Relax timestamp check in precompiled images?

[tanmaykm]

I am running into an issue when I transfer precompiled Julia packages to a GlusterFS volume.
The loader always finds the precompiled files stale. I see this:

INFO: JL_DEBUG_LOADING: Rejecting stale cache file /mnt/pkgdefault/.julia/lib/v0.5/JSON.ji (mtime 1.4881987029958088e9) because fil
e /mnt/pkgdefault/.julia/v0.5/JSON/src/JSON.jl (mtime 1.488198702995808e9) has changed.                                            
INFO: Recompiling stale cache file /mnt/pkgdefault/.julia/lib/v0.5/JSON.ji for module JSON. 

It seems to be due to timestamp precision on GlusterFS being different.

I think timestamp precision can be different for different filesystems, 1 sec being the lowest among the recent systems. Would it be better to relax the timestamp checking condition to 1 sec? (that is, checking floor(ftime) != floor(ftime_req) here instead).

Ref. #13606: similar issue with docker

[tkelman]

Changes that happen in less than a second should still trigger recompilation, so no I don't think relaxing the check in that way is an appropriate fix.

[tanmaykm]

I wonder if there is a way to get the precision supported by the underlying filesystem. The check could then use that information. No?

[tkelman]

Dunno. Only one of the values gets truncated, right? Extending the way the docker check was done to a different allowed level of truncation should be fine and wouldn't be that likely to have false positives. Just don't take the floor of both sides.

[tanmaykm]

Yeah, sounds good. Will send a PR.