PostgreSQL High Availability Options: A Comprehensive Guide
High availability (HA) ensures that a PostgreSQL database remains accessible and operational, even during hardware failures, maintenance, or unexpected outages. PostgreSQL offers various HA solutions, including replication, clustering, and failover mechanisms. This guide explores the most common high availability options in PostgreSQL, with explanations, configurations, and examples.
Key High Availability Options in PostgreSQL
1. Streaming Replication
Streaming replication allows a standby server to replicate data from a primary server in real time. It ensures a near-zero recovery point in case of primary server failure.
Steps to Configure Streaming Replication:
1. Enable WAL Archiving: Add the following in the postgresql.conf file:
wal_level = replica max_wal_senders = 5 synchronous_commit = on
2. Create a Replication Role:
CREATE ROLE replication_user WITH REPLICATION PASSWORD 'password' LOGIN;
3. Base Backup: Use pg_basebackup to create a backup of the primary server:
pg_basebackup -D /var/lib/postgresql/replica -Fp -Xs -P -h primary_host -U replication_user
4. Configure Standby Server: Create a recovery.conf or set standby.signal with:
primary_conninfo = 'host=primary_host port=5432 user=replication_user password=password'
2. Logical Replication
Logical replication enables fine-grained replication by allowing specific tables or databases to be replicated.
Setup for Logical Replication:
1. Create a Publication on Primary:
CREATE PUBLICATION my_pub FOR TABLE my_table;
2. Create a Subscription on Standby:
CREATE SUBSCRIPTION my_sub CONNECTION 'host=primary_host dbname=mydb user=replication_user password=password' PUBLICATION my_pub;
3. Failover with Patroni
Patroni is a PostgreSQL clustering solution for managing high availability.
Steps:
1. Install Patroni, etcd/Consul, and HAProxy.
2. Configure Patroni with a YAML file:
scope: postgres_cluster
namespace: /pg/
name: node1
postgresql:
data_dir: /data/postgresql
bin_dir: /usr/pgsql-12/bin
parameters:
wal_level: replica
max_wal_senders: 5
3. Start Patroni and verify failover capability.
4. Cloud-Based High Availability
Cloud platforms like AWS, Azure, and Google Cloud offer managed PostgreSQL services with built-in HA. For instance, AWS RDS Multi-AZ deployment provides automatic failover across availability zones.
Example: Testing Streaming Replication
Primary Server Configuration:
# Edit postgresql.conf wal_level = replica max_wal_senders = 5 synchronous_commit = on # Reload configuration pg_ctl reload
Standby Server:
# Use pg_basebackup to initialize pg_basebackup -D /var/lib/postgresql/data -Fp -Xs -P -h 192.168.1.10 -U replication_user # Create standby.signal for replication touch /var/lib/postgresql/data/standby.signal
Testing:
1. Insert data into the primary:
Code:
INSERT INTO test_table (id, name) VALUES (1, 'Test');
2. Check if the standby replicates the data:
Code:
SELECT * FROM test_table;
Explanation:
1. High Availability Mechanisms:
2. Recovery and Failover:
3. Cloud HA:
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