schema: Memory thresholds should never be exactly 0.0.

[stuarteberg]

In the config, memory thresholds such as distributed.worker.memory.terminate should never be exactly 0.0.
Instead, config should use false to disable memory management.

This one bit me recently. My older dask config files used 0.0 to disable the memory management features. That worked because older versions of distributed interpreted the value 0.0 to be equivalent to false for these fields. But in newer versions, only false works. (I suspect the change occurred in #5904.)

Nowadays, if the config says 0.0, then distributed interprets that literally -- and no memory can be used at all without incurring the wrath of the memory manager!

An easy "fix" is to disallow 0.0 in the user's config. In json schema, exclusiveMinimum: 0 ensures that the value 0.0 itself is not permitted by the schema.

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• Tests added / passed
• Passes pre-commit run --all-files

[mrocklin]

Hi @stuarteberg 👋

@crusaderky I suspect that you understand this topic better than I do. Would you be comfortable owning this issue?

[crusaderky]

This makes sense to me. It avoids us having to set up over-complicated use case tests between 0 and False.

[stuarteberg]

@crusaderky The CI has sporadic failures, but I think they're unrelated to this change. I'm not sure if there's anything else to do in this PR. (Do schema changes require unit tests?)

Unless you have any suggestions, I think this is good for review/merge.

[mrocklin]

Thanks @stuarteberg !