Preview generation performance in LightRoom

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  • Updated 3 years ago
  • (Edited)
I'm often struck by how long Preview generation takes. On a brand new, top of the line MacBookPro with DNG images on SSD drives, LR takes up only 18% CPU utilization while generating previews. Last night I tried to generate previews on a folder with lots of images and it only got through 20% of them over 12 hours. I notice that the additional threads aren't being utilized at all which means this process isn't multithreaded is it?

This problem is compounded because there are poor controls for managing previews on large catalogs. When the Previews file gets above 100GB we're forced to throw it away and start generating new previews on just the pertinent images (potentially with different settings - 'low' quality for example saves a lot of space and is visually acceptable). I wish previews would expire after a period of inactivity just as 1:1 previews do. Some of my catalogs are 8 years old...

So I'm wondering 1) what can be done to improve the performance of preview generation and 2) what can be done to improve previews management.

p.s. on a similiar note, I'd love to see DNG Conversion multithreaded in LR. Demanding pros need performance!
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Scott Martin

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Posted 3 years ago

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Simon Chen, Principal Computer Scientist

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Where are the source raws located? On the same fast SSD or on some slower NAS/external drive? If it is the later, that could explain the lower CPU usage by Lr, because Lr is blocking most of the time waiting for the disk i/o to complete. When the negatives are loaded, the preview rendering could use up to 1/2 of the available physical cores on your machine. That number is reported by the "Maximum thread count used by Camera Raw" number in Lightroom's system info dialog.
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Scott Martin

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Hey Simon - thanks for your response! Off the SSD it's bad and even worse off an external RAID. Would be nice to see this performance at least double if it were multithreaded and utilized all the available threads... Could it not also be made to generate several previews in parallel?
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Simon Chen, Principal Computer Scientist

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On speeding up theĀ DNG Conversion, you could consider batching a couple (or more depending on your system configuration) DNG conversion tasks in parallel. That could allow you to squeeze more juice out of your capable hardware. It would be an option if you are not doing interactive work in Lightroom during conversion.
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Steve Sprengel, Champion

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Or just not use DNGs.
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Scott Martin

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No way Steve. I'd rather have the performance hit upfront than later down the line. The file size savings, embedded metadata, decreased backup times, and file verification all make it worthwhile for me. I *want* the DNG workflow to work and that's why I'm pointing out these shortcomings.
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Simon Chen, Principal Computer Scientist

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I hear you Scott. We made a change in Lightroom 6 to allow export taking advantages of multiple cores on capable machines (>=4 cores), the same techniques that are used in the DNG Converter. We hear customers who loves the speed up and we also hear customers who want Lightroom to be interactively more responsive while an export session is running. It is certainly a tradeoff that we have to be mindful.
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Scott Martin

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I think high volume pros would always vote for speed. Thanks for your perspective Simon!
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Orin Zyvan

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I would like to throw in a second request for a faster performing Lightroom when it comes to preview generation and many other features which could benefit from being multi threaded. It would be much appreciated if Lightroom took advantage of my 12 core threaded Mac Pro!
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eartho

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Preview generation has always been extremely slow and i'm not sure Adobe has ever understood what users are asking for.

The sad thing is, there's an option on import that could give us what we want, but it's never been implemented correctly... Embedded and Sidecar.
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Scott Martin

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Earth, can you tell us more about this? Why do you use this option, how does it appear to misbehave, and how would you like it to perform?