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Anubhav Kumar

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The Anubhav portal was launched in March 2015 at the behest of the Hon'ble Prime Minister for retiring government officials to leave a record of their experiences while in Govt service .

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Anubhav Kumar

Anubhav Kumar

13-Jan-2026

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
  • Reduce round trips
  • Keep connections alive

Application

Database

  • Indexing
  • 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

 

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