- 27 Nov, 2025
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Hot Standby in PostgreSQL
Hot Standby, Hot Standby Feedback & Conflict Handling in PostgreSQL
High availability (HA) is a critical requirement for modern database systems. PostgreSQL provides robust features such as Streaming Replication, Hot Standby, and Conflict Handling to ensure uninterrupted database operations. These features are essential topics in any professional postgresql dba online training and are widely used in enterprise deployments. Understanding how they work helps DBAs maintain stable, scalable, and reliable environments.
In this blog, we explain Hot Standby, Hot Standby Feedback, and conflict handling, especially aimed at learners of postgresql for dba training programs.
What Is Hot Standby in PostgreSQL?
Hot Standby is a PostgreSQL feature that allows a standby replica to:
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Continuously receive WAL (Write-Ahead Log) data from the primary server
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Replay WAL records
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Accept read-only queries from applications
This means the standby node is actively available for reporting, analytics, and query load balancing even while replication is happening.
✔ Benefits of Hot Standby:
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Read scalability
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Better resource utilization
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Faster disaster recovery
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Offloading heavy queries from the primary
These advantages make Hot Standby an important chapter in postgresql dba online training as it helps DBAs design high-availability architectures.
What Is Hot Standby Feedback?
Hot Standby Feedback solves a major issue:
Standby queries getting canceled due to conflicts with WAL replay.
🔸 The Problem Without Feedback:
When the primary modifies or deletes rows, it sends WAL to the standby.
But if a long-running query is running on the standby, replaying WAL may conflict with it.
PostgreSQL resolves this by canceling the standby’s query to keep replication moving.
This is not ideal for analytical workloads.
The Solution — hot_standby_feedback
When you enable:
The standby informs the primary about active queries so that the primary:
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Does NOT vacuum away tuples
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Does NOT remove dead rows
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Avoids cleanup that would cause standby conflicts
This allows long-running read queries on the standby to continue without interruption.
This concept is frequently explained in postgresql for dba courses because it directly affects performance tuning and replication behavior.
Conflict Handling in Hot Standby
Even with Hot Standby, conflicts can occur during WAL replay. Conflicts mainly arise due to:
✔ Query Conflicts
Queries on standby conflict with WAL replay operations such as:
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DELETE
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UPDATE
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VACUUM
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DROP
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TRUNCATE
✔ Snapshot Conflicts
When the primary removes rows needed for MVCC snapshots used by standby queries.
✔ Lock Conflicts
DDL statements (like ALTER TABLE), which require ACCESS EXCLUSIVE locks, may create lock conflicts on standby.
These conflicts are handled using internal rules such as:
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Query cancellation
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Snapshot invalidation
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Delay in WAL replay (temporary)
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Using hot_standby_feedback to reduce conflicts
Conflict handling is a core concept taught in postgresql dba online training because it directly influences replication design and query performance.
Types of Hot Standby Conflicts
a. Snapshot Conflicts
Occurs when WAL changes require removal of old versions still needed by standby queries.
b. Buffer Pin Conflicts
Happens when a standby query holds a buffer pin that WAL replay wants to modify.
c. Lock Conflicts
DDL changes on the primary can block standby query execution.
d. Vacuum Conflicts
Vacuum removes dead tuples on primary that are still being read on standby.
Learning how to diagnose and resolve these conflicts is a key skill in postgresql for dba training programs.
How PostgreSQL Resolves Standby Conflicts
PostgreSQL uses the following steps:
1. Conflict Resolution Policies
Controlled via:
These parameters decide how long the standby waits before canceling queries.
2. Query Cancellation
If replay cannot wait, PostgreSQL cancels the conflicting query.
3. Delaying WAL Replay
Standby can temporarily pause WAL replay to let the query finish.
4. Hot Standby Feedback
Prevents certain conflicts by informing primary about standby queries.
These mechanisms ensure that both replication and read-only workloads remain stable.
Why These Concepts Matter for DBAs
Every DBA working with high availability must understand:
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How standby nodes behave
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What happens when long-running queries run on standby
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How replication conflicts affect production
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How to tune parameters to prevent disruptions
These topics are covered deeply in postgresql dba online training because they enable DBAs to build reliable and high-performance replication setups.
Conclusion
Hot Standby, Hot Standby Feedback, and conflict handling are crucial features for maintaining stable and efficient PostgreSQL replication. They allow standbys to serve real-time read workloads while ensuring consistency with the primary. These concepts are foundational topics in postgresql for dba courses and must be mastered by anyone handling production PostgreSQL environments.
Understanding how to tune these settings ensures smoother replication, fewer query cancellations, and better overall database availability.
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Happy learning!
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