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Can Postgres replace Redis as a cache

Disclaimer: This is a personal summary and interpretation based on a YouTube video. It is not official material and not endorsed by the original creator. All rights remain with the respective creators.

This document summarizes the key takeaways from the video. I highly recommend watching the full video for visual context and coding demonstrations.

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Introduction to Using Postgres as a Cache

Summary: The video explores the idea of using Postgres as a message broker and cache to replace Redis, sparked by a Twitter response and an article by Stefan Schmid. It questions whether Postgres, a relational database, can effectively substitute for Redis, which is known for its speed and is often used as a primary database or cache. Key Takeaway/Example: Redis handles millions of operations per second, making it ideal for caching, but the article suggests Postgres could reduce complexity by consolidating tools. Link for More Details: Ask AI: Postgres as Cache

Reasons to Replace Redis with Postgres

Summary: Postgres can simplify your tech stack if you're already using it, offering a familiar SQL interface for complex queries and potentially better cost efficiency by leveraging existing resources without adding new systems. Key Takeaway/Example: It reduces maintenance of multiple databases, improves resource utilization in budget-constrained setups, and keeps everything in one tool for faster development. Link for More Details: Ask AI: Benefits of Postgres Cache

Essential Features of a Caching Service

Summary: A good cache needs high performance for fast data access, expiration to remove outdated data, eviction policies for memory management, and simple key-value storage for efficient retrieval. Key Takeaway/Example: The goal is quick, up-to-date data access; Redis excels here with sub-millisecond responses and high throughput. Link for More Details: Ask AI: Caching Service Features

Turning Postgres into a Cache with Unlogged Tables

Summary: Use unlogged tables in Postgres to disable write-ahead logging (WAL), which boosts write performance by avoiding double writes and disk flushes, similar to turning off Redis's append-only file (AOF) for caching. Key Takeaway/Example: Unlogged tables sacrifice persistence for speed, as there's no WAL to recover from crashes, but this is acceptable for non-critical cache data. Link for More Details: Ask AI: Unlogged Tables in Postgres

Handling Expiration and Eviction in Postgres

Summary: Expiration requires stored procedures and the PG Cron extension for scheduling cleanups; eviction is optional but can be implemented with a last_read timestamp column and another procedure for LRU policy. Key Takeaway/Example: This adds complexity, as stored procedures can leak business logic into the database, unlike Redis's built-in eight eviction policies. Link for More Details: Ask AI: Expiration and Eviction in Postgres

Performance Comparison Between Postgres and Redis

Summary: Benchmarks show unlogged tables double write speed over logged ones, but read speeds are similar due to shared buffers; Redis is 85% faster overall, with much higher request rates. Key Takeaway/Example: Even running Postgres in memory (via tmpfs) doesn't match Redis, due to overhead like locks and buffer management. PG Bench results confirm comparable read performance between logged and unlogged tables. Link for More Details: Ask AI: Postgres vs Redis Performance

Conclusion: Should You Replace Redis with Postgres?

Summary: Postgres unlogged tables help with writes but not reads, and lack built-in features like easy expiration/eviction; Redis is superior for caching to prevent database overload and ensure fast retrieval. Key Takeaway/Example: Stick with Redis for dedicated caching—it's simpler, faster, and more feature-rich than trying to adapt Postgres. Link for More Details: Ask AI: Replacing Redis with Postgres

About the summarizer

I'm Ali Sol, a Backend Developer. Learn more: