A volume with two lights plus emissive objects. Without light AOV's, renders in about 20 minutes, with them in about 8 hours. RAM isn't capped. Anybody knows what might cause that, or how to avoid it?

That's news to me. I haven't seen a difference in performance. Is this with LPE tags or oldschool light breakouts?

Just the "Combined Lighting (Per-Light)" and "Combined Emission" image plane presets. No tags.

I havent seen that with lights
but I noticed something similar with Emission AOVs and volumes, not sure if that's your case
since emission AOVs by default are Full Opacity Sampling and that for some reason slows down rendertime when rendered together with lit density
rendering density and emission separately is fast even when emitssion render is held out by density, I didnt have time to investigate why, but this is in 18.5

Yes I did have an emission AOV. Thank you, I'll try rendering just that separately. And this was in 19.0.498.

Tanto
Yes I did have an emission AOV. Thank you, I'll try rendering just that separately. And this was in 19.0.498.

I mean quick try would be to change emission aovs from Full Opacity Filtering to Opacity Filtering but that would use stochastic sampling and may be grainier, however if it speeds up you'll know your culprit
rendering separately was fast for me for emissive volumes even without stochastic sampling

tamte
I mean quick try would be to change emission aovs from Full Opacity Filtering to Opacity Filtering but that would use stochastic sampling and may be grainier

That did the trick. Thanks tamte!

tamte

Tanto
Yes I did have an emission AOV. Thank you, I'll try rendering just that separately. And this was in 19.0.498.

I mean quick try would be to change emission aovs from Full Opacity Filtering to Opacity Filtering but that would use stochastic sampling and may be grainier, however if it speeds up you'll know your culprit
rendering separately was fast for me for emissive volumes even without stochastic sampling

Tanto
Just the "Combined Lighting (Per-Light)" and "Combined Emission" image plane presets. No tags.

Combined emission is a no-no. It should never be used with volume rendering as the direct component requires full opacity samples for quality, and the indirect component should be done with screendoor samples for performance.

Using the combined plane requires a compromise.

jsmack
Combined emission is a no-no. It should never be used with volume rendering as the direct component requires full opacity samples for quality, and the indirect component should be done with screendoor samples for performance.

ah, that makes sense
so having direct_emission at Full Opacity Sampling
and indirect_emission at Opacity Sampling
should work fine and in fact that seems to be the default for those AOVs

Thanks to you both. Was trying to have identical AOVs for comp as renders from another software, but this certainly argues for separate direct and indirect AOVs in these cases, maybe combining them in a post-process.