PostgreSQL: Backup, Recovery, and Replication in PostgreSQL

Logical vs Physical Backups#

Backups. The thing nobody cares about—until they desperately need it. Imagine your database crashes, and you’re left staring at a blank screen, contemplating life choices. Let’s make sure that never happens.

Differences Between Logical and Physical Backups#

• Logical backups: Export data as SQL statements. Think of it as a “copy-paste” version of your database.
• Physical backups: Copy raw database files. More like a “clone everything” approach.

When to Use Logical vs. Physical Backups#

• Use logical backups when migrating databases, copying subsets of data, or running away from bad schema decisions.
• Use physical backups when you need a full, bit-perfect copy of your database, including indexes and transaction logs.

Advantages and Limitations of Each Approach#

pg_dump and pg_restore#

If you’re not backing up your database with pg_dump, you might as well keep your life savings in Monopoly money.

Using pg_dump for Logical Backups#

pg_dump -U postgres -d mydatabase -F c -f backup.dump

Restoring Databases with pg_restore#

pg_restore -U postgres -d mydatabase -F c backup.dump

Exporting and Importing Data Using psql#

pg_dump -U postgres -d mydatabase -f backup.sql
psql -U postgres -d newdatabase -f backup.sql

Strategies for Large Database Backups#

• Use parallel dumps: pg_dump -j 4
• Compress backups: pg_dump -Fc | gzip > backup.gz
• Automate with cron jobs—because manual backups are for masochists.

Continuous Archiving and Point-In-Time Recovery (PITR)#

Because sometimes, “undo” is the greatest feature of all time.

Understanding Write-Ahead Logging (WAL)#

PostgreSQL writes every change to a log file before actually applying it. This means you can replay history, like a time traveler fixing past mistakes.

Enabling Continuous Archiving#

wal_level = replica
archive_mode = on
archive_command = 'cp %p /backup_location/%f'

Performing a Point-In-Time Recovery (PITR)#

1. Restore base backup.
2. Copy WAL files back.
3. Use recovery.conf to tell PostgreSQL when to stop.

recovery_target_time = '2024-03-21 12:00:00'

Automating Backup and Recovery Processes#

• Schedule backups using cron.
• Use pgBackRest for automated disaster recovery.
• Monitor logs—because blind faith never ends well.

Replication Strategies#

Replication: Because a single point of failure is a terrible idea.

Overview of Database Replication#

Replication means having a second (or third, or fourth) copy of your database running elsewhere, ready to take over if disaster strikes.

Setting Up Streaming Replication#

wal_level = replica
max_wal_senders = 3
hot_standby = on

On the standby server:

pg_basebackup -h primary_host -D /var/lib/postgresql/data -P -U replication_user

Configuring Logical Replication#

CREATE PUBLICATION my_pub FOR TABLE users;
CREATE SUBSCRIPTION my_sub CONNECTION 'host=primary dbname=mydb' PUBLICATION my_pub;

Using Third-Party Replication Tools: Slony-I, Bucardo#

If built-in replication doesn’t cut it, try:

• Slony-I: Table-based replication.
• Bucardo: Multi-master replication.

High Availability and Failover#

Because uptime is money, and downtime is just embarrassing.

Importance of High Availability in PostgreSQL#

Nobody wants to explain why the database was down for five hours.

Implementing Failover Mechanisms#

• Manual failover: Old-school but dangerous.
• Automatic failover: Smart, scalable, and saves your sanity.

Tools for Automatic Failover: Patroni, repmgr#

• Patroni: Automates failover with Etcd/Consul.
• repmgr: A simpler but effective option.

Monitoring and Maintaining Replication Setups#

SELECT * FROM pg_stat_replication;

Hands-On Exercise#

1. Perform a logical backup using pg_dump and restore it with pg_restore.
2. Configure continuous archiving and simulate a Point-In-Time Recovery (PITR).
3. Set up streaming replication between two PostgreSQL instances.
4. Test logical replication by replicating specific tables.
5. Implement a failover mechanism using Patroni or repmgr.

Backup before it’s too late. Replicate before disaster strikes. Automate unless you enjoy all-nighters. Your future self will be grateful.