This document discusses using Node.js and Cassandra for highly concurrent systems. It explains that Node.js is well-suited for I/O-bound applications with low CPU usage that require high concurrency. This is because Node.js uses an event-driven, non-blocking model that handles connections efficiently in a single thread without much overhead. The document also introduces the Cassandra driver for Node.js, which features connection pooling, load balancing, retry functions, and row/field streaming for efficiently accessing Cassandra from Node.js applications. Examples are given showing how to perform queries, stream rows and fields to responses.

1. Node.js and Cassandra
For highly concurrent systems

2. Software as a service
Most common scenario
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I/O Bound
o db
o other services
o file system
Low CPU usage
Peaks and valleys

3. Why Node.js

4. Why Node.js
Event-based
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Single threaded
Minimum overhead per connection
Predictable amount of memory under load
Apache / IIS vs Nginx: Process-based vs event-loop
Everything runs in parallel except your code

5. Why Node.js
Event-based: Apache vs Nginx
source webfaction.com

6. Why Node.js
Async I/O
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Uses OS network interfaces + fixed thread pool
Time spent: db connections / files

7. Why Node.js
Javascript: Closures
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CPS: Continuation passing style
The scope of the outer function -> inner function
Javascript: Functional / Dynamic / Object oriented
... packet manager / os community / V8 / ubiquitous...

8. Why Node.js
Stream everything
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Avoid buffering
HTTP: Chunked requests and responses
TCP: Chunks readable in a stream
Stream Piping (UNIX like)

9. The Driver for Cassandra

10. The Driver for Cassandra
Features
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Connection pooling to multiple hosts
Load balancing
Automatic failover / retry
Row and field streaming
Queuing: Concurrent connecting / preparing

11. The Driver for Cassandra
App
Cassandra nodes
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G
E
D
C
F
H
B

12. The Driver for Cassandra
Sample: Json Web Api
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app.get('/user/:id', function (req, res, next){
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var query = 'SELECT * FROM users WHERE id = ?';
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cassandra.executeAsPrepared(query, [req.params.id], function (err, result) {
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if (err) return next(err);
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var row = result.rows[0];
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//Response: expose some properties of the user
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res.json({id: req.params.id, name: row.get('name')});
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});
});

13. The Driver for Cassandra
How row streaming works
Readable
stream
Transform
stream
Transform
stream
Socket
Protocol
Parser
Chunks
Heade
r and
body
chunk
s
Client
Row

14. The Driver for Cassandra
Sample: Field streaming
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app.get('/user/:id/image', function (req, res, next){
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var query = 'SELECT id, profile_image FROM users WHERE id = ?';
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cassandra.streamField(query, [req.params.id], function (err, row, image) {
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if (err) return next(err);
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//pipe the image stream to the response stream
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image.pipe(res);
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});
});

15. The Driver for Cassandra
Sample: Field streaming + image resizing
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app.get('/user/:id/image', function (req, res, next){
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var query = 'SELECT id, profile_image FROM users WHERE id = ?';
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cassandra.streamField(query, [req.params.id], function (err, row, image) {
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if (err) return next(err);
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//pipe the image stream to a resizer stream
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image.pipe(resizer).pipe(res);
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});
});

16. Moving forward
Next features
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Multiple data centers support.
Cassandra query tracing
Contribute! :)

17. Thanks!
Jorge Bay Gondra
@jorgebg
jorgebaygondra@gmail.com
github.com/jorgebay/node-cassandra-cql
npm install node-cassandra-cql

18. A Design Framework for Highly Concurrent Systems by Matt Welsh, Steven D. Gribble, Eric A.
Brewer, and David Culler @ UC Berkeley
Concurrency is not Parallelism (it's better) by Rob Pike @Google Go lang
How the single threaded non blocking IO model works in Node.js
References and further reading