On Thu., 12 Dec. 2019, 10:03 pm Mark Shannon, <m...@hotpy.org> wrote:

>
> Explicit limits are much easier to test. Does code outside the limit
> fail in the expected fashion and code just under the limit work correctly?
>
> What I want, is to allow more efficient use of resources without
> inconveniently low or unspecified limits. There will always be some
> limits on finite machines. If they aren't specified, they still exist,
> we just don't know what they are or how they will manifest themselves.
>

This is the main reason I'd like to see the PEP split into two distinct
aspects:

* articulating & testing specific limits (we already have some bigmem tests
that can only be run at full scale on server class machines with 20+ GiB of
RAM - don't forget that CPython runs on supercomputers, not just regular
machines).

* potentially lowering some specific limits in the CPython implementation

The first part is clearly valuable as a general capability, especially if
there's an API that lets different implementations report different limits.
For example, something like a "sys.implementation.limits" informational
API, modelled on the way that the top level "sys.implementation" data
structure already works.

Even when the limits are large, we have potential access to machines that
can accommodate them for testing purposes (e.g. I know at least one Linux
vendor that we're on good terms with that has servers with more than a
terabyte of RAM in their test fleet, and I presume other OS vendors and
cloud platform providers have similar capabilities).

By contrast, the second part really needs to be tackled on a case-by-case
basis, with a clear understanding of the kinds of failure modes we're
aiming to handle more gracefully, which kinds of performance improvements
we're aiming to enable, and which existing capabilities we'd be reducing.

Cheers,
Nick.


>
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