API occasionally unstable with not usable exceptions or strange HTTP error codes

We contact OpenML REST API inside our CI with few requests. Every so and so our tests fail. It seems that because the server is under the load. See for example this run: https://gitlab.com/datadrivendiscovery/d3m/-/jobs/924199064

So when using OpenML Python package we get:

openml.exceptions.OpenMLServerException: Database connection error. Usually due to high server load. Please wait for N seconds and try again. - None

Why it says N seconds? This is hard to wrap, wait, and retry? Or am I missing some information?

When using REST API directly, the error is:

requests.exceptions.HTTPError: 412 Client Error: Precondition Failed for url: https://www.openml.org/api/v1/json/task/168861

I do not think 412 is the right one here. 412 is used for cache validation. I think you want 429 Too Many Requests with Retry-After header. Or 503 Service Unavailable.

Start by examining the REST API handling for /api/v1/json/task/168861 and the OpenML Python package's OpenMLServerException behavior. Reproduce the failure using the linked CI run and compare the 412 response with the reported 429 or 503 alternatives and Retry-After information. Done means transient server-load failures expose a usable retry signal and appropriate HTTP response.