Zhu Yuechen's Tech Notes

Sun, 26 Apr 2026 14:22:48 GMT

Welcome to my second brain — a collection of engineering notes from work, side projects, and things I’ve learned the hard way.

Tagging Convention

Sun, 26 Apr 2026 14:22:48 GMT

Tags are how you filter across folders. The folder is where a note lives; tags are what it’s about. A note can have multiple tags.

Site Workflow

Sun, 26 Apr 2026 14:22:48 GMT

Reference for adding and maintaining content on this site.

OpenFGA (ReBAC)

Sun, 26 Apr 2026 00:00:00 GMT

What it is OpenFGA implements Relationship-based Access Control (ReBAC) from Google’s Zanzibar paper.

Metabase H2 → PostgreSQL RDS Migration

Sun, 26 Apr 2026 00:00:00 GMT

H2 file layout metabase.db.mv.db — main data file metabase.db.trace.db — transaction logs Pre-migration uptime && top -bn1 | head -20 # system health sudo du -sh /metabase.db/ # size check Size → RDS instance sizing: <500MB small, 500MB–2GB medium, >2GB large.

Mongoose Schema vs TypeScript Interface

Sun, 26 Apr 2026 00:00:00 GMT

The silent ignorer If a field exists in the TypeScript interface but not in the Mongoose schema, Mongoose silently drops it on save().

Cache Invalidation After Direct SQL Updates

Sun, 26 Apr 2026 00:00:00 GMT

What happened Direct SQL fix to update_exclusions corrected the DB, but Redis still held stale data.

Use context.Background() for Redis Cleanup Operations

Sun, 26 Apr 2026 00:00:00 GMT

Problem Warning Silent failure — If the request context is cancelled (timeout, panic), Del returns immediately with no error — the lock is never released, the queue backs up, consumers stall.

Redis Logical Databases & Debugging Locks

Sun, 26 Apr 2026 00:00:00 GMT

Logical databases Redis supports databases 0–15 in a single instance — separate namespaces, no key collisions.

Deduplicating Messages Across Pods with Redis SETNX

Sun, 26 Apr 2026 00:00:00 GMT

Problem Scaled from 1 → 3 replicas. Started getting 3 duplicate polling messages every 30 seconds.