Speaker: Aly Cabral Real-time feedback is an essential part of modern application development where developers want to sync across platforms, systems, and users to provide better end-user experiences. In MongoDB 3.6, change streams will empower developers to easily leverage the power of MongoDB's internal real-time functionality to react to relevant data changes immediately. This session introduces change streams and walks you through developing against them. We will dive into use cases and explore how to make good architectural decisions around this new functionality.

1. # M D B l o c a l
Aly Cabral, Product Manager
Using Change Streams to
Keep Up With Your Data

2. # M D B l o c a l
Alyson Cabral
PRODUCT MANAGER | MONGODB | @ ALY_CABRAL

3. # M D B l o c a l
“TIME IS MONEY.”
B E N J A M I N F R A N K L I N
WA R R E N B U F F E T

4. # M D B l o c a l
REAL-TIME IS AN EXPECTATION
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5. # M D B l o c a l
MongoDB
Action
Handler
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6. # M D B l o c a l
const changeStream=
db.collection(‘temperature’).watch();
c h a n g e S t r e a m . o n ( ' c h a n g e ' , f u n c t i o n ( c h a n g e ) {
c o n s o l e . l o g ( c h a n g e ) ;
} ) ;
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7. # M D B l o c a l
CHANGE STREAM
CHARACTERISTICS

8. # M D B l o c a l
5 OPERATION TYPES
INSERT
DELETE
REPLACE
UPDATE
INVALIDATE
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9. # M D B l o c a l
CHANGE STREAMS UTILIZE
COLLECTION ACCESS CONTROLS,
PRESENT A DEFINED API, AND ENABLE
SCALING ACROSS PRIMARIES AND
SECONDARIES.
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10. # M D B l o c a l
TOTAL ORDERING OF CHANGES ACROSS
SHARDS
mongos
3 1
2
Shard 1 Shard 2 Shard 3
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11. # M D B l o c a l
PS
CHANGES ARE DURABLE
P
S
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12. # M D B l o c a l
SP
CHANGE STREAMS ARE RESUMABLE
P
S
{_id: <resumeToken>,
operationType: ‘update’,
ns: {db: ‘data’, coll: ‘temperature’},
documentKey: {_id: ‘room12345’},
updateDescription: {updatedFields: {temperature: 70},
removedFields: [‘humidity’]}
}
var newChangeStream = coll.watch({ resumeAfter: <cachedResumeToken> });
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13. # M D B l o c a l
CHANGE STREAMS UTILIZE THE POWER
OF THE AGGREGATION FRAMEWORK
$match $project $addFields $replaceRoot $redact
var changeStream = coll.watch([{ $match: {$or: [{operationType: 'delete' }, {operationType:'replace'}]}}]);
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14. # M D B l o c a l
1. COLLECTION ACCESS CONTROLS
2. DEFINED API
3. ENABLE SCALING
4. TOTAL ORDERING
5. DURABLE
6. RESUMABLE
7. POWER OF AGGREGATION
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15. # M D B l o c a l
OPERATION TYPES

16. # M D B l o c a l
5 OPERATION TYPES
{ _id: (resumeToken),
operationType: ‘insert’,
ns: {db: ‘test’, coll: ‘foo’},
documentKey: {userName: ‘alice123’,
_id: ObjectId("58a4eb4a30c75625e00d2820")
},
fullDocument: {_id: ObjectId("58a4eb4a30c75625e00d2820"),
userName: ‘alice123’,
name: ‘Alice’
}
}
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INSERT

17. # M D B l o c a l
5 OPERATION TYPES
{_id: (resumeToken),
operationType: ‘delete’,
ns: {db: ‘test’, coll: ‘foo’},
documentKey: {userName: ‘alice123’,
_id: ObjectId("58a4eb4a30c75625e00d2820")
}
}
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DELETE

18. # M D B l o c a l
5 OPERATION
TYPES
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{_id: (resumeToken),
operationType: ‘replace’,
ns: {db: ‘test’, coll: ‘foo’},
documentKey: {userName: ‘alice123’,
_id: ObjectId("58a4eb4a30c75625e00d2820")
},
fullDocument: {_id: ObjectId("58a4eb4a30c75625e00d2820"),
userName: ‘alice123’,
name: ‘Alice’
}
}
REPLACE

19. # M D B l o c a l
UPDATE5 OPERATION TYPES
@ A LY_C A B R A L
{_id: (resumeToken),
operationType: ‘update’,
ns: {db: ‘test’, coll: ‘foo’},
documentKey: {userName: ‘alice123’,
_id: ObjectId("58a4eb4a30c75625e00d2820")
},
updateDescription: {updatedFields: {email: ‘alice@10gen.com’},
removedFields: [‘phoneNumber’]}
}

20. # M D B l o c a l
5 OPERATION
TYPES
{_id: (resumeToken),
operationType: ‘invalidate’,
ns: {db: ‘test’, coll: ‘foo’}}
@ A LY_C A B R A L
INVALIDATE

21. # M D B l o c a l
{_id: (resumeToken),
operationType: ‘update’,
ns: {db: ‘test’, coll: ‘foo’},
documentKey: {userName: ‘alice123’,
_id: ObjectId("58a4eb4a30c75625e00d2820")},
updateDescription: {updatedFields: {email: ‘alice@10gen.com’},
removedFields: [‘phoneNumber’]}
}
UPDATE
var changeStream = coll.watch({ fullDocument: 'updateLookup' });
@ A LY_C A B R A L

22. # M D B l o c a l
var changeStream = coll.watch({ fullDocument: 'updateLookup' });
UPDATE fullDocument: updateLookup
{_id: (resumeToken),
operationType: ‘update’,
ns: {db: ‘test’, coll: ‘foo’},
documentKey: {userName: ‘alice123’,
_id: ObjectId("58a4eb4a30c75625e00d2820")},
updateDescription: {updatedFields: {email:
‘alice@10gen.com’},
removedFields: [‘phoneNumber’]},
fullDocument: { _id: ObjectId("58a4eb4a30c75625e00d2820"),
name: ‘Alice’,
userName: ‘alice123’,
email: ‘alice@10gen.com’,
team: ‘replication’}
}
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23. # M D B l o c a l
1 . S H A R D K E Y I S U S E D ( B Y T H E M O N G O S ) TO R O U T E
O P E R AT I O N S
2 . _ I D U N I Q U E N E S S I S E N F O R C E D B Y S H A R D
mongos
3 1
2
Shard 1 Shard 2 Shard 3
DEFINING THE documentKey
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24. # M D B l o c a l
BACK TO
THE USE CASE

25. # M D B l o c a l@ A LY_C A B R A L

26. # M D B l o c a l
Action Handler
{_id: (resumeToken),
operationType: ‘insert’,
ns: {db: ‘data’, coll: ‘temperature’},
documentKey: {_id: ‘greenRoom123’},
fullDocument: {_id: ‘greenRoom123’),
temperature: 75,
username: aly_cabral}
}
var changeStream = coll.watch([{
$match: {{ 'fullDocument.temperature': {$gte : 70 }}},
{fullDocument: 'updateLookup' }]);
@ A LY_C A B R A L

27. # M D B l o c a l
{_id: (resumeToken),
operationType: ‘insert’,
ns: {db: ‘data’, coll: ‘temperature’},
documentKey: {_id: ‘orangeRoom123’
fullDocument: {_id: ‘orangeRoom123’,
temperature: 76,
username: eliot_horowitz }
}
Action Handler
var changeStream = coll.watch([{
$match: {{ 'fullDocument.temperature': {$gte : 70 }}},
{fullDocument: 'updateLookup' }]);
temperature: 75
username: aly_cabral
@ A LY_C A B R A L

28. # M D B l o c a l
Action Handler
{_id: (resumeToken),
operationType: ‘update’,
ns: {db: ‘data’, coll: ‘temperature’},
documentKey: {_id: ‘greenRoom123’)},
updateDescription: {updatedFields: {temperature: 68}
fullDocument: {_id: ‘greenRoom123’,
temperature: 68,
username: aly_cabral}
}
var changeStream = coll.watch([{
$match: {{ 'fullDocument.temperature': {$gte : 70 }}},
{fullDocument: 'updateLookup' }]);
temperature: 75
username: aly_cabral
@ A LY_C A B R A L

29. # M D B l o c a l
IF YOUR APPLICATION REQUIRES STATE
ALWAYS MATCH ON UNCHANGING
FIELDS
@ A LY_C A B R A L

30. # M D B l o c a l
Action Handler
var changeStream = coll.watch([{ $match: {{ 'fullDocument.username': ‘aly_cabral’ }}},
{fullDocument: 'updateLookup' }]);
temperature: 75
username: aly_cabral
{_id: (resumeToken),
operationType: ‘insert’,
ns: {db: ‘data’, coll: ‘temperature’},
documentKey: {_id: ‘blueRoom123’},
fullDocument: {_id: ‘blueRoom123’,
temperature: 85,
username: aly_cabral}
}
@ A LY_C A B R A L

31. # M D B l o c a l
Action Handler
var changeStream = coll.watch([{ $match: {{ 'fullDocument.username': ‘aly_cabral’ }}},
{fullDocument: 'updateLookup' }]);
temperature: 75
username: aly_cabral
temperature: 85
username: aly_cabral
{_id: (resumeToken),
operationType: ‘delete’,
ns: {db: ‘data’, coll: ‘temperature’},
documentKey: {_id: ‘blueRoom123’}}
@ A LY_C A B R A L

32. # M D B l o c a l
Action Handler
{_id: (resumeToken),
operationType: ‘replace’,
ns: {db: ‘data’, coll: ‘temperature’},
documentKey: {_id: ‘blueRoom123’},
fullDocument: {_id: ‘blueRoom123’,
temperature: 71,
username: asya_kamsky}
}
var changeStream = coll.watch([{ $match: {{ 'fullDocument.username': ‘aly_cabral’ }}},
{fullDocument: 'updateLookup' }]);
temperature: 75
username: aly_cabral
temperature: 85
username: aly_cabral
@ A LY_C A B R A L

33. # M D B l o c a l
IF YOUR APPLICATION NEEDS TO NOTIFY ON DELETED
DATA
ALWAYS HANDLE DELETES AND
REPLACES APPROPRIATELY
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34. # M D B l o c a l
var changeStream = coll.watch([{ $match: {
{ $or: [ { 'fullDocument.username': ‘aly_cabral'
}, { operationType: 'delete' },
{ operationType: 'replace' }]}],
{fullDocument: 'updateLookup' });
Insert
@ A LY_C A B R A L

35. # M D B l o c a l
var changeStream = coll.watch([{ $match: {
{ $or: [ { 'fullDocument.username': ‘aly_cabral'
}, { operationType: 'delete' },
{ operationType: 'replace' }]}],
{fullDocument: 'updateLookup' });
Insert Update
@ A LY_C A B R A L

36. # M D B l o c a l
var changeStream = coll.watch([{ $match: {
{ $or: [ { 'fullDocument.username': ‘aly_cabral'
}, { operationType: 'delete' },
{ operationType: 'replace' }]}],
{fullDocument: 'updateLookup' });
Insert Update Delete
@ A LY_C A B R A L

37. # M D B l o c a l
var changeStream = coll.watch([{ $match: {
{ $or: [ { 'fullDocument.username': ‘aly_cabral'
}, { operationType: 'delete' },
{ operationType: 'replace' }]}],
{fullDocument: 'updateLookup' });
Insert Update Delete
In the update notification fullDocument: null
updateLookup
@ A LY_C A B R A L

38. # M D B l o c a l
var changeStream = coll.watch([{ $match: {
{ $or: [ { 'fullDocument.username': ‘aly_cabral'
}, { operationType: 'delete' },
{ operationType: 'replace' }]}],
{fullDocument: 'updateLookup' });
Insert Update Delete
In the update notification fullDocument: null
updateLookup
{_id: (resumeToken),
operationType: ‘update’,
ns: {db: ‘data’, coll: ‘temperature’},
documentKey: {userName: ‘greenRoom123’},
updateDescription: {updatedFields: {temperature: 78}},
fullDocument: {}
}
@ A LY_C A B R A L

39. # M D B l o c a l
IF YOU NEED TO SEE EVERY CHANGE (EVEN OUTDATED
CHANGES) TO A DOCUMENT
HAVE MATCHING FIELDS IN THE
DOCUMENT KEY
@ A LY_C A B R A L

40. # M D B l o c a l
{_id: (resumeToken),
operationType: ‘insert’,
ns: {db: ‘data’, coll: ‘temperature’},
documentKey: {_id: ‘blueRoom123’,
username: “aly_cabral”},
fullDocument: {_id: ‘blueRoom123’,
temperature: 85,
username: “aly_cabral”}
}
Action Handler
var changeStream = coll.watch([{ $match: {{ ‘documentKey.username’: ‘aly_cabral’ }}},
{fullDocument: 'updateLookup' }]);
temperature: 75
username: aly_cabral
@ A LY_C A B R A L

41. # M D B l o c a l
Action Handler
var changeStream = coll.watch([{ $match: {{ ‘documentKey.username’: ‘aly_cabral’ }}},
{fullDocument: 'updateLookup' }]);
temperature: 75
username: aly_cabral
temperature: 85
username: aly_cabral
{_id: (resumeToken),
operationType: ‘delete’,
ns: {db: ‘data’, coll: ‘temperature’},
documentKey: {_id: ‘blueRoom123’,
username: “aly_cabral”)}}
@ A LY_C A B R A L

42. # M D B l o c a l
{_id: (resumeToken),
operationType: ‘insert’,
ns: {db: ‘data’, coll: ‘temperature’},
documentKey: {_id: ‘blueRoom123’,
username: “aly_cabral”},
fullDocument: {_id: ‘blueRoom123’,
temperature: 85,
username: “aly_cabral”}
}
Action Handler
var changeStream = coll.watch([{ $match: {{ ‘documentKey.username’: ‘aly_cabral’ }}},
{fullDocument: 'updateLookup' }]);
temperature: 75
username: aly_cabral
temperature: 85
username: aly_cabral
{_id: (resumeToken),
operationType: ‘delete’,
ns: {db: ‘data’, coll: ‘temperature’},
documentKey: {_id: ‘blueRoom123’,
username: “aly_cabral”)}}
{_id: (resumeToken),
operationType: ‘replace’,
ns: {db: ‘data’, coll: ‘temperature’},
documentKey: {_id: ‘greenRoom123’,
username: ‘aly_cabral’},
fullDocument: {_id: ‘greenRoom123’,
temperature: 71,
username: “asya_kamsky”}
}
@ A LY_C A B R A L

43. # M D B l o c a l
UNDERLYING
TECHNOLOGY

44. # M D B l o c a l
P
S
S
S
S
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45. # M D B l o c a l
123456
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46. # M D B l o c a l
RESUMABLE
304 270 233 208 201 190
C A C H E D R E S U M E TO K E N : 2 0 8
N E W E S T O L D E S T
D E L E T E D
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47. # M D B l o c a l
304 270 233 208 201 190
C A C H E D R E S U M E TO K E N : 1 9 0
N E W E S T O L D E S T
D E L E T E D
NON-RESUMABLE
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48. # M D B l o c a l
YOU MADE IT!
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