Replication Slots and WAL Management
Understand replication slots for guaranteed WAL retention and advanced WAL file management techniques.
WAL: The Heart of PostgreSQL
At the core of PostgreSQL's reliability and replication lies the Write-Ahead Log (WAL). Think of WAL as a journal that records every change made to your database.
- Every transaction writes to WAL before data is committed to disk.
- This ensures data integrity, even if the server crashes.
- Standby servers use WAL to reconstruct changes from the primary, staying in sync.
The WAL Retention Challenge
By default, PostgreSQL reclaims old WAL files to save disk space. This is fine for a standalone server, but it creates a challenge for replication.
If a standby server falls too far behind, the necessary WAL files might have already been removed from the primary. This leads to:
- Replication failure: the standby can't catch up.
- Manual intervention: requiring a full re-sync of the standby.
All lessons in this course
- Cascading Replication
- Multi-Master Replication (BDR)
- Replication Slots and WAL Management
- Logical Decoding and Change Data Capture