0.5.x Extremely slow server performance

Gorse version 0.5.4

Describe the bug There's a huge difference in the API performance between version 0.4.x and 0.5.x.

To Reproduce New setup: Gorse (master, worker, server) 0.5.4, Redis 8.6.0, MySQL 8. Old setup: Gorse (master, worker, server) 0.4.16, Redis 8.6.0, MySQL 8.

Version 0.4.16 handles 300 rps on the API (POST /feedback and GET /recommend/xyz) with 3ms response time, while training. Version 0.5.4 slows down to 900ms on POST /feedback, and 15s GET /recommend/xyz while training. Drops to normal 3ms when stopping "master" container.

Expected behavior Performance should be similar across versions.

Additional context

• Server A: Gorse + Redis server with 88 cores, 1TB RAM
• Server B: MySQL Server with 56 cores, 750GB RAM
• About 12M feedbacks and 400k users per day. 40k items, +300 per day.
• Most settings on config.toml are set to default, except n_jobs, periods and cache