1. 2 App Designs
Using MongoDB

2. Kyle Banker
kyle@10gen.com

3. @hwaet

4. What we'll cover:
Brief intro
Feed reader
Website analyitcs
Questions

5. Intro

6. MongoDB
Rich data model
Replication and automatic failover
Sharding

7. Use cases
Social networking and geolocation
E-commerce
CMS
Analytics
Production deployments: http://is.gd/U0VkG6

8. Demo

9. Feed reader

10. Four collections
Users
Feeds
Entries
Buckets

11. Users
{ _id: ObjectId("4e316f236ce9cca7ef17d59d"),
username: 'kbanker',
feeds: [
{ _id: ObjectId("4e316f236ce9cca7ef17d54c"),
name: "GigaOM" },
{ _id: ObjectId("4e316f236ce9cca7ef17d54d"),
name: "Salon.com" }
{ _id: ObjectId("4e316f236ce9cca7ef17d54e"),
name: "Foo News" }
],
latest: Date(2011, 7, 25)
}

12. Index
db.users.ensureIndex( { username: 1 }, { unique: true } )

13. Feeds
{ _id: ObjectId("4e316b8a6ce9cca7ef17d54b"),
url: 'http://news.foo.com/feed.xml/',
name: 'Foo News',
subscriber_count: 2,
latest: Date(2011, 7, 25)
}
Index
db.feeds.ensureIndex( { url: 1 }, { unique: true

14. Adding a feed subscription
// Upsert
db.feeds.update(
{ url: 'http://news.foo.com/feed.xml/', name: 'Foo News'},
{ $inc: {subscriber_count: 1} },
true )

15. Adding a feed subscription
// Add this feed to user feed list
db.users.update( {_id: ObjectId("4e316f236ce9cca7ef17d59d") },
{ $addToSet: { feeds:
{ _id: ObjectId("4e316b8a6ce9cca7ef17d54b"),
name: 'Foo News'
}
}
)

16. Removing a feed
subscription
db.users.update(
{ _id: ObjectId("4e316f236ce9cca7ef17d59d") },
{ $pull: { feeds:
{ _id: ObjectId("4e316b8a6ce9cca7ef17d54b"),
name: 'Foo News'
}
} )

17. Removing a feed
subscription
db.feeds.update( {url: 'http://news.foo.com/feed.xml/'},
{ $inc: {subscriber_count: -1} } )

18. Entries (populate in
background)
{ _id: ObjectId("4e316b8a6ce9cca7ef17d54b"),
feed_id: ObjectId("4e316b8a6ce9cca7ef17d54b"),
title: 'Important person to resign',
body: 'A person deemed very important has decided...',
reads: 5,
date: Date(2011, 7, 27)
}

19. What we need now
Populate personal feeds (buckets)
Avoid lots of expensive queries
Record what's been read

20. Without bucketing
// Naive query runs every time
db.entries.find(
feed_id: {$in: user_feed_ids}
).sort({date: 1}).limit(25)

21. With bucketing
// A bit smarter: only runs once
entries = db.entries.find(
{ date: {$gt: user_latest },
feed_id: { $in: user_feed_ids }
).sort({date: 1})

22. Index
db.entries.ensureIndex( { date: 1, feed_id: 1} )

23. bucket = {
_id: ObjectId("4e3185c26ce9cca7ef17d552"),
user_id: ObjectId("4e316f236ce9cca7ef17d59d"),
date: Date( 2011, 7, 27 )
n: 100,
entries: [
{ _id: ObjectId("4e316b8a6ce9cca7ef17d5ac"),
feed_id: ObjectId("4e316b8a6ce9cca7ef17d54b"),
title: 'Important person to resign',
body: 'A person deemed very important has decided...',
date: Date(2011, 7, 27),
read: false
},
{ _id: ObjectId("4e316b8a6ce9cca7ef17d5c8"),
feed_id: ObjectId("4e316b8a6ce9cca7ef17d54b"),
title: 'Panda bear waves hello',
body: 'A panda bear at the local zoo...',
date: Date(2011, 7, 27),
read: false
}
]
}

24. db.buckets.insert( buckets )
db.users.update(
{ _id: ObjectId("4e316f236ce9cca7ef17d59d") }
{ $set: { latest: latest_entry_date } }
)

25. Viewing a personal feed
// Newest
db.buckets.find(
{ user_id: ObjectId("4e316f236ce9cca7ef17d59d") }
).sort({date: -1}).limit(1)

26. Viewing a personal feed
// Next newest (that's how we paginate)
db.buckets.find(
{ user_id: ObjectId("4e316f236ce9cca7ef17d59d"),
date: { $lt: previous_reader_date }
}
).sort({date: -1}).limit(1)

27. Index
db.buckets.ensureIndex( { user_id: 1, date: -1 } )

28. Marking a feed item
db.buckets.update(
{ user_id: ObjectId("4e316f236ce9cca7ef17d59d"),
'entries.id': ObjectId("4e316b8a6ce9cca7ef17d5c8")},
{ $set: { 'entries.$.read' : true }
)

29. Marking a feed item
db.entries.update(
{ _id: ObjectId("4e316b8a6ce9cca7ef17d5c8") },
{ $inc: { read: 1 } }
)

30. Sharding note:
Buckets collection is eminently shardable
Shard key: { user_id: 1, date: 1 }

31. Website
analyitcs

32. Challenges:
Real-time reporting.
Efficient use of space.
Easily wipe unneeded data.

33. Techniques
Pre-aggregate the data.
Pre-construct document structure.
Store emphemeral data in a separate
database.

34. Two collections:
Each collection gets its own database.
Collections names are time-scoped.
Clean, fast removal of old data.

35. // Collections holding totals for each day, stored
// in a database per month
days_2011_5
days_2011_6
days_2011_7
...
// Totals for each month...
months_2011_1_4
months_2011_5_8
months_2011_9_12
...

36. Hours and minutes
{ _id: { uri: BinData("0beec7b5ea3f0fdbc95d0dd47f35"),
day: '2011-5-1'
},
total: 2820,
hrs: { 0: 500,
1: 700,
2: 450,
3: 343,
// ... 4-23 go here
}
// Minutes are rolling. This gives real-time
// numbers for the last hour. So when you increment
// minute n, you need to $set minute n-1 to 0.
mins: { 1: 12,
2: 10,
3: 5,
4: 34
// ... 5-60 go here
}
}

37. Updating day
document...

38. // Update 'days' collection at 5:37 p.m. on 2011-5-1
// Might want to queue increments so that $inc is greater
// than 1 for each write...
id = { uri: BinData("0beec7b5ea3f0fdbc95d0dd47f35"),
day: '2011-5-1'
};
update = { $inc: { total: 1, 'hrs.17': 1, 'mins.37': 1 },
$set: { 'mins.36': 0} };
// Update collection containing days 1-5
db.days_2011_5.update( id, update );

39. Months and days
{ _id: { uri: BinData("0beec7b5ea3f0fdbc95d0dd47f35"),
month: '2011-5'
},
total: 34173,
months: { 1: 4000,
2: 4300,
3: 4200,
4: 5000,
5: 5100,
6: 5700,
7: 5873
// ... 8-12 go here
}
}

40. Updating month
document...

41. // Update 'months' collection at 5:37 p.m. on 2011-5-1
query = { uri: BinData("0beec7b5ea3f0fdbc95d0dd47f35"),
month: '2011-5'
};
update = { $inc: { total: 1, 'months.5': 1 } };
// Update collection containing days 1-5
db.month_2011_1_4.update( query, update );

42. Reporting
Must provide data at multiple resolutions
(second, minute, etc.).
We have the raw materials for that.
Application assembles the data
intelligently.

43. Summary

44. Feed Reader
Rich documents
Incremental modifiers
Bucketing strategy

45. Website Analytics
Pre-aggregate data
Time-scoped databases and collections

46. http://www.10gen.com/presentations

47. http://manning.com/banker

48. Thank you