Purging Cache

GA
Posted By
George_Austin
Jun 7, 2004
Views
539
Replies
8
Status
Closed
In the PSCS browser, what is the differebce between "Purge Cache" and "Purge Entire Cache"?

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IL
Ian_Lyons
Jun 7, 2004
File Browser generates a cache for each individual folder and sub folder. However, this cache is only built when the folder/sub folder is selected.

Purge Cache deletes the cache associated with the selected folder/sub folder and ignores the rest.

Purge Entire Cache deletes the cache for all folders and sub folders.

When you delete a cache it will need to be rebuilt next time you select the folder/sub folder.

When you move or rename a folder/sub folder the cache for that folder/sub folder must be rebuilt. This can a real drag. You can minimise the effects of this by exporting the cache after it is built. Doing so places 3 files inside each folder/sub folder. FB will use this local cache if available and so has the potential to save a significant amount of time rebuilding the full cache. If you’re in the habit of moving or renaming folders/sub folders it would be wise to use the Export Cache command.

Ian
GA
George_Austin
Jun 7, 2004
Thank you, Ian, that helps.

I experimented with a new small sub-folder containing only 4 unedited images and not having those three "local cache" files. I purged its cache and immediately exported the purged cache. The three files then showed up in the sub-folder: P8M 4kb, P8P 540kb, and PST 14kb. And a fourth file "Thumbs.db" 12 kb also appeared

Since the cache had been purged (presumably empty), what could possibly have filled the P8P file with more than half-a-megabyte?

George
GA
George_Austin
Jun 7, 2004
Another puzzling scenario:

I flag some files in a sub-folder, purge that folder’s cache, shut down PS, turn off the computer, reboot, reactivate PS, and bring up the folder. The flags are still present on the files I flagged even though I purged the cache containing the flagged data. So the flag data is part of the folder, cache notwithstanding. Now I move the whole subfolder to another folder. The flags are gone. What gives?

George
IL
Ian_Lyons
Jun 7, 2004
George,

It’s easier to explain what’s happening than answer your quesions directly. It’s also possible that my earlier post was not as clear as it should have been.

When you Export the Cache you are creating a localised STATIC version of the cache for the selected folder (i.e. it doesn’t update when new files are added or old changed). This static version is created at a point in time from the data making up the DYNAMIC cache stored in the folder named "Documents and Settings/………/Application Data/Adobe/File Browser/PhotoshopCS".

The dynamic cache is being updated on a continual basis. When you Purge the Cache you are deleting only the dynamic version for the selected folder. When you choose "Purge the Entire Cache" ALL of the dynamic cache files are deleted, but the static versions (if present) will again remain.

The static cache will be stored in the form of three files (AdobeP8M, AdobeP8M and AdobeP8T) in the same folder as the images. Therefore all the data associated with the images within the folder that existed when this cache was originally created will be retained (possibly the answer to your Question in post 3 about the Flag info being retained). This data includes: the Preview Images (each can be quite large – answer to your Question in post 2), Flags and a bunch of other important information. Photoshop will use this local static cache as the starting point for a new dynamic cache but will only begin building it when the folder is selected.

As I mentioned above moving or renaming a folder will mean that Photoshop needs to rebuild a new dynamic cache for that folder.

There are arguments for and against exporting the cache. As you’ve already observed it will further increase the amount of HD space used, but it does this in the form of providing you with a backup of the dynamic cache. Having this backup can substantially reduce the time needed to rebuild the dynamic cache and once it is rebuilt it’s simply a matter of exporting it again thus updating the static cache. Even better is the folder mobility and naming flexibility that having a local cache offers. This brings me to a "Gotcha"

When you choose "Build cache for sub folders" don’t be suckered into thinking that you can simply follow it up by choosing "Export the cache". If you do all that happens is that the three files associated with the parent folder will be exported. If there were images in that folder then the static cache will have the data for them, but there will be NO static cache exported to the sub folders. Whether this is how it is meant to be is a matter for Adobe to explain.

Finally, if you really want to understand what’s going on in FB then you’ll need to get hold of material by Bruce Fraser, Jeff Schewe or Seth Resnick. I’m sure there others but these three guys between them know pretty much everything that the engineers are prepared to tell, and then some 😉

Ian
GA
George_Austin
Jun 7, 2004
Ian,

I am really much obliged for your detailed answer.

Last week, clearing leaves and debris from behind a brick wall in my backyard, I encountered a swarm of bees in a very nasty mood. I was stung a dozen times. Had an excrutiating allergic reaction—full body itching and burning and acute shortness of breath and was whisked to the nearest ER.

I think I’ve unearthed another beehive! 🙂 🙂
George
IL
Ian_Lyons
Jun 7, 2004
George,

It’s a beehive alright!

BTW: the terms Static and Dynamic are not mine. I can’t recall exactly who used them in the context of File Browser caches – it might have been material by Bruce Fraser.

Ian

PS: next time hire someone in to clear up the yard 😉
GA
George_Austin
Jun 9, 2004
Ian

The cache file designators M, P, T mean what? I’m guessing M holds meta data. T holds thumbnail data, and P holds ???

Since static and dynamic caches can exist for the same folder at the same time and they can differ, would you say the static cache has priority? How are differences between them resolved?

George
IL
Ian_Lyons
Jun 9, 2004
George,

The static cache is only used in the event that CS cannot find the dynamic cache. As I understand it It will use it as the start point for rebuilding the dynamic cache.

I think you’ll find that P = Previews I wouldn’t like to say one way another what T and M are used for.

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