Design (LLD) NoSQL database - Machine Coding

Features Required:

1. Data Storage: The NoSQL database should support storing and retrieving large amounts of unstructured or semi-structured data, such as key-value pairs, documents, graphs, or time-series data.

2. Scalability: The database should be designed to scale horizontally, allowing for the addition of more machines/nodes to handle increased data storage and traffic.

3. High Availability: The database should ensure high availability by replicating data across multiple nodes, providing fault tolerance and automatic failover.

4. Query Language/Interface: The database should provide a query language or interface that allows users to efficiently retrieve and manipulate data.

5. Indexing: The database should support indexing mechanisms to enable faster searching and retrieval of data.

6. Data Consistency: The database should offer options for managing data consistency, such as eventual consistency, strong consistency, or consistency levels based on user requirements.

7. Security: The database should provide mechanisms for authentication, authorization, and encryption to ensure data security and privacy.

8. Backup and Recovery: The database should support backup and recovery mechanisms to prevent data loss and facilitate disaster recovery.

Design Patterns Involved or Used:

1. Replication: Replication is a key pattern used in NoSQL databases to ensure high availability and fault tolerance. It involves replicating data across multiple nodes to maintain multiple copies of the data.

2. Sharding: Sharding is a technique used to horizontally partition data across multiple machines. It allows for distributing the data and workload evenly to achieve scalability.

3. Observer Pattern: The observer pattern can be used to notify clients or applications about changes or events in the database. This allows for real-time notifications and synchronization of data.

4. Factory Pattern: The factory pattern can be used to create different types of database objects, such as connections, documents, or indexes, based on user requests.

Code: All Classes Created Based on Mentioned Patterns

// Database Interface
interface Database {
    void connect();
    void disconnect();
    void storeData(String key, Object value);
    Object retrieveData(String key);
}

// NoSQL Database Implementation
class NoSQLDatabase implements Database {
    private String host;
    private int port;
    private boolean isConnected;

    public NoSQLDatabase(String host, int port) {
        this.host = host;
        this.port = port;
        this.isConnected = false;
    }

    @Override
    public void connect() {
        System.out.println("Connected to NoSQL database: " + host + ":" + port);
        isConnected = true;
    }

    @Override
    public void disconnect() {
        System.out.println("Disconnected from NoSQL database: " + host + ":" + port);
        isConnected = false;
    }

    @Override
    public void storeData(String key, Object value) {
        if (isConnected) {
            System.out.println("Storing data in NoSQL database: " + key + " -> " + value);
            // Store the data in the NoSQL database
        } else {
            System.out.println("Cannot store data. Not connected to the database.");
        }
    }

    @Override
    public Object retrieveData(String key) {
        if (isConnected) {
            System.out.println("Retrieving data from NoSQL database for key: " + key);
            // Retrieve the data from the NoSQL database
            return null; // Placeholder for the retrieved data
        } else {
            System.out.println("Cannot retrieve data. Not connected to the database.");
            return null;
        }
    }
}

// Database Factory
class DatabaseFactory {
    public static Database createDatabase(String databaseType, String host, int port) {
        if (databaseType.equalsIgnoreCase("nosql")) {
            return new NoSQLDatabase(host, port);
        }
        // Handle other database types if needed
        return null;
    }
}

// Main Class
public class NoSQLDatabaseDesign {
    public static void main(String[] args) {
        String databaseType = "nosql";
        String host = "localhost";
        int port = 27017;

        Database database = DatabaseFactory.createDatabase(databaseType, host, port);
        database.connect();

        String key = "key1";
        Object value = "value1";
        database.storeData(key, value);

        Object retrievedValue = database.retrieveData(key);
        System.out.println("Retrieved value: " + retrievedValue);

        database.disconnect();
    }
}

In the above code, the Database interface provides the common methods required for a database, such as connecting, disconnecting, storing data, and retrieving data. The NoSQLDatabase class implements the Database interface and represents the implementation of a NoSQL database. The DatabaseFactory class acts as a factory to create the appropriate database object based on the database type specified.

The code demonstrates the usage of the factory pattern to create a NoSQL database object and perform basic database operations such as connecting, storing data, and retrieving data.

Please note that this is a simplified example, and a complete implementation of a NoSQL database involves more complex components, such as indexing, replication, and query processing.