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CAP Theorem

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The CAP Theorem is a fundamental concept in distributed computing. It states that in the presence of a network partition, a distributed system can guarantee only two out of the following three properties:

The Three Components

1. Consistency (C)
   Every read receives the most recent write or an error.
   Example: If a book’s location is updated in a library system, everyone querying the catalog should see the updated location immediately.

2. Availability (A)
   Every request receives a (non-error) response, but not necessarily the most recent data.
   Example: Like a convenience store that’s always open, even if they occasionally run out of your favorite snack.

3. Partition Tolerance (P)
   The system continues to function despite network failures or communication breakdowns.
   Example: A distributed team in different rooms that still works, even if their intercom fails.

What the CAP Theorem Means

You can only pick two out of three:

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Real-World Examples

CAP Theorem trade-offs can be seen in:

• Social Media Platforms – Favor availability and partition tolerance (AP)
• Financial Systems – Require consistency and partition tolerance (CP)
• IoT Networks – Often prioritize availability and partition tolerance (AP)
• eCommerce Platforms – Mix of AP and CP depending on the service
• Content Delivery Networks (CDNs) – Strongly AP-focused for high availability and responsiveness

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graph TD
    A[Consistency]
    B[Availability]
    C[Partition Tolerance]

    A -- CP System --> C
    B -- AP System --> C
    A -- CA System --> B

    subgraph CAP Triangle
        A
        B
        C
    end

This diagram shows that you can choose only two at a time:

• CP (Consistency + Partition Tolerance): e.g., traditional databases
• AP (Availability + Partition Tolerance): e.g., DNS, Cassandra
• CA is only theoretical in a distributed environment (it fails when partition occurs)

In distributed systems, network partitions are unavoidable. The CAP Theorem helps us choose which trade-off makes the most sense for our use case.

#cap #consistency #availability #partitiontolerant

1: blog.devtrovert.com

2: Factor-bytes.com

3: blog.bytebytego.comVer 5.5.3