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Thursday, May 29, 2014

Houdini - Explicit Cache

Classical Scenario:
You deadline is today at 7pm. Which means your deadline really is tomorrow around 9pm ! You've time to recalculate your huge flip sim that takes about 13 hours to complete (note, not 12 hours, not 14...13 the evil number). Each bgeo file is about 666mb. You hope you'll have enough HD space, but hey ... HD space is never enough ! Even Confucius knew this.
So you cross your fingers, and hit "Render" on your rop_geometry network to start your 999 frames FLIP sim.

Now usually, when you've only one chance to do it right and if you miss it you'll be fired, usually this is what happens in order:
1 - you run out of HD space on the frame 998.
2 - Linux crashes for the first time in 12 years
3 - Houdini crashes for the 13th time in 2 hours
4 - power outage in the whole <city where you are in that moment>

You better remember that one of these 4 things (if not all of them) will happen. It's important to be positive.

How will our fellow FX Artist save his job, and manage to pay the rent of his mansion with pool in the Hollywood Hills ?

The answer is this gorgeous little gem of pure love called "explicit cache" and his little friend "explicit frames to cache" on the DOP Network node.



This option is off by default, cause the files generated can fill your 12Tb HD very quickly.
But this is where the second option comes really in handy !
You don't have to save ALL the .sim files for each one of your 999 frames of simulation.
You can save the last, say, 5 (or less maybe) and restart the sim from the smallest frame number in your cache ! This way you'll not clog your HD with unnecessary GIGANTIC .sim files, and you'll still be able to resume your sim.

Example:
n.4 happened. And I managed to simulate only 362 frames of my 999 frames sim. But I was wise enough to enable the explicit cache option and specify a frame history of 5.
So, if I go in my ...../simcache directory I'll see these 5 files:


What I usually do is delete the last one. Why ? Well ... I love Houdini, but I will never trust that he managed to write out the last sim file while the power of my computer was off. And you've a pretty good clue of this checking the file size of the files. They are all ~153 Mb, apart from the last one ! MM ... suspicious. Delete !



Perfect. Now you have 4 cache files and you're sure they are fully functional.

Now you can restart your sim starting from the frame 358 and Houdini will seamlessly continue simming like if you started from frame 1.


This saved my <censored> several times already.



2 comments :

  1. in your scenario, any reason you didn't restart at frame 361 ?

    ReplyDelete