# Reading edits and updating thumbnails



## stevemoorevale (Jan 18, 2020)

Hi again. 

Not an issue as such but was wondering why it is that when i open an old folder of photos lightroom displays the thumbnails of the original unedited raws and then works through reapplying edits and updating the thumbnails on the fly. Shouldn't the thumbnails already be up to date? Am i missing a menu option that needs to be ticked?


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## Johan Elzenga (Jan 18, 2020)

No, you are not missing a menu option. There can be many reasons why old thumbnails are no longer up-to-date, including possibly that Lightroom is simply wrong about that.


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## Califdan (Jan 19, 2020)

LR will jettison previews that have not been used in a long time.  I have not seen documents specifying their rules for so doing but it seems to not be uncommon for previews not accessed in several month to be removed.


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## Johan Elzenga (Jan 19, 2020)

Califdan said:


> LR will jettison previews that have not been used in a long time.  I have not seen documents specifying their rules for so doing but it seems to not be uncommon for previews not accessed in several month to be removed.


There are no rules because I don’t think Lightroom is supposed to do that. It is only supposed to delete 1:1 previews after a certain time (if you checked that option in the preferences). But in reality it does indeed seem to happen sometimes.


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## Califdan (Jan 19, 2020)

Undocumented feature?


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## Victoria Bampton (Jan 19, 2020)

Califdan said:


> Undocumented feature?


That's code for bug!


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## Califdan (Jan 21, 2020)

Actually, given LR's ability to re-generate previews of the needed size as needed, I'd would expect it to jettison ones that haven't been used in a long while.  However, I would also expect there to be a preference setting where I could tell it not to remove previews  and if I allow it to, a preference where I can provide  some parameters as to when it does so.  E.g. clear previews older than xx months,  and clear oldest unused previews when the previews folder exceeds x mgb.


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## Johan Elzenga (Jan 21, 2020)

Califdan said:


> Actually, given LR's ability to re-generate previews of the needed size as needed, I'd would expect it to jettison ones that haven't been used in a long while.


It does not (or should not). That is why previews.lrdata can become so huge.


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## clee01l (Jan 21, 2020)

Johan Elzenga said:


> It does not (or should not). That is why previews.lrdata can become so huge.


I'm not so sure that it "Should not".   It might be worth a Feature Request.  Periodically, when my Previews folder gets "long of tooth" and fat, I will delete the folder to force LR Classic to build a new one.  I will then go into LR Classic and rebuild selected previews when LR is going to be idle anyway.


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## Johan Elzenga (Jan 21, 2020)

clee01l said:


> I'm not so sure that it "Should not". It might be worth a Feature Request.


'Should not' meaning that AFAIK it isn't supposed to happen right now. Not that it might not a good idea. It might indeed be a good idea in order to keep the preview.lrdata a reasonable size.


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## Califdan (Jan 22, 2020)

With absolutely no inside info,  I suspect they programmed it to trim un-referenced previews from the folder after some period of time but never bothered to tell anyone they were doing so.  Possibly they figured that no one would notice or care since it rebuilds them when needed.    I first figured out that older previews were being jettisoned when I was on a long airplane flight and figured it was a good time to do some keyword work on images in historic folders from years ago knowing the keyword work does not require use of the actual image file which were not with me on the plane.  It was then I discovered that all the previews from my many years old image folders were no longer present even though I had never cleared my previews folder or in any way asked LR to remove old previews.  

I think it's a good thing to keep the Previews folder form growing to the size of Texas, but they should give us some preferences to manage the pruning parameters.


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## Johan Elzenga (Jan 22, 2020)

Califdan said:


> With absolutely no inside info, I suspect they programmed it to trim un-referenced previews from the folder after some period of time but never bothered to tell anyone they were doing so.


Un-referenced, meaning 'missing' previews, yes that may be the case. But I don't think they trim 'unused' previews. Your previews.lrdata can become very large, which suggests that they are not deleted at some point. I had 250 GB previews at some point. Another reason why I don't think it happens like that is what the OP observed. He observed that the previews were there, but not up-to-date. If you delete the previews.lrdata, then you will see that the thumbnails are initially missing altogether. Anyway, it doesn't really matter if this is deliberate or a bug.


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## Califdan (Jan 22, 2020)

Johan Elzenga said:


> Un-referenced, meaning 'missing' previews,



Unreferenced meaning that LR has not referenced (i.e. needed)  the preview in a long time.   In other words, images that haven't appeared in the grid or filmstrip in a long time.


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## Johan Elzenga (Jan 23, 2020)

Califdan said:


> Unreferenced meaning that LR has not referenced (i.e. needed)  the preview in a long time.   In other words, images that haven't appeared in the grid or filmstrip in a long time.


OK, like I said, I don't believe this is true. If it were ture, then the previews.lrdata would not grow to such monstrous proportions. Nobody looks at 200,000 images regularly, but quite a few people have a catalog that contain that number of images. Many if not most images will be 'unreferenced' in that case, but still the previews.lrdata can become very large and will keep growing. It wouldn't if the previews were regularly trimmed.


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## Johan Elzenga (Jan 23, 2020)

BTW, it also doesn't make a lot of sense that Adobe *did* add an option  in the preferences to discard 1:1 previews after a certain time, but *no* option to do the same with standard-sized previews, even though that was happening without the user's knowledge or consent.


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## Califdan (Jan 23, 2020)

Johan Elzenga said:


> BTW, it also doesn't make a lot of sense that Adobe *did* add an option  in the preferences to discard 1:1 previews after a certain time, but *no* option to do the same with standard-sized previews, even though that was happening without the user's knowledge or consent.


I agree with that statement.  

On your comment about 200,000 previews,  I think it would depend on the algorithm they used (if they do it at all),   But, I could see where someone could just click through a bunch of ancient folders or access collections containing images from ancient folders etc.  And, if the algorithm purged ones not used in, say 365 days I could see that 200,000 could be there.  

I'm basing my suspicion on my own experience which I alluded to above.  In my earlier days of LR I had yet to learn about the previews folder and as such had never deleted the previews folder  or any of its contents.  I also have always imported with either full or minimal previews.  As such, 100% of my images should have had previews at that time.   But, when I took my catalog on an airplane flight (copied entire catalog folder to laptop) without my external images drive, a good half of the images had no previews and these were typically the oldest images.   So,  I surmised that Adobe pruned them using some intenal criteria.   Since then I have not done any experimentation, but it sill seems that from time to time LR has to re-build previews for images that should by all rights still have had a preview.   But, maybe something else is going on as well.


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## Johan Elzenga (Jan 24, 2020)

I think it's a bug. There is a 'root-pixels.db' and a 'previews.db' database inside the previews.lrdata, so maybe something in there gets cut-off or maybe it has a maximum number of lines where it shouldn't. That would explain why preview can get lost, without the previews.lrdata getting smaller.


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