Hi there,
I am having issues with the secondary GI. Sometimes it takes very long to process it, I’ve notice that if a close MAX and re-open the file it will temporarily fix the problem.
It gets a little annoying when I’m trying to test materials or lighting.
Using Corona 1.4
All the settings on default
Thanks in advance.
Maybe you are running our of RAM?
Are you getting any warnings/errors?
In case you’re using Max2016 then make sure you have SP3 installed. There was a severe memory leak before that.
No warning or errors,
It could be the RAM, I’m actually running 2016
I notice if a close some of the other programs it will go fast and smooth, so I will try with the SP and a RAM upgrade.
Thanks for your replies
I have experienced similar on rare occasions, although speed picked up again 20 seconds after letting it run slow. Never had again since 1.4.
Shot in the dark… But try to type these three commands into the bottom right max script command window.
gc() Garbage Collection.
freescenebitmaps() Cleans up in texture memory.
clearUndoBuffer() Removes your Undo's
Logic being, that in heavy scenes all Undo steps are saved and can add up to gigabytes with heavy changes respecrivly. We may crash past our max’s ram limit and it started paging out parts of max to compesate, which is a classic ruiner of performance.
If this is the case, then undo delete won’t immidietly pickup the speed again, but maybe 10 secs later.
I never had this until 1.4, so far I’ve found two solutions. The first one being merging the problematic scene to a blank Max file, the other one being freeing up tons of space on the HDD I have my virtual memory/swap files on. I don’t entirely get why freeing up virtual memory helps when the scene is using about 3 gigs out of the available 32 gigs of RAM.
Oh and sometimes running Corona Converter and running the Start Conversion, clicking on disabling legacy mode and Coronabmp → Bitmap helps, even though there is nothing to convert 
I’d like to send a scene if this is something else than a memory problem but right now I’m on a tight schedule. Would still be interested in more expert opinions since this can be seriously time consuming. Can it really be the virtual mem?
Just a shot in the dark, since you mentioned 80% ram usage. Paging starts at ~90%
try to disable displacement in the common tab in render settings. maybe something you imported has displacement activated
To be clear it wasn’t me, but the OP who mentioned the ram usage % 
I did tried merging the scene to a blank max, it was fine for a few test renders and then the performance drop again. I will try with the corona converter fix and let you know my findings.
I will try this sounds interesting.
I did, not a change on GI cal.
Thanks for the replies and solutions, will give and update as soon as I try everything.
Just a thought, try rendering the scene with an override neutral Corona Material and see if it changes things. If it does, start excluding materials from the override.
I got my scene to work smoothly again doing this, going through the exclude-list keeping priority on the most complicated materials or the ones that had otherwise questionable setups. It turned out to be my wall material which had some gimmicky bump map combining round corners, composite normal maps and standard bump maps. Once I simplified the bump channel the scene has had no hiccups since.
After several minutes of trial and error I found the issue, a converted proxy, once that I deleted that proxy the performance increased.
Thanks you for the suggestion
Nice to hear you got it solved 
Do you have any idea why this proxy was “corrupted”? Have you tried to reproxy it again and was it ok then? Curious to know why it caused this problem.
I did reproxy the object (It was a tree), but the problem didn’t come back. I don’t know the cause 
Hi, occasionally I have that issue as well and it happens on various scenes, exteriors, interiors proxy\forestpack, displacement containing and not - it happens rather rarely and goes away when I stop that render and do a new one - hard to catch and to pinpoint what exactly is causing it but I’m 99% sure it’s not the insufficient ram problem as I’ve got 64gigs of it and it happens with the scenes eating up no more than 10-25gigs. In my case it does not only slows down uhd calc. phase for at least ±10 times, but it slows down the whole render process too - I remember there were some reports about similar behavior in daily build thread but it seemed that some fix was done in one of the dailies to prevent that, still it does happen occasionally ) The good thing is - it happens rarely and as I’ve wrote above, most of the times goes away on render cancel\stop, rerender.
I am experiencing the same problem here…
I am working with a “heavy scene”, but even after clean it up a lot (from 1.5Gb to 300mb) the crashes continues. And its VERY STRANGE… I had LOW MEMORY warning a lot, after some time working on the scene and doing some region renders or any renders… It smells a lot like garbage in ram… Everytime it crashes, i open Max again, and it renders fine…
And after thinking it´s a Memory problem, i tried to open the scene on a SLOWER machine with HALF RAM (16Gb only) and it renders perfect all the frames 66 frames. No crashes, so it´s not a scene corruption or memory problems...
ON My machine, with 32Gb ram, Windows10, Max 2016, if i do A render Stops it in the middle, do it again, 1 or 2 times, it just crashes to desktop. Sometimes, it locks my computer and have black screen, and i have to reboot. Many Low Ram messages happens before crash sometimes...
;(
So, everytime i need to have get a full render from start to end i need to close Max, open e render. If i stop this render to do something else i need to save it because the crash can happens anytime... If i use Interactive render the crash happens even more often.
Did you try to run MemTest overnight? Might be faulty RAM stick.
Well since the discussion is on going I got to add those symptoms sound very familiar, I have 32 gigs and sometimes the scene is only using like 3 gigs and Corona is giving low RAM warnings and rendering is slow as hell, like first pass taking an hour to clear (just an estimation as I usually cancel after 20 mins) be it PT+UHD or PT+PT. I honestly doubt we are all dealing with faulty RAM sticks, this topic has come up several times before..
I wonder if it could be solely specific to heavy use of Forest Pack since Corona usually starts acting up once I get to the later stages of adding detail with FP. It’s the way Corona doesn’t seem to eat up all the RAM before it slows to crawl that is bugging me, at least with Vray I always got a complete crash once a certain limit was reached