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Master-slave

Learn the primary and replica structure.

Master-slave

In the master-slave (primary-replica) model, writes go only to the master. Slaves copy from the master and serve read queries.

CREATE SUBSCRIPTION sub_orders
CONNECTION 'host=master dbname=shop'
PUBLICATION pub_orders;

This query writes to master, reads from slave.

Master-slave — details

If the read load is heavy, you add more slaves; each shares read traffic. But write speed is capped by the master alone.

Practice Master-slave

Connect the sub_orders subscription to the pub_orders publication with CONNECTION 'host=master dbname=shop'.

Starter code

query.sql
-- master-slave
CREATE SUBSCRIPTION sub_orders

Sample solution

query.sql
CREATE SUBSCRIPTION sub_orders CONNECTION 'host=master dbname=shop' PUBLICATION pub_orders;

Expected output

CREATE SUBSCRIPTION

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Create a subscription

Question 
CREATE SUBSCRIPTION sub_orders CONNECTION 'host=master dbname=shop' PUBLICATION ____
Answer 
CREATE SUBSCRIPTION sub_orders CONNECTION 'host=master dbname=shop' PUBLICATION pub_orders

Explanation: pub_orders is the right answer.

2 Which node receives writes?

  • The replica (slave)
  • A reader
  • The primary (master) Correct answer
  • Both

Explanation: Writes go only to the master.

3 Master-slave: match the terms

Term Meaning
master master
slave slave
write write
read read

All lessons in Expert

1 Database design

  1. ER model
  2. Cardinality
  3. Surrogate keys
  4. Natural keys
  5. Denormalization
  6. Summary - Design

2 Index tuning

  1. B-tree structure
  2. Covering index
  3. Partial index
  4. Index selectivity
  5. Index maintenance
  6. Summary - Index tuning

3 Query optimizer

  1. What is an optimizer?
  2. Statistics
  3. Cost model
  4. Join strategies
  5. Plan cache
  6. Summary - Optimizer

4 Project: Performance tuning

  1. Scenario design
  2. Reading plans
  3. Adding indexes
  4. Rewriting queries
  5. Comparing results

5 Replication and sharding

  1. What is replication?
  2. Master-slave
  3. Sync vs async
  4. What is sharding?
  5. Shard key
  6. Summary - Replication and sharding

6 Distributed and big data

  1. Distributed queries
  2. MPP
  3. Columnar storage
  4. SQL on Hadoop
  5. SQL vs NoSQL
  6. Summary - Distributed and big data

7 Security and backup

  1. SQL injection
  2. Parameterised queries
  3. Authorisation
  4. Backup
  5. Recovery
  6. Summary - Security and backup

8 Expert final

  1. Design challenge
  2. Optimization challenge
  3. Security challenge
  4. Backup challenge