Implementation of Eventual Consistency

Differences between Eventual Consistency and Strong Consistency

Imagine you have a system where you want to store some information (like names and ages) but this system is split across many computers (nodes) to handle a lot of users. Each node has a copy of this information, and they need to stay in sync (consistent) with each other.

With eventual consistency, we’re okay with the information being slightly different on each node for a short time, as long as eventually (after some time), they all have the same correct information.

Below is the code of Eventual Consistency

C++

#include <iostream>
#include <unordered_map>
#include <vector>
#include <thread>
#include <mutex>
#include <chrono>
 
using namespace std;
 
// Define a simple key-value store
unordered_map<string, string> kvStore;
 
// Mutex for thread safety
mutex mtx;
 
// Function to update a key-value pair
void updateKV(const string& key, const string& value) {
    // Simulate some time passing
    this_thread::sleep_for(chrono::milliseconds(100));
     
    // Acquire lock to update the key-value store
    lock_guard<mutex> lock(mtx);
    kvStore[key] = value;
}
 
// Function to retrieve a value for a given key
string getKV(const string& key) {
    // Simulate some time passing
    this_thread::sleep_for(chrono::milliseconds(50));
     
    // Acquire lock to read from the key-value store
    lock_guard<mutex> lock(mtx);
    if (kvStore.find(key) != kvStore.end()) {
        return kvStore[key];
    }
    return "";
}
 
int main() {
    // Initialize the key-value store
    kvStore["name"] = "Alice";
    kvStore["age"] = "30";
     
    // Simulate concurrent updates
    vector<thread> threads;
    threads.emplace_back(updateKV, "name", "Bob");
    threads.emplace_back(updateKV, "age", "35");
 
    // Simulate concurrent reads
    threads.emplace_back([]() { cout << "Name: " << getKV("name") << endl; });
    threads.emplace_back([]() { cout << "Age: " << getKV("age") << endl; });
 
    // Wait for all threads to finish
    for (auto& t : threads) {
        t.join();
    }
 
    // Output the final state of the key-value store
    cout << "Final state:" << endl;
    for (auto it = kvStore.begin(); it != kvStore.end(); ++it) {
        cout << it->first << ": " << it->second << endl;
    }
 
    return 0;
}

Below is the explanation of above code:

Define Global Variables:
- kvStore: An unordered map used as a key-value store to store string key-value pairs.
- mtx: A mutex used for thread safety to protect concurrent access to kvStore.

updateKV Function:
- Simulates an update operation by updating a key-value pair in kvStore with a delay of 100 milliseconds.
- Acquires a lock on the mtx mutex before updating to ensure only one thread can update the store at a time.
getKV Function:
- Simulates a read operation by reading a key-value pair from kvStore with a delay of 50 milliseconds.
- Acquires a lock on the mtx mutex before reading to ensure only one thread can read from the store at a time.
Main Function:
- Initializes the key-value store kvStore with some initial values.
- Creates threads to simulate concurrent updates and reads to the store.
- Waits for all threads to finish using join().
- Outputs the final state of the key-value store.

Eventual Consistency in Distributed Systems | Learn System Design

Consistency in a distributed system refers to the property that the data stored on different nodes of the system is always in agreement with each other. In other words, all nodes in the system have the same view of the data at all times.

Important Topics for the Eventual Consistency in Distributed Systems

What is the Importance of Data Consistency?
What is Eventual Consistency?
Characteristics of Eventual Consistency
Real-Life Example of Eventual Consistency
How Eventual Consistency works?
Use-Cases of Eventual Consistency
Impact of Eventual Consistency on (System performance, Scalability, and Availability)
Differences between Eventual Consistency and Strong Consistency
Implementation of Eventual Consistency
Benefits of Eventual Consistency
Challenges of Eventual Consistency

Implementation of Eventual Consistency

Below is the code of Eventual Consistency

C++

Below is the explanation of above code:

Eventual Consistency in Distributed Systems | Learn System Design

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