--- title: "What is Latency in Software?" description: "What is Latency in Software?" author: "Anubhav Sharma" published: 2026-01-13 updated: 2026-01-13 canonical: https://www.mindstick.com/interview/34441/what-is-latency-in-software category: "software development" tags: ["developer"] reading_time: 5 minutes --- # What is Latency in Software? **Latency** in software refers to the **time delay** between a **request** being made and the **response** being received. In simple terms: > ## Latency = How long you wait before something starts happening ## ## Interview One-Liner > **Latency is the delay between sending a request and receiving a response in a software system.** ## Simple Example You click a **button** - The app responds **after 300 ms** - That **300 ms is latency** ## Formal Definition > **Latency is the total time taken for data to travel from source to destination and back, including processing delays.** ## Types of Latency in Software ### 1. Network Latency Time taken for data to travel over the network. ## Causes: - Physical distance - Number of hops (routers) - Congestion - DNS lookup time ## Example: API call taking 120 ms due to network delay ### 2. Application Latency Time spent inside the application. ## Causes: - Slow business logic - Blocking threads - Poor algorithms ## Example: Heavy loop or synchronous I/O ### 3. Database Latency Time taken to execute DB queries. ## Causes: - Missing indexes - Locking - Slow joins ## Example: SQL query taking 500 ms ### 4. Disk / I/O Latency Time to read/write from disk. ## Causes: - HDD vs SSD - File system overhead ## Example: File read delay ### 5. Rendering / UI Latency Time from data arrival to UI update. ## Example: - Slow DOM rendering - Heavy UI frameworks ## Latency vs Throughput (Important Difference) | Metric | Latency | Throughput | | --- | --- | --- | | Meaning | Delay per request | Requests per second | | Unit | ms, μs | req/sec | | Focus | Speed of response | Volume of work | > ## Low latency ≠ high throughput ## Real-World Analogy - **Latency** → Time taken for a car to reach destination - **Throughput** → Number of cars passing per hour ## Why Latency Matters - User experience (anything > 100ms feels slow) - Real-time systems (chat, trading) - Distributed systems - APIs and microservices ## Acceptable Latency (Rule of Thumb) | Latency | User Perception | | --- | --- | | < 100 ms | Instant | | 100–300 ms | Slight delay | | 300–1000 ms | Noticeable | | > 1 sec | Slow | | > 3 sec | Unusable | ## How to Reduce Latency ### Network - [Use CDN](https://www.mindstick.com/blog/305904/how-to-use-a-cdn-content-delivery-network-to-improve-site-speed) - Reduce round trips - Keep connections alive ### Application - [Async / non-blocking code](https://www.mindstick.com/interview/34235/what-is-the-async-and-await-pattern-in-c-sharp-when-should-you-use-it) - [Caching](https://www.mindstick.com/forum/161233/what-is-caching-and-why-is-it-used) - Efficient algorithms ### Database - [Indexing](https://www.mindstick.com/blog/303489/the-significance-of-indexing-in-databases-for-seo) - Query optimization - Read replicas ## Latency in Real-Time Systems - **WebSocket / SSE** → designed for low latency - **REST APIs** → higher latency per request - **Polling** → high latency & wasteful ## ## Answers ### Answer by Anubhav Sharma **Latency** in software refers to the **time delay** between a **request** being made and the **response** being received. In simple terms: > ## Latency = How long you wait before something starts happening ## ## Interview One-Liner > **Latency is the delay between sending a request and receiving a response in a software system.** ## Simple Example You click a **button** - The app responds **after 300 ms** - That **300 ms is latency** ## Formal Definition > **Latency is the total time taken for data to travel from source to destination and back, including processing delays.** ## Types of Latency in Software ### 1. Network Latency Time taken for data to travel over the network. ## Causes: - Physical distance - Number of hops (routers) - Congestion - DNS lookup time ## Example: API call taking 120 ms due to network delay ### 2. Application Latency Time spent inside the application. ## Causes: - Slow business logic - Blocking threads - Poor algorithms ## Example: Heavy loop or synchronous I/O ### 3. Database Latency Time taken to execute DB queries. ## Causes: - Missing indexes - Locking - Slow joins ## Example: SQL query taking 500 ms ### 4. Disk / I/O Latency Time to read/write from disk. ## Causes: - HDD vs SSD - File system overhead ## Example: File read delay ### 5. Rendering / UI Latency Time from data arrival to UI update. ## Example: - Slow DOM rendering - Heavy UI frameworks ## Latency vs Throughput (Important Difference) | Metric | Latency | Throughput | | --- | --- | --- | | Meaning | Delay per request | Requests per second | | Unit | ms, μs | req/sec | | Focus | Speed of response | Volume of work | > ## Low latency ≠ high throughput ## Real-World Analogy - **Latency** → Time taken for a car to reach destination - **Throughput** → Number of cars passing per hour ## Why Latency Matters - User experience (anything > 100ms feels slow) - Real-time systems (chat, trading) - Distributed systems - APIs and microservices ## Acceptable Latency (Rule of Thumb) | Latency | User Perception | | --- | --- | | < 100 ms | Instant | | 100–300 ms | Slight delay | | 300–1000 ms | Noticeable | | > 1 sec | Slow | | > 3 sec | Unusable | ## How to Reduce Latency ### Network - [Use CDN](https://www.mindstick.com/blog/305904/how-to-use-a-cdn-content-delivery-network-to-improve-site-speed) - Reduce round trips - Keep connections alive ### Application - [Async / non-blocking code](https://www.mindstick.com/interview/34235/what-is-the-async-and-await-pattern-in-c-sharp-when-should-you-use-it) - [Caching](https://www.mindstick.com/forum/161233/what-is-caching-and-why-is-it-used) - Efficient algorithms ### Database - [Indexing](https://www.mindstick.com/blog/303489/the-significance-of-indexing-in-databases-for-seo) - Query optimization - Read replicas ## Latency in Real-Time Systems - **WebSocket / SSE** → designed for low latency - **REST APIs** → higher latency per request - **Polling** → high latency & wasteful ## --- Original Source: https://www.mindstick.com/interview/34441/what-is-latency-in-software Copyright © MindStick Software Pvt. 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