Cascading Replication
Implement cascading replication to distribute the load of a primary server by having standbys replicate from other standbys.
Cascading Replication is a free Advanced PostgreSQL: Indexing, Partitioning, Replication lesson on CoddyKit — lesson 1 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Advanced PostgreSQL: Indexing, Partitioning, Replication learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
What is Cascading Replication?
Welcome to Cascading Replication! In typical PostgreSQL replication, all standby servers connect directly to the primary server.
However, for larger setups or when you need many read replicas, this can put a lot of load on the primary. Cascading replication offers a solution.
It means a standby server can itself act as a primary for other standbys, forming a chain.
How the Replication Chain Works
Imagine a chain: The primary server sends its Write-Ahead Log (WAL) to a first standby (let's call it Standby A).
Then, Standby A, instead of just consuming the WAL, also acts as a source, sending that same WAL data to a second standby (Standby B).
This creates a flow: Primary → Standby A → Standby B. Standby A is an 'intermediate' standby.
Key Benefits of Cascading
Why go through the trouble of chaining standbys? Cascading replication offers several advantages:
- Reduced Load on Primary: The primary only needs to send WAL to Standby A, not to all standbys directly.
- Scalability for Reads: You can create many read replicas without overwhelming the primary's network or I/O.
- Geographical Distribution: Standbys can be spread across different data centers, with intermediate standbys bridging the distance.
Preparing the First Standby (Standby A)
The first step is to set up Standby A as a regular streaming replication standby. This involves taking a base backup from the primary and configuring Standby A to connect to the primary.
The key here is that Standby A must also be configured to send WAL files to other standbys, not just receive them.
Configuring Standby A to be a Source
For Standby A to act as a source for other standbys, you need to adjust its PostgreSQL configuration (`postgresql.conf`).
The important parameters are wal_level and max_wal_senders. hot_standby should also be on to allow queries.
wal_level = replica
max_wal_senders = 5 -- Or more, for primary and other standbys
hot_standby = onStandby B: Connecting to Standby A
Now, for Standby B, instead of pointing its primary_conninfo to the actual primary server, you point it to Standby A.
This tells Standby B to receive its WAL stream from Standby A.
primary_conninfo = 'host=standby_a_ip port=5432 user=replication_user password=YOUR_PASSWORD'
primary_slot_name = 'standby_b_slot' -- Optional, for guaranteed WAL
hot_standby = onInitializing Standby B's Base
Just like any new standby, Standby B needs an initial copy of the data. You can take this base backup directly from the primary, or, more commonly in a cascading setup, you can take it from Standby A.
Using Standby A for the base backup further reduces load on the primary.
# On Standby B, after stopping PostgreSQL
pg_basebackup -h standby_a_ip -p 5432 -U replication_user -D /var/lib/postgresql/data -F p -Xs -P -RMonitoring the Cascade
It's crucial to monitor the health of your cascading setup. The pg_stat_replication view is your best friend.
On the primary, you'll see Standby A connected. On Standby A, you'll see Standby B connected.
-- On Standby A (or Primary):
SELECT application_name, client_addr, state, sync_state FROM pg_stat_replication;Practical Use Cases
Cascading replication shines in scenarios where:
- You have a high number of read queries and need many read replicas.
- You want to offload backup operations to a standby, but also need other standbys for reads.
- You are distributing your database across multiple regions and want to minimize cross-region traffic from the primary.
- You're building complex disaster recovery tiers.
Cascading Replication Quiz
Let's test your understanding of cascading replication.
Recap: Cascading Replication
In this lesson, we explored cascading replication, a powerful architecture for scaling PostgreSQL read replicas and distributing replication load.
You learned how standbys can form a chain, with one standby replicating from another, and the key configurations and benefits, such as reduced primary load and enhanced read scalability.
This technique is essential for robust, distributed PostgreSQL environments.
Frequently asked questions
Is the “Cascading Replication” lesson free?
Yes — the full text of “Cascading Replication” is free to read here on the web, and the Advanced PostgreSQL: Indexing, Partitioning, Replication course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Advanced PostgreSQL: Indexing, Partitioning, Replication course, upgrade to CoddyKit PRO.
What will I learn in “Cascading Replication”?
Implement cascading replication to distribute the load of a primary server by having standbys replicate from other standbys. You practise Advanced PostgreSQL: Indexing, Partitioning, Replication with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Advanced PostgreSQL: Indexing, Partitioning, Replication?
No prior experience is required. Advanced PostgreSQL: Indexing, Partitioning, Replication on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Cascading Replication” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Advanced PostgreSQL: Indexing, Partitioning, Replication lesson?
Yes. Every Advanced PostgreSQL: Indexing, Partitioning, Replication lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.