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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.

Warning

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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Alternatively, you could set the interval to 300s and the renderer will update the image approximately every five minutes after it starts work on the frame. This time includes the renderer startup time, such as parsing RIB, cracking procedurals, and building ray tracing acceleration structures. As a result, there may be fewer increments before the first checkpoint than between later checkpoints. For convenience, the time-based interval can also be specified with a suffix suffixes of s, m, h, or d for seconds, minutes, hours, and days respectively and these may be combined. For example, intervals of 360s, 6m, 5m60s, and 0.1h are all equivalent. Instead of a suffix, you can also just specify a positive number and time in seconds will be assumed, while a negative number will be interpreted as the number of increments.

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Note that checkpointing is designed for batch rendering to images on disk. Renders to a live framebuffer such as "it" are already updated on-the-fly as the render proceeds. Of the built-in display drivers, currently, only the TIFF and OpenEXR display drivers support checkpointing. You may notice that the files produced include a ~w labeled channel. This is data stored to resume a render from this file.

How to Specify

In RIB, checkpoints can be specified via an Option or by passing the optional -checkpoint argument to prman.

Code Block
prman -checkpoint t[,t]

The above command is seen as the interval given and an optional exit time (the square backets).

You can use several different types of intervals and may be combined:

  • 60s - this is 60 seconds
  • 60m - this is 60 minutes
  • 60h - this is 60 hours
  • 60d - this is 60 days
  • 60i - this is 60 increments (incremental frame rendering, this is ignored if you're rendering to tiles/buckets)

You can combine these as needed, for example: -checkpoint 1h30m would create a checkpoint every hour and 30 minutes

The options for exitat are the same and can even be provided without needed a checkpoint written, in which case you've just told the renderer you want to stop a render and write out the result at a certain time. Below we write out a final result and exit at 30 minutes

Code Block
prman -checkpoint ,30m


It is possible to maintain a checkpointed "final" image using either an .ini setting or a RIB option, with the later overriding the former. If neither is present it defaults to off. When set, this prevents removing the extra channels and the checkpoint tag when writing the final image for the render. The final image will essentially be just another checkpoint, rather than a slimmed down image. This means that once your image has reached the quality you've set and it completes, it can always be restarted by the user later:

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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

Warning

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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