Couch db

Couch DB
Mohammad Hossain Amini
Advanced Database
Dr.Niyazi
1
2.0

CouchDB Is..
• An Apache Project.
• An Open-Source Document-Oriented Database.
• it uses JSON to store data.
• Written in Erlang.
• CouchDB project was created in April 2005 by Damien Katz.
• CouchDB became an Apache Software Foundation project in 2008.
• In early 2012, Katz left the project to focus on Couchbase Server.
3

Document Storage
• A CouchDB server hosts named databases, which store documents.
• CouchDB provides a RESTful HTTP API for reading and updating (add, edit, delete) database documents.
• Document fields are uniquely named and contain values of varying types (text, number, boolean, lists, etc).
• The CouchDB document update model is lockless and optimistic.
• CouchDB read operations use a Multi-Version Concurrency Control (MVCC).
• The database never contains partially saved or edited documents.
• Document updates (add, edit, delete) are serialized, except for binary blobs which are written concurrently.
• Documents are indexed in B-trees by their name (DocID) and a Sequence ID.
5

The CAP Theorem
• Consistency: All database clients see the same data, even with concurrent updates.
• Availability: All database clients are able to access some version of the data.
• Partition tolerance: The database can be split over multiple servers.
6

MapReduce Views
9
{ “user” : “Chris”,
“points” : 3 }
{ “user” : “Joe”,
“points” : 10 }
{ “user” : “Alice”,
“points” : 5 }
{ “user” : “Mary”,
“points” : 9 }
{ “user” : “Bob”,
“points” : 7 }
{ “key” : “Alice”,
“value” : 5 }
{ “key” : “Bob”,
“value” : 7 }
{ “key” : “Chris”,
“value” : 3 }
{ “key” : “Joe”,
“value” : 10 }
{ “key” : “Mary”,
“value” : 9 }
function(doc) {
if (doc.user && doc.points) {
emit(doc.user, doc.points);
}
}
MAP
Everyone: 34
function(keys, values, rereduce) {
return sum(values);
}
Reduce

Introduction to Replication
• One of CouchDB’s strengths is the ability to synchronize two copies of the same database.
• CouchDB will compare the source and the destination database(Changes Feeds).
• Master - Master replication.
• Local documents are never replicated (non-replicating).
• The document will only be replicated if the filter function returns true.
11

Migrating Data to Clients
• Cloudant
• PouchDB
• TouchDB
• Couchbase Lite
12

Document & Query
14
Document Query

16
http://127.0.0.1:5984/_utils/

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