Beginner LevelPostgreSQL
What are UNLOGGED tables and when should you use them for performance?
❓ Interview Prompt: Explain UNLOGGED tables (`CREATE UNLOGGED TABLE`), bypassing Write-Ahead Logging (WAL), 2x write speedup, and crash recovery risk.
UNLOGGED tables bypass writing data modifications to the Write-Ahead Log (WAL):
Performance & Risk:
•
2x Write Speedup: Writing data is significantly faster because WAL disk I/O is eliminated.
•
Crash Non-Durability: If PostgreSQL crashes, UNLOGGED tables are automatically truncated on recovery!
•
Use Cases: Ephemeral build staging tables, transient session stores, and ETL data transformations.
Code Implementation Example
sql
CREATE UNLOGGED TABLE staging_csv_imports (
raw_payload TEXT,
imported_at TIMESTAMPTZ DEFAULT NOW()
);💡Creating high-performance UNLOGGED tables for ephemeral staging data.
🎯 Interview Key Takeaway
Use UNLOGGED tables for transient staging data to double write performance, accepting that data is truncated if Postgres crashes.
#UNLOGGED#WAL Bypass#Performance#Staging#Beginner
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