Rendering paused hours after calculating final gather 99% - solved (hope so)

[3d-labor]

After a long time I again had the same error as described earlier:
I had a problem with one scene where the rendering process stops during final gather calculation. The "Computing final gather points"-bar shows 99,9% and the rendering process stops for several hours (but processor worked between 10 and 15%, not idle), but then it goes on with rendering and ends. Or stopped completely sometimes.

One answer of the forum was, that it could be a Vray issue, but I render with MentalRay (next time I should be more precise).

Now I read the Manual of Forest Pack once more and found the hint, to enable "Use placeholder objects" (Render setup-->Processing-->Translater Options). It seems, that this was my problem. In one scene accidentally this option was not marked. After that I saw, that the memory consumption was only 5,6 GB vs. 15,3 GB before that. May be that my 16GB render machine stopped because of that, but the system panel showed now swapping. And during the render process the processor load is constant 100% all the time (in my investigations before that with a very small render region the processor operated between 10-15%).

Didn´t know how important this "small" adjustment "Use placeholder objects" can be. 

[iToo]

Glad the problem is solved. Thanks for letting us know, this information may be useful for othe users.

This is the description for "Use placeholder objects", copied from the Max documentation:

When on, 3ds Max sends geometry to the mental ray renderer only on demand. Initially, the mental ray scene database is populated only with the sizes (bounding box) and positions of objects in the 3ds Max scene. An object's geometry is sent to the rendering engine only when mental ray renders a bucket that contains the object. Default=off.

This option can improve rendering speed when a large amount of the scene's geometry is outside of the view you are rendering.

When the mental ray renderer is low on memory, Use Placeholder Objects enables it to increase available memory by deleting object geometry from the scene database. This can dramatically reduce memory usage, but at a possible cost in rendering speed.

Although theorically this option should not be required rendering instanced objects (since only one copy of the geometry is stored in memory), we found from our tests that it has a great impact on render performance.