Isolation levels are an essential concept in database management systems, ensuring data consistency and integrity during concurrent transactions. PostgreSQL, known for its robustness and compliance with the SQL standard, implements isolation levels using Multiversion Concurrency Control (MVCC). In this blog, we will explore the four standard isolation levels, their characteristics, and practical examples in PostgreSQL.

What Are Isolation Levels?

Isolation levels define the degree to which the operations in one transaction are isolated from those in other concurrent transactions. They help manage phenomena such as:

Introduction to Database Normalization: 1NF, 2NF, 3NF, and Beyond

Database normalization is a crucial concept in database design that aims to reduce data redundancy and ensure data integrity. The goal is to structure data in a way that makes it easier to manage and update, while maintaining its consistency. In this post, we’ll explore the most commonly used normal forms: 1NF, 2NF, and 3NF, and briefly mention other advanced normal forms (xxNF).

Understanding Idempotence in Computer Science

Idempotence is a key concept in computer science, especially in distributed systems, APIs, and web development. It ensures that repeating an operation multiple times results in the same outcome as performing it once. This property helps to maintain consistency, reliability, and fault tolerance in various systems, particularly when dealing with retries due to network failures or server errors.

In this blog, we’ll explore idempotence in different contexts and how it is used in practical scenarios.

1. Types

1.1 Common Errors and Pitfalls

Numeric Overflow

• Cause: Exceeding the range of a numeric type.
• Example:

  byte b = 127;
  b++; // Wraps to -128
  

Uninitialized Variables

• Cause: Using a local variable without initializing it.
• Example:

  int x;
  System.out.println(x); // Compilation Error
  

Missing Type Parameters

• Cause: Not specifying type parameters in generics, leading to runtime issues.
• Example:

  List list = new ArrayList(); // Raw type, can cause ClassCastException
  list.add(123);
  String str = (String) list.get(0); // Fails at runtime
  

1.2 String

public class Test {
    public static void main(String[] args) {
        String s1 = "Hello";
        String s2 = "Hello";
        String s3 = new String("Hello");

        System.out.println(s1 == s2); // true
        System.out.println(s1 == s3); // false
    }
}

1. s1 == s2:
   • Both s1 and s2 reference the same string literal “Hello”, which is stored in the string pool.
   • Since both variables point to the same object in memory, s1 == s2 evaluates to true.
2. s1 == s3:
   • s3 is created with the new keyword, which creates a new object in memory, even though it has the same content as s1.
   • Since s1 and s3 refer to different objects, s1 == s3 evaluates to false.

1.3 Integer

Use equals to compare whether objects are logically equal - two numbers has the same value in this case.