1. Search data store for the world's largest
biometric identity system
Regunath Balasubramanian Shashikant Soni
regunathb@gmail.com soni.shashikant@gmail.com
twitter @regunathb
CONFIDENTIAL: For limited circulation only Slide 1

2. India
● 1.2 billion residents
● 640,000 villages, ~60% lives under $2/day
● ~75% literacy, <3% pays Income Tax, <20% banking
● ~800 million mobile, ~200-300 mn migrant workers
● Govt. spends about $25-40B on direct subsidies
● Residents have no standard identity document
● Most programs plagued with ghost and multiple identities causing
leakage of 30-40%
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3. Aadhaar
● Create a common ‘national identity’ for every ‘resident’
●Biometric backed identity to eliminate duplicates
●‘Verifiable online identity’ for portability
● Applications ecosystem using open APIs
●Aadhaar enabled bank account and payment platform
●Aadhaar enabled electronic, paperless KYC (Know Your
Customer)
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4. Search Requirements
● Multi-attribute query like:
name contains ‘regunath’ AND city = ‘bangalore’ AND
address contains ‘J P Nagar’ AND YearOfBirth = ……
● Search 1.2B resident data with photo, history
●35Kb - Average record size
● Response times in milliseconds
● Open scale out
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5. Why MongoDB
● Auto-sharding
● Replication
● Failover
… Essentially an AP (slaveOk) data store in CAP parlance
● Evolving schema
● Map-Reduce for analysis
● Full text search
●Compound (or) multi-keys
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6. Design
{ _id:123456789, name: ‘abcde’, year:1980, ….. }
MongoDB 2
Search API Client App
Name=‘abcde’
Solr 1
Address=‘some place’
Indexes Name: ‘abcde’ Year= 1980
Address: ‘some place’
year: 1980
● Read/Search
●Sharded Solr indexes for search
●Keyed document read from MongoDB
● Write
●Eventual consistency (across data sources) driven by
application
●Composite MongodDB-Solr app persistence handler Slide 6

7. Implementation and Deployment
● Start - 4M records in 2 shards
Current - 250M records in 8 shards ( 8 x ~2 TB x 3 replicas)
● Performance , Reliability & Durability
●SlaveOk
●getLastError, Write Concern: availability vs durability
 j = journaling
 w = nodes-to-write
● Replica-sets / Shards – how?
RS 1 RS 1 RS 1
Rs 2 RS 2 RS 2
Primary
Config 1 Config 2 Config 3
Secondary
Arbiter Router Router Router
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8. Monitoring and Troubleshooting
● Monitoring tools evaluated
●MMS
●munin
● Manual approach - daily ritual
●RS, DB, config, router - health and stats
● Problem analysis stats
●mongostat, iostat, currentOps, logs
●Client connections
● Stats for storage, shards addition
●Data file size
●Shard data distribution
●Replication
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9. Key Learnings on MongoDB
● Indexing 32 fields
●Compound indexes
●Multi-keys indexes
 {…"indexes" : [{ "email":"john.doe@email.com", "phone":"123456789“ }] }
 db.coll.find ({ "indexes.email" : "john.doe@email.com" })
●Indexes use b-tree
●Many fields to index
●Performs well upto 1-2M documents
●Best if index fits in memory
● Data replication, RS failover
●Rollback when RS goes out of sync
 Manual restore (physical data copy)
 Restarting a very stale node
Slide 9

10. Questions?
Regunath Balasubramanian Shashikant Soni
regunathb@gmail.com soni.shashikant@gmail.com
twitter @regunathb
CONFIDENTIAL: For limited circulation only Slide 10