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PRMan has the ability to resume interrupted renders. How this works depends on the mode that it's running in. Non-incremental renders to TIFF and OpenEXR images can always be recovered. Incremental renders to OpenEXR images can also be recovered, but only if the checkpointing option was used.
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When using checkpointing a deep EXR while using adaptive sampling, all of the AOVs considered by the adaptive sampler (e.g., normally the beauty) must be written as well to a shallow EXR. Otherwise, the checkpoint will not be recoverable. |
Checkpointing
Checkpointing is specific to the incremental rendering mode when doing batch rendering. In incremental mode, the renderer makes repeated passes over the image, refining it a bit more with each pass. While the image will be quite noisy during the initial passes, it is usually sufficient to give an impression of how the final image will look.
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Though not strictly atomic, this renaming is done in as small of a window of time as the OS permits in order to avoid mixing new checkpoint files with old. If the renderer is killed or dies for some reason while checkpointing, there may be some .part files left over. Deleting these should safely leave the previous checkpoint intact. Note that looking for these .part files is one way of detecting whether the renderer was killed during a checkpoint. Note too, that this new behavior means that the peak disk space used by checkpointing is now doubled.
Deep Data
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When using checkpointing a deep EXR while using adaptive sampling, all of the AOVs considered by the adaptive sampler (e.g., normally the beauty) must be written as well to a shallow EXR. Otherwise, the checkpoint will not be recoverable. |
We support Deep Data Checkpointing (DDC files) when rendering to Deep EXR formats. When using this feature you will not only see a "shallow" EXR written to disk for each checkpoint but also the DDC, which uses lossless compression, file for recovering the deep data. Since checkpointing often leaves multiple files on disk and deep data can be expensive to store, there is an option to compress the resulting deep data.
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