MongoDB EuroPython 2009

open-source, high-performance, schema-free, document-oriented database

RDBMS • Great for many applications • Shortcomings • Scalability • Flexibility

CAP Theorem • Consistency • Availability • Tolerance to network Partitions • Pick two http://www.cs.berkeley.edu/~brewer/cs262b-2004/PODC-keynote.pdf

ACID vs BASE • Atomicity • Basically Available • Consistency • Soft state • Isolation • Eventually consistent • Durability

Schema-free • Loosening constraints - added ﬂexibility • Dynamically typed languages • Migrations

BigTable • Single master node • Row / Column hybrid • Versioned

BigTable • Open-source clones: • HBase • Hypertable

Dynamo • Simple Key/Value store • No master node • Write to any (many) nodes • Read from one or more nodes (balance speed vs. consistency) • Read repair

Dynamo • Open-source clones • Project Voldemort • Cassandra - data model more like BigTable • Dynomite

memcached • Used as a caching layer • Essentially a key/value store • RAM only - fast • Does away with ACID

Redis • Like memcached • Different • Values can be strings, lists, sets • Non-volatile

Tokyo Cabinet + Tyrant • Key/value store with focus on speed • Some more advanced queries • Sorting, range or preﬁx matching • Multiple storage engines • Hash, B-Tree, Fixed length and Table

• A lot in common with MongoDB: • Document-oriented • Schema-free • JSON-style documents

• Differences • MVCC based • Replication as path to scalability • Query through predeﬁned views • ACID • REST

• Focus on performance • Rich dynamic queries • Secondary indexes • Replication / failover • Auto-sharding • Many platforms / languages supported

Good at • The web • Caching • High volume / low value • Scalability

Less good at • Highly transactional • Ad-hoc business intelligence • Problems that require SQL

PyMongo • Python driver for MongoDB • Pure Python, with optional C extension • Installation (setuptools): easy_install pymongo

Document • Unit of storage (think row) • Just a dictionary • Can store many Python types: • None, bool, int, ﬂoat, string / unicode, dict, datetime.datetime, compiled re • Some special types: • SON, Binary, ObjectId, DBRef

Collection • Schema-free equivalent of a table • Logical groups of documents • Indexes are per-collection

_id • Special key • Present in all documents • Unique across a Collection • Any type you want

Blog back-end

Post {“author”: “mike”, “date”: datetime.datetime.utcnow(), “text”: “my blog post...”, “tags”: [“mongodb”, “python”]}

Comment {“author”: “eliot”, “date”: datetime.datetime.utcnow(), “text”: “great post!”}

New post post = {“author”: “mike”, “date”: datetime.datetime.utcnow(), “text”: “my blog post...”, “tags”: [“mongodb”, “python”]} post_id = db.posts.save(post)

Embedding a comment c = {“author”: “eliot”, “date”: datetime.datetime.utcnow(), “text”: “great post!”} db.posts.update({“_id”: post_id}, {“$push”: {“comments”: c}})

Last 10 posts query = db.posts.find() .sort(“date”, DESCENDING) .limit(10) for post in query: print post[“text”]

Posts by author db.posts.find({“author”: “mike”})

Posts in the last week last_week = datetime.datetime.utcnow() + datetime.timedelta(days=-7) db.posts.find({“date”: {“$gt”: last_week}})

Posts ending with ‘Python’ db.posts.find({“text”: re.compile(“Python$”)})

Posts with a tag db.posts.find({“tag”: “mongodb”}) ... and fast db.posts.create_index(“tag”, ASCENDING)

Counting posts db.posts.count() db.posts.find({“author”: “mike”}).count()

Basic paging page = 2 page_size = 15 db.posts.find().limit(page_size) .skip(page * page_size)

Migration: adding titles • Easy - just start adding them: post = {“author”: “mike”, “date”: datetime.datetime.utcnow(), “text”: “another blog post...”, “tags”: [“meetup”, “python”], “title”: “Document Oriented Dbs”} post_id = db.posts.save(post)

Advanced queries • $gt, $lt, $gte, $lte, $ne, $all, $in, $nin • where() db.posts.find().where(“this.author == ‘mike’”) • group()

Other cool stuff • Capped collections • Unique indexes • Mongo shell • GridFS • MongoKit (on pypi)

• Download MongoDB http://www.mongodb.org • Install PyMongo • Try it out!

• http://www.mongodb.org • irc.freenode.net#mongodb • mongodb-user on google groups • @mongodb, @mdirolf • mike@10gen.com • http://www.slideshare.net/mdirolf

http://www.slideshare.net	55
http://redcloverbi.wordpress.com	43
http://www.thesavvyguideto.com	25
http://lj-toys.com	7
http://denkyem.posterous.com	6
http://l.lj-toys.com	3
http://hnourel.posterous.com	2
http://hnourel.blogspot.com	1
http://www.techgig.com	1
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MongoDB EuroPython 2009

by Mike Dirolf

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