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Advanced Topic 37 of 51 Databases

Replication

Copying data across servers for availability.

How it works

Replication keeps copies of data on multiple servers for availability, read scaling and disaster recovery. In primary-replica setups, writes go to the primary and changes stream to replicas by shipping the log, either synchronously, where the commit waits for the replica, or asynchronously, which is faster but can lose recent commits on failover. Multi-primary replication accepts writes in several places and requires conflict resolution.

Step-by-step walkthrough

  1. Writes go to the primary.
  2. Changes are streamed to replicas.
  3. The same stream reaches the second replica.
  4. Reads can be served by replicas.
  5. If the primary fails a replica is promoted, with replication lag as the risk.

Where it is used

Read-heavy applications direct queries to replicas, failover systems promote a replica when the primary fails, and geographically distributed copies reduce latency and survive regional outages.

Common pitfall

Asynchronous replicas lag, so reads may be stale; read-your-own-writes needs care. Failover can cause split brain if two nodes think they are primary. Replication is not a backup, since mistaken deletes replicate too. Monitor lag, test failover and design for eventual consistency.

Where it fits in the course

Replication is topic 37 of 51 in Databases, rated Advanced. It follows Database Partitioning. The next topic is Sharding.

Practice and explore

How to study this topic

  1. Read the explanation above and restate the definition in your own words.
  2. Open the interactive lesson and answer its mini quiz.
  3. Read the common pitfall, then write a short example that avoids it.
  4. Check your understanding in the Databases quiz, and revisit the topic if you miss a question.

Frequently asked questions

What is Replication?
Copying data across servers for availability. It belongs to Databases and is an advanced-level topic.
Where do people use Replication?
Read-heavy applications direct queries to replicas, failover systems promote a replica when the primary fails, and geographically distributed copies reduce latency and survive regional outages.
What is the most common mistake with Replication?
Asynchronous replicas lag, so reads may be stale; read-your-own-writes needs care.
What should I learn before this topic?
Start with Database Partitioning, the topic just before it in Databases.
How can I practice it?
Answer the mini quiz in the interactive lesson, then take the Databases quiz.
Is Replication hard to learn?
It is an Advanced topic. Expect to read the explanation more than once and to connect it with earlier topics. Working through a small example by hand helps most.
How long does it take to learn Replication?
Most learners can read the explanation and finish the interactive lesson in under an hour. Fluency comes from applying the idea, so plan a few short practice sessions with the quiz.
Which topics are related to Replication?
Database Partitioning, Sharding, Recovery and Logging are closely connected. The full list is in the related topics section of this page.
What should I study after Replication?
Continue with Sharding, the next topic in Databases.

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