[yt-users] Performance when using derived fields

[Daniel Fenn]

Hi everyone. Is it normal for slices to take substantially longer to be
created if they're made from a derived field rather than an intrinsic one?

Specifically, I'm having an issue creating an axis-aligned slice using the
divergence of the velocity field. It's taking around 6.5 minutes just to
make the slice, whereas if I use temperature or density, it takes around 10
seconds or so for the same dataset.

I also notice that the amount of time it takes is not dependent on the
number of processors I'm using. I've used 1, 12, and 24 processors, with
identical results, even though I'm calling enable_parallelism(), and I can
see that all the processes are running.

I read in the docs that slice operations aren't generally done in parallel,
but in this case it seems that maybe it would be beneficial. A similar
operation in VisIt completes much faster, so I'm wondering if I've
misconfigured something, or if there is something I can do to speed things
up.

I'd appreciate any thoughts anyone has on the subject.

Thanks,

Dan
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