Writing and Querying MapReduce Views in CouchDB

By Bradley Holt

If you need to use CouchDB to aid real-world purposes, you have to to create MapReduce perspectives that allow you to question this document-oriented database for significant facts. With this brief and concise book, you will the right way to create numerous MapReduce perspectives that will help you question and combination facts in CouchDB’s huge, disbursed datasets.

You'll get step by step directions and many pattern code to create and discover numerous MapReduce perspectives during the process the e-book, utilizing an instance database you build. To paintings with those diversified perspectives, you’ll methods to use the Futon internet management console and the cURL command line software that include CouchDB.

  • Learn how the Map and decrease steps paintings independently and jointly to index your data
  • Use the instance database to create numerous transitority perspectives in response to varied criteria
  • Discover the makes use of of Map and decrease JavaScript functions
  • Convert your transitority perspectives to everlasting perspectives inside of a layout document
  • Learn numerous concepts for querying the knowledge inside your views
  • Limit the variety of effects again, pass a few effects, or opposite the order of the output
  • Group your effects via unique keys or by means of components of keys

    Bradley Holt, co-founder of the artistic prone enterprise came across Line, is an internet developer and entrepreneur ten years of personal home page and MySQL event. He all started utilizing CouchDB ahead of the discharge of model 1.0. Bradley is an energetic member of the Hypertext Preprocessor group, and will be reached at bradley-holt.com.

Show description

Quick preview of Writing and Querying MapReduce Views in CouchDB PDF

Show sample text content

All parameters are non-compulsory. desk 4-1. View question innovations Parameter Description lessen If a lessen functionality is outlined, this parameter helps you to decide upon even if to run the lessen step. The default price is correct. startkey A URL encoded JSON price indicating the major at which to begin the variety. startkey_docid The identity of the rfile with which to begin the diversity. This parameter is, for all intents and reasons, missed whether it is now not utilized in conjunction with the startkey parameter. CouchDB will first examine the startkey parameter after which use the startkey_docid parameter to additional refine the start of the variety if a number of strength beginning rows have an identical key yet assorted record IDs.

Each one view on your database is saved as its personal B-tree index. CouchDB perspectives might be written to with out blockading learn operations. Write operations are serialized, yet concurrent learn operations are allowed. CouchDB will offer a constant view of the database to every and each learn operation. this is often accomplished by way of purely ever appending to the B-tree dossier on each one replace. the only exception to this append-only rule is the a part of the dossier containing the B-tree root node, that is overwritten on each one replace.

Making a transitority view of ebook codecs utilizing Futon with a decrease and unique grouping Or, utilizing cURL: curl -X submit http://localhost:5984/books/_temp_view? group=true \ -H "Content-Type: application/json" \ -d \ '{ "map": "function(doc) { if (doc. codecs) { for (var i in document. codecs) { emit(doc. formats[i]); } } }", "reduce": "_count" }' As you have guessed, the gang question string parameter controls even if to staff. utilizing CouchDB’s HTTP API, the default group_level is certain, so this parameter may be passed over.

Forty-one diversity Queries Rows by means of begin and finish Keys forty two forty three v Rows via Key Rows via begin and finish Keys and record IDs proscribing, Skipping, and Reversing effects restrict pass Reversing Output Grouping particular Grouping workforce degrees together with records vi | desk of Contents forty four forty five forty six forty seven forty eight forty nine 50 50 fifty two sixty one Preface Conventions utilized in This ebook the next typographical conventions are utilized in this e-book: Italic exhibits new phrases, URLs, electronic mail addresses, filenames, and dossier extensions.

Vii 1. creation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 assets for fitting CouchDB Futon HTTP API cURL JSON 1 1 2 three three 2. MapReduce . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . five transitority perspectives Map One-To-One Mapping One-To-Many Mapping end lessen count number Sum Stats customized decrease capabilities boundaries of MapReduce five 6 7 eleven 20 20 21 24 26 28 29 three. layout records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Titles View codecs View Authors View garage concerns 31 34 36 39 four.

Download PDF sample

Rated 4.24 of 5 – based on 30 votes