What is Master-Slave in PostgreSQL?

Master-slave architecture in PostgreSQL, also referred to as primary-replica replication, is a widely used solution for database workload distribution, improving performance and ensuring data redundancy. In this article, We will learn about What is master-slave in PostgreSQL in detail by understanding various aspects in detail.

What is Master-Slave in PostgreSQL?

• Master-slave architecture in PostgreSQL is one of the frequently deployed solutions of database workload distribution, improving performance and ensuring data redundancy.
  
• In this setup, one database server, known as the master or primary, manages all write operations, while one or more secondary databases, called slaves or replicas, mirror the masters data.
  
• This architecture is essential for enhancing database performance and availability.

What is PostgreSQL Master Slave Replication?

PostgreSQL Master-Slave replication, sometimes called Primary-Replica replication, is a database copy/replication where data from one PostgreSQL database (called the master or primary) is copied to another PostgreSQL database or databases, sometimes called slaves or replicas.

The master performs all writes (inserts, updates, deletes) whereas the replicas mirror the changes in real-time/near real-time. Copies are read-only. They are used for distributing read workloads and for providing high availability, in case of a failure of the primary server.

Master-Slave Replication Important Features:

• Real-time data replication: modifications made to the master are broadcast to the replicas almost in real time.
  
• Load balancing: You can offload read queries to the replicas, which means that the load is distributed on both primary and replica.
  
• Fault tolerance: When a master fails, one of these replicas could be promoted to take over to minimize downtime.
  
• The replication model thus guarantees data redundancy and workload distribution, which makes the database available most of the time.

Why is Master-Slave Replication Important in PostgreSQL?

PostgreSQL master-slave relations are important for several reasons.

• Load Balancing: They offer, on the one hand, load balancing by directing read queries towards slave databases to reduce the overall load on the master; the performance and response times improve for all users.
  
• High Availability: On the other hand, it guarantees high availability in case a master database fails because a slave can quickly be promoted to become a new master, ensuring minimal downtime and access to data.
  
• Data Redundancy: A slave database is a form of redundancy in that it can serve as the backup in the event data gets lost or corrupted on the master.
  
• Backup and Maintenance: Slave databases can be used without affecting the performance of the master, for backup purposes thus ensuring service continuity while similar data remains safe.
  
• Geographical Distribution: Deploying slaves across different geographical locations will be able to provide access to data for users in those respective regions more quickly and simultaneously allow for disaster recovery solutions.

Configuring Master-Slave Replication

Step 1: Edit the MySQL Configuration File (Master)

Open the MySQL configuration file on the master server (usually located at /etc/mysql/my.cnf or /etc/my.cnf).

Add or modify the following settings:

[mysqld]
server-id=1           # Unique ID for the master server
log_bin=mysql-bin     # Enables binary logging (required for replication)

Step 2: Create a Replication User

Login to your MySQL server as the root user.

mysql -u root -p

Create a user for replication and grant necessary privileges:

CREATE USER 'replica_user'@'%' IDENTIFIED BY 'your_password';
GRANT REPLICATION SLAVE ON *.* TO 'replica_user'@'%';
FLUSH PRIVILEGES;

Step 3: Obtain Master Log File and Position

Run the following command to get the binary log file and position that will be used by the slave to start replication:

SHOW MASTER STATUS;

Expected Output:

Step 4: Restart the MySQL Service

Restart the MySQL service to apply the changes:

sudo systemctl restart mysql

Configuring Slave Database with the screenshot of the implementation

1. Slave Database Configuration

Requirements

1. PostgreSQL should be installed on the master and slave.
2. The network connectivity should be in place between the master and slave.

2. Master Server

1. Open the postgresql.conf on the master.
2. Set wal_level to replica
3. max_wal_senders andwal_keep_segments
4. In pg_hba.conf change the configuration to allow the slave to connect in order to replicate.

3. Creation of Replication User

Run the SQL command that creates a replication user

Slave Server

1. Prepare recovery configuration file, usually recovery.conf on the server:
2. Give the connection details of the master.
3. If replication slots are used: Explain replication slot.

Starting the Slave Server

Begin from the slave server by starting the PostgreSQL service and checking that replication is taking place.

Configuration Verification

Use SQL commands to check for updates from the master side in the slave.

Post-Configuration Operations

If a master-slave relationship is established in PostgreSQL, then some of the most important operations and things to remember are as follows:

• Data Synchronization: The slave will always fetch changes from the master, apply them, so the slave must always have the latest data.
  
• Read Queries: An application can begin sending read queries to the slave database(s), so achieving optimal load balancing on a slave node.
  
• Monitoring: The slave has to be up-to-date with the master's replication status. The administrators have to monitor the lag times and error logs so that they are corrected well in time.
  
• Failover Planning: The organizations should have a clearly defined failover procedure. If the master goes down, the slave can immediately take over the role of master such that the downtime will be highly minimized.
  
• Backup Procedures: The slave can be taken up for the scheduled backups which do not affect the performance of the master in order to ensure data safety.
  
• Maintenance: Systematic maintenance, including but not limited to updates or patches, should be carried out in a fashion that does not affect the replication process during such periods of time.
  
• Testing: Test failover and recovery plans at regular intervals so that the system can respond accordingly in case of unexpected failures.

Common Use Cases for Master-Slave Replication

• High Availability Systems: Such applications need to be continuously available, even during maintenance or hardware failures.
• Read-heavy applications: similar to an e-commerce site or a social networking site that may have far more reads than writes.
• Disaster recovery solutions Organisations with a high demand need to incorporate disaster recovery solutions mechanisms into place.
• Geo-Distributed Systems: Applications where read operations need to be made low-latency by geographically dispersed users.

Conclusion

Thus, master-slave replication in PostgreSQL is one of the most powerful strategies for improving database performance with high availability and also for securing data redundancy. The separation of read and write operations between master and slave databases lets organizations achieve much better load distribution and fewer chances of data loss or downtime through system failure. Whether in asynchronous mode for maximum throughput or in synchronous mode for database consistency, master-slave replication offers flexible and scalable solutions for applications that require reliable data architecture. However, proper setup, monitoring, and maintenance of this replication are important to really benefit from the replication strategy.