This document summarizes key information about Saavn, India's largest music streaming service. Some key points: - Saavn has 18 million global monthly active users, with 14 million in India. The majority (64%) use Android devices to access over 25 million tracks. - Push notifications are a primary driver of mobile app growth for Saavn. They send over 30 million notifications per day and see 3x more engagement from targeted notifications. - Saavn stores user notification messages and activity data in MongoDB. They upgraded to WiredTiger for its document locking and high performance. Maintaining over 500GB of user data required implementing sharding and migrating the data. - Tools like

1. MAY 2016

2. Sri Manjunath
CTO, Saavn

3. I N D I A ’ S M U S I C S T R E A M I N G S E R V I C E
Saavn
3

4. SECTION
2nd biggest smartphone market
4 billion $ in VC funding in 2015
2 M phones sold per month
4
India = Mobile
…what does it look like?

5. SECTION5
Saturday phone shopping

6. By the numbers…
• 18 M Global MAUs
• 300 M streams a month
• 14 M India MAUs
• 25+ M tracks on Saavn
• 9x DAU growth in 24 Months

7. 18%
64%
8%
11%
Web iOS Android Mobile Web
7
GLOBAL MAUS
• 64% on Android
• 63% streams on mobile data
• ~50% of registrations via Phone
numbers
90% of our Users are on Mobile

8. 8
S U B S E C T I O N
Group
Top Music Streaming Apps by Active Users,
iPhone & Android, 2015
SOURCE: APP ANNIE, 2015 ©8

9. S U B S E C T I O N
MongoDB’s role

10. 10
P U S H N O T I F I C A T I O N S , E M A I L S A N D A D S
Goal: System to target users

11. 11
Targetable features
GEO
A R T I S T S A N D
GENRES TIME BAND
FITNESS
ENTHUSIASTGENDER
D E V I C E SOPERATING
SY STE M
INTERNATIONAL
TRAVELERS

12. Push notifications
Primary growth driver for mobile apps
Send 30+ million every day
Targeted notifications get 3x more
CTRs

13. Dispatch push notifications AND store
them in an inbox
Deliver at users local time
Context is key - delivery should be fast!
Update millions of notification inboxes
while serving traffic
Identify cohorts in real time
Delete ‘expired’ notifications
System characteristics

14. Architecture

15. System characteristics
Dispatch push notifications AND store
them in an inbox
Deliver at users local time
Context is key - delivery should be fast!
Update millions of notification
inboxes while serving traffic
Identify cohorts in real time
Delete ‘expired’ notifications

16. SECTION
• Move to WiredTiger
• Upgrade was surprisingly simple
• Supports mixed engine clusters
16
Need granular locks

17. Inbox Schema
Pluses
• 1 document per user
• Use push/slice to add messages to the
document
• Delete expired messages at the app
layer
Minuses
• Horrible performance on WiredTiger
• Too many updates
{
_id: "",
uid: "",
messages: [
mid_1 : {
text: "Message 1",
deeplink: "saavn://message_1",
image: "...."
},
mid_2: {
text: "Message 2",
deeplink: "saavn://message_2",
image: "...."
},
mid_3: {
text: "Message 3",
deeplink: "saavn://message_3",
image: "...."
},
......
]
}

18. Take 2 - Referencing
Pluses:
• No updates
• TTLs can delete older records
Minuses:
• Two queries per user
Inbox entries
{
_id: "Obj_1",
mid : "mid_1",
text: "Message 1",
deeplink: "saavn://
message_1",
image: "...."
},
{
_id: "Obj_2",
mid : "mid_2",
text: "Message 2",
deeplink: "saavn://
message_2",
image: "...."
},
.....
Inbox map
{
_id: "",
uid: "",
mid_obj : "Obj_1",
}
{
_id: "",
uid: "",
mid_obj : "Obj_2"
},
.....

19. INBOX SCHEMA19

21. Key Learnings
Upgrade to WiredTiger. Document locks are worth it.
Ungroup data
TTLs are a boon to temporary data.
WiredTiger uses Copy On Write
WiredTiger updates are expensive - avoid push/slice operation.
Optimize indexes based on the access pattern.
Use Provisioned IOPS on AWS

22. Architecture

23. User activity store
18+ M MAU, 40 min avg session time => lot of data!
Measuring listening activity is critical
Bursty writes and frequent reads
Grows linearly with the number of users
{1:N} ratio of users to artists, songs, genres etc.
DB size > 500gb => Should we shard?

24. Standalone Architecture
User activity
store

25. Sharding criteria
Should we shard?
• Indexes could no longer fit in memory.
What’s a good shard key?
• Uniformly distributed
• Hash based on day of registration is a
bad shard key
• Random device id can work
How do we migrate 500+ gb of data to
a shard?
• Pre-shard

26. 26
Tools

27. Cloud manager
Great for monitoring, backups and
upgrades.
Easy to setup and works with Slack.
Good at managing restarts.
Adding new machines into the cluster or
transitioning to xfs is not straight
forward.
https://www.mongodb.com/cloud

28. mTools
Excellent suite of tools to debug
performance issues
Helps detect and fix bottlenecks
Set up cronjobs to use mloginfo and
mplotqueries on a regular basis.
https://github.com/rueckstiess/mtools

29. Anticipate behavior - the best products can “mind read” aka Saavn A.I.
Intermediate ML models in MongoDB
Move frequently accessed map/reduce data to mongo
29
What’s next?

30. Thank you!
@eagleshack