Disabling on-disk cache

[sklam]

Although NUMBA_CACHE_DIR allows us to move the cache directory to another location, I think that for HPC systems we actually want to have a mechanism for disabling caching completely. We sometimes run mpi4py applications with >100K processes, and it is much better to have all those processes independently spend a few seconds compiling things rather than trying to read them from disk.

Is there any hope of a "NUMBA_CACHE_DISABLE" switch to forcibly override any cache=True options globally?

Originally posted by @tskisner in #3470 (comment)

[ickc]

To reiterate, I think I read somewhere that when Numba reaches v1.0, Numba will default to cache if the decorator doesn't specifically disabled it. So it would be important to have this env. var. option (or any sort of "global kill switch") to override this behavior before Numba reaching v1.0. Could we add this issue as part of the v1.0 milestone?

[seibert]

Likely we will do this sooner, but good to note the need before caching is enabled by default.

[leofang]

On the GPU side, I would view this feature request as more or less the opposite of that in #4389, in which we don't want any compiling to happen. It'd be good to have both features in 1.0 and let users decide the deployment strategy in a HPC system.

[seibert]

I think we'll want to do this as NUMBA_CACHE_OVERRIDE=always|never