03,04,05 Availability vs. Consistency; CAP Theorem; Consistency Patterns; Availability Patterns.

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Questions and Answers

What does the CAP theorem state about distributed computer systems?

They are designed to operate without any network failures.

They can sacrifice consistency for higher availability in all situations.

They can only support two out of the three guarantees at any time. (correct)

They can fully achieve consistency, availability, and partition tolerance.

In a CP system, what condition may result from waiting for a response from a partitioned node?

Data corruption due to synchronization issues.

Immediate availability of the most recent data.

A timeout error while waiting for a response. (correct)

Loss of all previous write operations.

What is a feature of an AP system?

It eliminates the impact of network failures on the system's performance.

It allows responses to be returned even when some nodes are unreachable. (correct)

It guarantees the most recent version of the data during all requests.

It prioritizes immediate consistency over system availability.

When should a distributed computer system favor partition tolerance?

When the system needs to operate despite network failures. Signup and view all the answers

What is a potential drawback of an AP system during a network partition?

The most recent data may not be included in responses. Signup and view all the answers

What is one characteristic of weak consistency?

Reads may not reflect recent writes immediately. Signup and view all the answers

In which scenario does eventual consistency operate effectively?

VoIP calls during intermittent connectivity. Signup and view all the answers

Which type of consistency guarantees that after a write, the most recent data is always read?

Strong consistency. Signup and view all the answers

Which of the following systems typically uses strong consistency?

Relational Database Management Systems (RDBMS). Signup and view all the answers

What mechanism does eventual consistency employ for data updates?

Asynchronous replication of writes. Signup and view all the answers

What happens during an active-passive fail-over if the heartbeat is interrupted?

The passive server takes over the active's IP address and resumes service. Signup and view all the answers

What is a key characteristic of active-active fail-over?

Both servers manage traffic and share the load. Signup and view all the answers

What is a potential disadvantage of implementing a fail-over system?

Higher costs due to additional hardware and complexity. Signup and view all the answers

How is availability typically quantified in IT systems?

As a percentage of uptime or downtime, often represented by 'nines'. Signup and view all the answers

In the context of database replication, what is the difference between master-slave and master-master configurations?

Master-slave allows only one master server to handle writes, while master-master allows both servers to handle writes. Signup and view all the answers

What is the acceptable downtime per year for a service with 99.99% availability?

52min 35.7s Signup and view all the answers

If two components each have 99.9% availability and are configured in sequence, what is their overall availability?

99.8% Signup and view all the answers

What is the downtime per day for a service that has 99.9% availability?

1m 26.4s Signup and view all the answers

How does availability change when components are configured in parallel?

Availability increases. Signup and view all the answers

What is the acceptable downtime per month for a service with 99.99% availability?

4m 23s Signup and view all the answers

Study Notes

CAP Theorem

A distributed computer system can only support two of three guarantees:
- Consistency: Every read receives the most recent write or an error.
- Availability: Every request receives a response, without guarantee it contains the most recent data.
- Partition Tolerance: The system continues to operate despite network failures.

Tradeoffs

Networks are unreliable, therefore partition tolerance is essential.
A choice must be made between consistency and availability.

CP (Consistency and Partition Tolerance)

Waiting for a response from a partitioned node might lead to timeouts.
This is suitable when atomic reads/writes are crucial for the business.

AP (Availability and Partition Tolerance)

Responses return the most readily available data from any node; it might not be the latest.
Writes may take time to propagate after partition resolution.
Suitable for eventual consistency or when the system must continue operating despite errors.

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Description

Explore the fundamentals of the CAP Theorem as it applies to distributed computer systems. Understand the trade-offs between consistency, availability, and partition tolerance, and the implications for system design. This quiz will enhance your knowledge of these essential concepts.