Linked Lists: Powering Data Engineering Workflows 

Data engineers juggle a diverse arsenal of data structures to manage ever-growing data volumes and complex formats. Among these tools, Linked Lists emerge as a powerful weapon, offering flexibility and dynamism. This blog post delves into the core concepts of Linked Lists, explores their applications in data engineering, particularly within Extract, Transform, Load (ETL) pipelines, and demonstrates how they empower efficient and scalable data processing solutions. 

Understanding Linked Lists: Building Blocks for Flexibility

Imagine a train with connected cars. Each car (node) carries valuable data and is linked to the next car (reference) in the sequence. This analogy captures the essence of a Linked List: a dynamic data structure where elements (nodes) are not stored contiguously in memory but rather connected through references. This flexibility offers distinct advantages:

Dynamic Sizing: Unlike arrays, Linked Lists don't require pre-allocation of memory. You can add or remove nodes on the fly, making them ideal for scenarios where data size is unpredictable.

Efficient Insertion/Removal: Inserting or removing elements at any position becomes a breeze as you only need to manipulate the references between nodes. This is a stark contrast to arrays, where insertion or removal in the middle can involve significant data shifting.

Types of Linked Lists

Linked lists are fundamental data structures that store elements in a linear fashion. Unlike arrays, elements in a linked list are not stored contiguously in memory. Instead, each element (node) holds data and a reference (pointer) to the next node in the sequence. This dynamic allocation allows for efficient insertions and deletions at any point in the list.

There are two main types of linked lists, each offering distinct advantages:

Code Example: A Glimpse into Single Linked Lists (Java)

To solidify our understanding, let's explore a basic single linked list implementation in Java:

class Node {

  int data;

  Node next;


  public Node(int data) {

    this.data = data;

  }

}


public class SingleLinkedList {

  private Node head;


  public void addFirst(int data) {

    Node newNode = new Node(data);

    newNode.next = head;

    head = newNode;

  }


  public void printList() {

    Node current = head;

    while (current != null) {

      System.out.print(current.data + " -> ");

      current = current.next;

    }

    System.out.println("NULL");

  }


  public static void main(String[] args) {

    SingleLinkedList list = new SingleLinkedList();

    list.addFirst(5);

    list.addFirst(3);

    list.addFirst(1);

    list.printList(); // Output: 1 -> 3 -> 5 -> NULL

  }

}

This code demonstrates a single linked list where we can add elements at the beginning (addFirst) and traverse the list using a while loop until we encounter the null reference at the end.

Beyond Caching: Linked Lists in Action

While linked lists excel in handling collisions in caching and maintaining insertion order in hash sets/maps, their applications extend far beyond:

Linked Lists and DAGs: Orchestrating ETL Pipelines

Directed Acyclic Graphs (DAGs) are crucial for representing the dependencies between stages in ETL pipelines. Here's where linked lists come into play:

This approach ensures tasks are triggered in the correct order based on their dependencies.

Sources

I hope this provides a clear and concise explanation of linked lists, focusing on single and double linked lists!