Question 1

What is two-phase commit and its drawbacks?

Accepted Answer

**Target Audience:** Developers who know what a database transaction is and now meet data spread over several databases or services. No distributed-systems background assumed.
**Difficulty:** Medium
**Verified with:** Node 22.22 and Python 3.12 (both print identical output).

> **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact words an interviewer expects. All timings and counts come from running the examp

Question 2

What is the difference between optimistic and pessimistic locking?

Accepted Answer

**Target Audience:** Beginners to databases and concurrency — you know what a row, a transaction and an `UPDATE` are; locking is built up from there.
**Difficulty:** Medium
**Verified with:** Node 22.22 and Python 3.12 (both print identical output). PostgreSQL defaults quoted below were read with `SHOW` on a local PostgreSQL 16.15 server; the SQL patterns are shown for illustration and were not executed in this run.

> **How to read this doc:** Every idea is explained in plain language first, th

Question 3

What are blue-green and canary deployments?

Accepted Answer

**Target Audience:** Beginners to release engineering — you know what a server, a load balancer and a deploy are; every term is defined as we go.
**Difficulty:** Medium
**Verified with:** Node 22.22 and Python 3.12 (both print identical output). Kubernetes defaults are from the Kubernetes Deployment API reference; the canary definition is from the Google SRE Workbook, chapter 16, checked in October 2026.

> **How to read this doc:** Every idea is explained in plain language first, then tagged wi

Question 4

What is backpressure and how do you handle it?

Accepted Answer

**Target Audience:** Beginners who have built a service or a data pipeline and want to understand why a fast producer and a slow consumer cause outages, and how systems push back.
**Difficulty:** Medium
**Verified with:** Node 22.22 and Python 3.12 (the strategy simulation prints identical output in both); the Node.js stream example ran on Node 22.22 and reads its own default `highWaterMark`. The earlier 16 KiB default is cited from the Node.js v22.0.0 release announcement, as reported in commun

SYSTEM DESIGNDECODED.

Medium

What is two-phase commit and its drawbacks?

What is the difference between optimistic and pessimistic locking?

What are blue-green and canary deployments?

What is backpressure and how do you handle it?