apache couchdb

Apache CouchDB

Course: Advanced DatabasesGroup 5: Trinh Phuc Tho, Vo Quoc Khanh, Hoang Trung Hieu

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What to expect?

Technical Overview

Consistency Model

Live Demo

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Technical Overview

Document Storage

ACID Properties

Compaction

Views

Distributed Updates

Conflict Resolution

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Technical Overview

So, wtf is CouchDB?

NoSQL databases

document store

distributed architecture

easy replication

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Technical Overview

Document Storage

use append-only files

documents stored as JSON

access via RESTful HTTP API

map-reduce functions (Javascript) for views

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Technical Overview

ACID Properties

commitment system features all ACID properties

never overwrite committed data (append-only)

no shutdown process

no “repair” command needed (Clap!!!)

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Technical Overview

ACID Properties (2)

document updates are serialized

readers never have to wait on writers, even on the same document

Multi-version Concurrency Control (MVCC)

additional sequence IDs (_rev) are used

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Technical Overview

ACID Properties (3)

2-step commit:Step 1: Document data & associated index updates are

flushed to disk (append to file).Step 2: The updated database header is written in

two consecutive, identical chunksto make up the first 4 KB of the file

Handling failures:Case 1: Partially flushed updates are simply ignoredCase 2: The surviving copy is used

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Technical Overview

ACID Properties (3)

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Technical Overview

Compaction

data cloned to a new file

redundant data are removed

no downtime required

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Technical Overview

Views

allow aggregating and reporting on documents

use Javascript map-reduce functions

view indexes are built only once and updated incrementally

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Technical Overview

Distributed Updates

Peer-based distributed database system

Incremental replication(partial replication is allowed)

Peers access & update the same data while disconnected need for conflict resolution after replication

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Technical Overview

Conflict Resolution

allow for decentralized conflict resolution

preserve single document semantics

conflicting documents are also replicated

after replication, one revision will be picked as the “winner” by a deterministic algorithm so that the same choice will be made on all peers

other revisions are marked as _deleted, and will not be removed during compaction.

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Technical Overview

Conflict Resolution (2)

Get conflicting revisions:GET /db/doc_id?conflicts=true

Fetch a history revision:GET /db/doc_id?rev=xxxx

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Consistency Model

The CAP theorem

Local Consistency

Validation

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Consistency Model

The CAP Theorem

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Consistency Model

Local Consistency

No Locking

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Consistency Model

Validation

Javascript functions are used for validation Context information is provided Updates can be approved or denied

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Live Demo

CRUD

Views

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References

Apache CouchDB 1.6 documentationhttp://docs.couchdb.org/en/1.6.x/

Karel Minařík presentation at WebExpo2010http://webexpo.net/prague2010/talk/couchdb-database-for-the-web/

Introduction to REST & CouchDB, ULM Universityhttp://www.slideshare.net/partlycloudy/introduction-to-rest-couchdb

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