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ZeeshanAli-0704

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Design A Paste Bin

Table of Contents

  1. Overview

  2. Requirements and Goals of the System

  3. Design Considerations

  4. Capacity Estimation and Constraints

  5. Storage and Bandwidth Estimates

  6. System APIs

  7. Database Design

  8. High Level Design

  9. Component Design

  10. Advanced Topics

The links above will take you to the respective sections within the document.

Designing a Pastebin Like Web Service

Overview

Pastebin is a service that allows users to store plain text and generate unique URLs for easy sharing. Users can paste text, which then gets stored on the server, and receive a URL through which others can access the content. Such services are often used for sharing code snippets, configurations, logs, or any plain text.

Similar Services: pastebin.com, pasted.co, chopapp.com

Difficulty Level: Easy

Requirements and Goals of the System

Functional Requirements:

  1. Paste Creation: Users should be able to paste their text and receive a unique URL for access.
  2. Text Only: The service will only support plain text.
  3. Expiration: Pastes will expire after a certain period, either default or user-specified.
  4. Custom Aliases: Users should be able to choose custom URLs for their pastes.

Non Functional Requirements:

  1. Reliability: The system must be reliable, ensuring no data loss.
  2. Availability: The service must be highly available, so users can always access their pastes.
  3. Low Latency: Users should be able to access their pastes quickly.
  4. Security: URLs should not be easily guessable or predictable.

Extended Requirements:

  1. Analytics: Track how often a paste is accessed.
  2. API Access: Provide REST APIs for third-party services to create, retrieve, or delete pastes.

Design Considerations

  • Text Size Limit: To prevent abuse, we can impose a maximum paste size of 10MB.
  • Custom URL Limits: Enforcing size limits on custom URLs ensures a consistent and manageable database.

Capacity Estimation and Constraints

The system is expected to be read-heavy, with more read requests than paste creation. A 5:1 ratio between read and write operations is assumed.

Traffic Estimates:

  • New Pastes: 1 million per day
  • Reads: 5 million per day

New Pastes per second:

1M X 24 X 3600  = 12 pastes/sec
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Paste Reads per second:

5M X 24 X 3600  = 58 reads/sec
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Storage Estimates:

  • Average Paste Size: 10KB
  • Daily Storage: 1 million pastes × 10KB = 10GB/day

  • Yearly Storage: 10GB/day × 365 days ≈ 3.65TB/year

  • Storage for 10 Years: 3.65TB/year × 10 years = 36.5TB

Key Generation and Storage:

Storage and Bandwidth Estimates:

  • With 1 million pastes daily, there will be 3.6 billion pastes over 10 years.

Unique Key Generation and Storage:

  • Base64 Encoding: Six-letter strings using base64 encoding can generate about 68.7 billion unique strings.
  • Storage for Keys:

    3.6 billion pastes × 6 bytes = 22GB

  • Adjusted Storage Needs:

    To avoid full capacity, we add 30% more storage:
    36.5TB × 1.3 ≈ 47.45TB

Bandwidth Estimates:

  • Write Requests: 12 pastes per second

    • Ingress: 12 pastes × 10KB = 120KB/s
  • Read Requests: 58 reads per second

    • Egress: 58 reads × 10KB = 0.6MB/s

Memory Estimates:

To improve read performance, caching frequently accessed pastes is important. Assuming the 80-20 rule:

  • Cache Storage: 20% of 5 million pastes × 10KB = 10GB

System APIs

Create Paste API:

  • Endpoint: /createPaste
  • Method: POST
  • Parameters:
    • api_dev_key (string): Developer's API key.
    • paste_data (string): Textual data of the paste.
    • custom_url (string): Optional custom URL.
    • user_name (string): Optional username for URL generation.
    • paste_name (string): Optional name of the paste.
    • expire_date (string): Optional expiration date.
  • Returns: A URL for accessing the paste or an error code.

Retrieve Paste API:

  • Endpoint: /retrievePaste
  • Method: GET
  • Parameters:
    • api_paste_key (string): The unique key for the paste.
  • Returns: The paste’s content or an error code.

Delete Paste API:

  • Endpoint: /deletePaste
  • Method: DELETE
  • Parameters:
    • api_paste_key (string): The unique key for the paste.
  • Returns: true for success, false for failure.

Database Design

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Database Schema:

  1. Pastes Table:

    • URLHash: Unique hash for the URL.
    • ContentKey: Key pointing to the paste's content.
    • CreationDate: Timestamp of creation.
    • ExpirationDate: Timestamp when the paste should expire.
    • UserName: (Optional) Username associated with the paste.
  2. Users Table:

    • UserID: Unique identifier for the user.
    • UserName: Username chosen by the user.
    • Pastes: List of pastes created by the user.

High Level Design

The system consists of an application layer and a datastore layer:

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  1. Application Layer: Handles read/write requests and communicates with the datastore. It also handles key generation, either dynamically or through a Key Generation Service (KGS).

  2. Datastore Layer:

    • Metadata Storage: Stores paste metadata (e.g., URLHash, ContentKey) in a relational or distributed key-value store.
    • Object Storage: Stores the actual content, such as Amazon S3.

Key Generation Service (KGS):

A dedicated service generates unique keys and stores them in a key-DB, preventing key duplication.

Please refer design-a-url-shortner-tiny-url

Caching:

A cache layer stores frequently accessed pastes to reduce latency and load on the database.

Component Design

Write Requests:

  1. Key Generation: Generate a random six-letter key.
  2. Database Insertion: Store the paste content and associated metadata in the database.
  3. Handle Duplicates: If a key collision occurs, regenerate the key and retry.

Read Requests:

  1. Retrieve Paste: Query the datastore using the paste key.
  2. Return Content: Return the content if found; otherwise, return an error.

Advanced Topics

Data Partitioning and Replication:

Data partitioning can be based on key hashing, and replication ensures high availability and fault tolerance.

Purging and Cleanup:

Expired pastes should be purged regularly to free up storage. A background service can handle this.

Cache and Load Balancer:

A caching layer reduces database load by storing frequently accessed pastes. A load balancer distributes incoming requests across application servers.

Security and Permissions:

  • Access Control: Secure the API with developer keys and OAuth tokens.
  • Encryption: Use HTTPS for all communications to prevent data breaches.
  • Rate Limiting: Implement rate limiting to prevent abuse.

This detailed design outlines the architecture and operational considerations for building a scalable, reliable, and performant Pastebin-like service.

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