What does the Preference to "Generate Previews in Parallel" do?

[jbinco]

I cannot find any definition of what this option is doing?  How does this option effect performance?

[John Waller]

https://lightroomguy.com/lightroom-classic-preferences-catalog-settings/

"Preview Generation Settings > Generate Previews in parallel

Set this feature ON

By setting this feature to ON you can speed up the processing of previews during the import process. In this case, Lightroom will attempt to generate more than one preview at a time. In other words, it will try and process multiple previews in parallel rather than sequentially.

This feature works better with computers with more processing cores. Laptop users may want to keep this turned off, especially if the computer starts to really slows down and/or starts to get very hot."

[jbinco]

I appreciate the link and the info.  Now I'm wondering what the source of that person's information was.  I was hoping to find "official" Adobe documentation on this. 

Does this parallel processing continue after the images are imported until all imported images have a new preview? 

Does this parallel processing consume all available physical cores?  Logical cores?

Does this rely on enabling Intel hyperthreading BIOS options?

[TheDigitalDog]

From the "Lightroom Queen FAQ" which is about as close to an official Adobe response there is (and worth getting):

Generate Previews in Parallel

If you have a fast computer, enabling

Preferences > Performance > Generate Previews in Parallel allows multiple previews to be generated concurrently, rather than one at a time. It can, however, have a detrimental effect on interactive performance, so it's best used if you're not going to be using the computer while the previews are building.

[Conrad_C]

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@jbinco wrote:

Does this parallel processing continue after the images are imported until all imported images have a new preview? 

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That probably depends on how you have set up your preview generation in general, which is controlled by other settings.

For example, if you set the Import dialog box to generate any kind of preview on import, then of course preview generation must continue until all are done. But if you’re like me and set it to use embedded previews, then no previews will be generated after import except on demand. That setting is independent of the parallel option, so if you do have the Import dialog set to generate previews for all imports, then the parallel option determines how many cores are allowed to work on that; but if you set Import to embedded previews, then of course the parallel option has nothing to do for imported images and does not apply.

Also, in General preferences there’s an option named “Replace embedded previews with standard previews during idle time.” If that is disabled, then your computer won’t do anything with previews at idle time. If that is enabled, then it will build previews in the background. And again, the parallel processing option modifies how that happens, not whether that happens.

If you are one of the users who wants other applications to have access to more cores while Lightroom Classic is building previews at either import or idle time, then you disable the parallel option.