Document known problems

[dgzlopes]

QuickPizza isn't perfect! It has a few problems:

• Backend:
  • If too many HTTP requests hit the service, latency grows to the sky.
    • Type? Performance issue.
    • Why? There is a global lock in the in-memory database, used by all requests.
    • How to find it? With metrics and traces (once we have them).
    • How to fix it? By not coupling everything with the same lock (some ops are more critical than others).
  • Name generation is unpredictable and slow.
    • This is triggered every time someone asks for a recommendation.
    • Type? Performance issue.
    • Why? Someone added a non-critical check in the core flow of the app.
    • How to find it? Ideally, with tracing (once we add it).
    • How to fix it? Removing the check.
  • In-memory database should store only the last ten pizza recommendations, but it stores them all.
    • This data is used in the admin panel.
    • Type? Performance issue (memory leak).
    • Why? Someone didn't think it was that important to set this limit.
    • How to find it? With metrics.
    • How to fix it? Refactoring the implementation to only store the last ten recommendations.
  • If requirements are too strict and can't be fulfilled, we return a random recommendation after a few tries.
    • Type? Functional issue.
    • Why? This edge case isn't handled properly.
    • How to find it? With Checks/Thresholds.
    • How to fix it? If a good recommendation can't be generated, return an error.
• Frontend:
  • If the recommendations API is under load, no feedback is given to the user (e.g., loading spinner)
    • And they can retry manually as many times as they want (putting even more load on the backend)

Peek.2023-06-22.14-08.mp4

• The Quotes API blocks rendering.
  • Type? -
  • Why? We make a call to this API on the onMount() section, and we block rendering until it finishes.
  • How to find it? With the disruptor, when running on Kubernetes, if we inject some delay, it is very easy to see.
  • How to fix it? We could add a loading spinner. But, in this case, given that this request isn't part of the core flow (it is just a random quote that we show), we should render other parts of the site even if this endpoint is slow.

Peek.2023-06-22.15-08.mp4

[RafalSkolasinski]

I am just going through materials in this repo and https://github.com/grafana/k6-oss-workshop.

I noticed that if set vus and durations to larger numbers then quickpizza becomes defunct.
Basically the replies are empty and see a lot of errors/warnings in logs like

quickpizza-1  | time=2024-12-02T21:55:37.638Z level=WARN msg="failed to perform db query" operation=INSERT duration=6.959µs query="INSERT INTO \"pizza_to_ingredients\" (\"pizza_id\", \"ingredient_id\") VALUES (101, 2)" err="constraint failed: UNIQUE constraint failed: pizza_to_ingredients.pizza_id, pizza_to_ingredients.ingredient_id (1555)"

quickpizza-1  | time=2024-12-02T21:55:37.639Z level=ERROR msg="Storing recommendation in catalog" err="making http request: Post \"http://localhost:3333/api/internal/recommendations\": POST http://localhost:3333/api/internal/recommendations giving up after 1 attempt(s)" user=23423

and remains unavailable until I restart it with docker compose restart quickpizza.

Is that also known issue? In seems that in this context most of examples / workshop materials are broken.