Tutorials PostgreSQL Tutorial

Replication Basics — Complete Guide

Replication Basics — Complete Guide: free step-by-step lesson with examples, common mistakes, and interview tips — part of PostgreSQL Tutorial on Toolliyo Academy.

8 min read Updated 8/19/2026

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PostgreSQL Tutorial · Lesson 39 of 100

Replication Basics

SQL → Advanced

SQL · 1 — Queries · ~6 min · PostgreSQL — Transactions & MVCC

What is this?

Replication copies data from primary to standby servers — physical (byte-for-byte WAL) or logical (row changes). Standbys can serve read-only queries or take over on failure.

Why should you care?

PostgresVerse production runs primary in Mumbai and standby in Hyderabad for disaster recovery and read scaling.

See it live — copy this example

Run in pgAdmin or psql.

-- On primary (read settings)
SHOW wal_level;
SELECT client_addr, state, sync_state
FROM pg_stat_replication;

What happened?

wal_level replica enables physical streaming.
pg_stat_replication lists connected standbys, replay state, and sync mode — empty until you configure replication.

Practice next

Confirm wal_level is replica or logical on primary.
Review postgresql.conf and pg_hba.conf replication entries (lab docs).
Query pg_stat_replication after lab standby connects.
List replication slots: SELECT * FROM pg_replication_slots;
Check replay lag: now() - pg_last_xact_replay_timestamp() on standby.

Remember

WAL stream keeps standbys near real-time. Physical replication copies whole cluster. Logical replication copies selected tables.

PostgresVerse DR baseline

Startup configures one synchronous standby before RBI audit of payment data.

Outcome: RPO/RTO documented with measured replay lag under 1s.

Interview prep for this lesson

Practice these questions aloud after reading—each links to a full structured answer.

Junior Detailed

Explain SQL queries in the context of PostgreSQL.

Short answer: Interviewers want a crisp definition, a practical example from your projects, and awareness of trade-offs—not textbook dumps. Explain a bit more How to structure your answer (60–90 seconds) Define SQL queri…

What are common mistakes teams make with Schema design when using PostgreSQL?

Short answer: Interviewers want a crisp definition, a practical example from your projects, and awareness of trade-offs—not textbook dumps. Explain a bit more How to structure your answer (60–90 seconds) Define Schema de…

Senior Detailed

How would you debug a production issue related to Transactions in a PostgreSQL application?

Short answer: Interviewers want a crisp definition, a practical example from your projects, and awareness of trade-offs—not textbook dumps. Explain a bit more How to structure your answer (60–90 seconds) Define Transacti…

Compare two approaches to Indexing—when would you choose each?

Short answer: Interviewers want a crisp definition, a practical example from your projects, and awareness of trade-offs—not textbook dumps. Explain a bit more How to structure your answer (60–90 seconds) Define Indexing…

Junior Detailed

Describe a real-world scenario where Normalization mattered in a PostgreSQL project.

Short answer: Interviewers want a crisp definition, a practical example from your projects, and awareness of trade-offs—not textbook dumps. Explain a bit more How to structure your answer (60–90 seconds) Define Normaliza…

All course Q&A Practice exams

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