Lightroom slow "saving metadata" when opening a PSD in Photoshop

Thanks a bunch, John. You've explained it well (and patiently). 

"So, Automatically Write Changes Into XMP won’t create sidecars for anything but proprietary RAW files? It won’t cause them to be created for PSDs and DNGs?"

Right. LR writes metadata to .xmp sidecars for proprietary raws and .heic photos.  For all other still-image formats, including DNG and PSDs, it writes the metadata into the files themselves. For videos, it doesn't write the metadata back to the files or to sidecars.

"If that’s the case, does "Automatically" mean it will save any metadata changes at the time those changes are made, rather than waiting until I’m opening the PSD or DNG in Photoshop?"

That's right, the changes get saved back to the file quietly in background while you continue to use LR interactively. Usually that happens nearly instantaneously, though if you've just made metadata changes to a large batch of photos or a first-time metadata change to a PSD, it might take a few seconds; but you don't have to worry when it completes -- LR will keep track of that.

So suppose you have a PSD that you've just labeled red. In background, LR starts updating the PSD's metadata, which as discussed before, might take 5-15 seconds if the PSD is very large and this is the first time you've changed its metadata. But you don't notice that, and you keep working in LR.  Minutes or hours later, you edit the PSD in PS, and it opens very quickly, because LR has already written the metadata change to it.

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You wrote "LR stores the XMP metadata inside the DNG files (and all non-raw formats except HEIC) rather than in sidecars."

So, Automatically Write Changes Into XMP won’t create sidecars for anything but proprietary RAW files? It won’t cause them to be created for PSDs and DNGs?

If that’s the case, does "Automatically" mean it will save any metadata changes at the time those changes are made, rather than waiting until I’m opening the PSD or DNG in Photoshop?

Regards,
Russell

Automatically Write Changes Into XMP might have slowed down interactive use a very long time ago, but at least since LR 4, it's very unobtrusive with respect to interactive use of LR.

It has some advantages: It's a last-ditch backup mechanism in case your normal catalog backups fail. (And unless you test your backups every month, every IT manager knows it's very possible your backups will fail at some point.) And if you accidentally delete some photos from your catalog, you can recover the photos from Trash or your backup system, reimport them, and get back your edits and metadata changes (which may not have been captured by your most recent catalog backups).

It does have a cost: If you do a bulk metadata change, such as renaming a keyword, all the affected .xmp files and non-raw files (e.g. PSDs, TIFFs, JPEGs) will get modified, causing your backup system to back them up again.  Not a big deal for many, but some people don't like that.

With respect to DNG: LR stores the XMP metadata inside the DNG files (and all non-raw formats except HEIC) rather than in sidecars.

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Thanks for the quick ad helpful response, John.

It looks like "Automatically Write Changes Into XMP" causes it to create the sidecar files, which many "experts" say slows LR down when editing. And others say you should Automatically Write Changes Into XMP. 

Since I don’t edit PSDs in LR, other than the metadata that’s causing my problem, it would be great if I could set LR to only write to XMP for PSDs. I convert all my raw files to DNG on import, so it would be making sidecars (and writing to them) for every DNG in the catalog, right? I guess I’ll just test both way and see what happens.

"but I do sometimes flag or set a color label. Is Lightroom copying the metadata from its database into the PSD?"

Yes. Whenever you do Photo > Edit In, if there is any metadata changes in the catalog that haven't been saved to disk, LR will first save the metadata to the file before opening Photoshop, ensuring that Photoshop has access to that metadata. (Color labels are stored in file metadata, but flags are not.)

The PSD format isn't particularly amenable to fast saving of metadata. When LR saves a color label back to the file metadata, it must first rewrite the entire PSD to make room for the label. If you subsequently change the label, there will usually be room for LR to overwrite that label, rather than having to rewrite the entire file.

If the PSD is very large, it can take many seconds to rewrite the entire PSD (just to save a three-character label!).  This is exacerbated if the file is stored on a slower disk.

You can see the effect: Start with a very large PSD (e.g. 1.5 GB) newly imported into LR. In LR, do Edit In Photoshop and observe there's no Saving Metadata. Close the file in PS. In LR, change the label color to Red and do Edit In Photoshop; observe that Saving Metadata takes many seconds. Exit PS. Change the label color to Green and do Edit In Photoshop; observe that Saving Metadata now goes very fast.

There are two ways to avoid this delay:

- Set the option Catalog Settings > Metadata > Automatically Write Changes Into XMP. This will do the metadata saving in background soon after you make any metadata change (e.g. set a color label).  Thus, most of the time when you Edit In, the color label will have been already saved to the PSD and you won't have to wait.

- Use collections rather than color labels. Collections don't get saved in metadata.

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