This presentation by Maksym Voroniy (Consultant, Engineering, Kharkiv) was delivered at GlobalLogic Kharkiv Java Conference 2019 on June 9, 2019. Maksym shed light on obscure corners of distributed systems so that the audience clearly understood how the majority of well-known market products really function. Video: https://youtu.be/2Y7PDogSF4I

1. IGNORANCE OF CAP IS NOT AN
EXCUSE
why I ever should care about theory?

2. PREAMBLE
Complicated
business domain
Simple example
(book storage that
is CP)
Review of tool usage
(Distributed lock
pattern)
How to use it in real
project

3. MOTIVATION

4. CAP (IN BRIEF)
Availability
PartitioningConsistency
In distributed systems it is
impossible to implement atomic
read/write operation that
guarantees response to every
request
In the presence of a network
partition, one has to choose
between consistency and
availability.

5. AC EXAMPLE
from https://www.baltikon.lv/special/konsultant-buhgalter-flesh-versiya-va/
• classical RDBMS databases
• no concurrency
• no ability to scale

6. DID YOU JUST SAY “SCALE”?
Scalability is the property of a system to handle a
growing amount of work by adding resources to
the system (by Wiki)

7. AP EXAMPLE
AWS Cloud
Availability Zone 1
Auto Scaling group
Availability Zone 2
Auto Scaling group
Instance Instance
Instance Instance
Amazon EC2
Auto Scaling
private void handleInfiniteStream(InputStream is){
try {
var data = is.read();
// process data here
} catch (IOException e) {
log.error(e);
}
}
public void infiniteConsume(String connectionParam){
while (true) {
try (Connection conn = new Connection()) {
try(InputStream is = conn.inputStream()){
handleInfiniteStream(is);
}
} catch (IOException e) {
log.error(e); //retry connection
}
}
}

8. CP EXAMPLE
Master
Slave
db.products.insert(
{ item: "envelopes", qty : 100, type: "Clasp" },
{ writeConcern: { w: "majority" , wtimeout: 5000 }
} )
from https://docs.mongodb.com/manual/core/replica-set-write-concern/

9. CAP IS NEGATIVE
WE CAN USE IT
• Business driven solutions
• Relaxed requirements

10. IMROOVE “C” IN AP (KAFKA)
https://channel9.msdn.com/Shows/Azure-Friday/Introducing-Apache-Kafka-on-Azure-HDInsight https://bravenewgeek.com/tag/leader-election/
ZooKeeper allows implement leader election
algorithm by short time blocking
ISR = in-sync replicas

11. IMPROVE “A” FOR CP
Eventually (relaxed)
consistence
Partitioning still works
(master-master schema):
odd even
{id:1, name:’A’}, {id:2, name:’B’}
Use precise locking
• one lock per pack file.
• ...
• one lock for each
reference name.
• one lock for the index.

12. CONCLUSION
• CAP is everywhere
• CAP is negative so find your way out
• Speak with business if some requirements may be relaxed
Thank you!
maksym.voroniy@globallogic.com