and replicated, together • If you like to share, somebody can grab your application and data with a single replication command • Not only Open Source, but Open Data as well • Applications can be taken off line, used, and updated data can be synchronized at a later point in time Monday, August 16, 2010
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- 30. Add-Ons • couchdb-lucene - Enables full text searching of documents using Lucene • GeoCouch - Adds support for geospacial queries to CouchDB • Lounge - A proxy-based partitioning/ clustering framework for CouchDB Monday, August 16, 2010
- 31. Resources • http://apache.couchdb.org • http://www.couch.io • http://wiki.apache.org/couchdb • http://books.couchdb.org/relax/ • http://wiki.couchapp.org Monday, August 16, 2010
- 32. Less Talk, MoreRock! Demo http://github.com/jwood/couchdb_demo Monday, August 16, 2010
- 33. Thanks! john_p_wood@yahoo.com @johnpwood Monday, August 16, 2010