Optimise evaluation time?

[L-as]

Evaluating the derivation of a haskell.nix project seems to take a very long amount of time even if every IFD has already been built.
Maybe more processing could happen "inside" the IFD, so that more can be cached?

[ocharles]

On this I've seen next to no change in evaluation time with materialization. I dunno if that warrants a separate issue

[L-as]

"next to none" I assume, indeed, this is about the non-materialised case, but this should still be blazing fast, and not take ~10 seconds.

[L-as]

I just counted, and with a Ryzen 5 1600, it took ~15 seconds to do nix develop, without building anything!

[ocharles]

Sorry, I was saying that for me, evaluation times with materialization are exactly the same as materialization times without materialization.

[michaelpj]

We've observed this recently too, and we've actually dropped materialization in some projects for that reason. Unclear why though, it still seems like it should be a speedup!

Unfortunately, analysing the performance of Nix code is pretty difficult, I don't believe there's really anything like a profiler.

[L-as]

@michaelpj Just moving the evaluation into a derivation and import-ing it seems like an easy hammer to use.

[hamishmack]

This has been bugging me for a while.

Could it be related to the size of hackage.nix? One simple test might be to take hacakge.nix and strip out all the packages a slow project does not use. Then see if the project is still slow.

Is it how we use the module system for modules? I'm not sure how best to test this. The last time we looked the profiling tools in nix did not help (but I think that was about 2 years ago).

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[kokobd]

I find this still relevant. Can we reopen this, and document that materialization no longer provides significant improvements if we are not going to fix this soon?