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

Explain database indexing and B-trees

Accepted Answer

**Target Audience:** Beginners to databases — you know what a table and a row are; no data-structures background needed beyond "sorted lists are easy to search".
**Difficulty:** Medium
**Verified with:** Node 22.22, Python 3.12, Go 1.24 and Java 21 (all four 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. Behaviour shown comes from running the exa

Question 3

What is a write-ahead log (WAL)?

Accepted Answer

**Target Audience:** Beginners to database internals — you know a database stores data on disk and that a server can crash; everything else is defined as we go.
**Difficulty:** Medium
**Verified with:** Node 22.22 and Python 3.12 (both print identical output). PostgreSQL settings were read with `SHOW` on a local PostgreSQL 16.15 server; SQLite behaviour was checked with SQLite 3.45.1 from Python.

> **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 I

Question 4

What is a Bloom filter and when is it useful?

Accepted Answer

**Target Audience:** Beginners to system design — you know what a hash function and a set are; the probability is worked through step by step.
**Difficulty:** Medium
**Verified with:** Node 22.22, Python 3.12, Go 1.24 and Java 21 (all four 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. Error rates and sizes come from running the example; the **Ve

SYSTEM DESIGNDECODED.

Medium

What is two-phase commit and its drawbacks?

Explain database indexing and B-trees

What is a write-ahead log (WAL)?

What is a Bloom filter and when is it useful?