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AppCleaner
The AppCleaner is responsible for expendable files that can be attribuetd to a specific installed application. Files that are expedendable should fullfil the following criteria:
- App automatically recreates them if necessary
- Deleting them does not cause errors within an app
- No user created information is lost (e.g. a picture taken with the camera is "user created").
This generally includes all official cache locations (i.e. /data/data/<pkg>/cache/ and /<sdcard>/Android/data/<pkg>/cache/) as well as uncommon cache locations (due to non-standard directory naming or location) and specific directories that have been manually added to SD Maids databases.
The AppCleaner works on a per App basis, meaning that any file it checks is related to a known installed app. This is in contrast to the SystemCleaner which is generally unaware of any app<->file relation.
Unless you are really low on free space it's generally not beneficial empty all your app caches every day. It's not harmful to your device or apps though. Low free space can negatively impact device performance, but this only happens below 10% or less (varies with storage) free space. Above it you would gain better performance by keeping a moderate file cache.
Imagine an email app, its great to have fast access to some mails, but the cache also contains things like pictures from 3 day old emails. Now be honest how often do you really go back to view a few days old content? In most cases I'd rather have more free space and let the app just re-cache the files when they are needed. Additionally some of the cache files might already be stale now and would have to be reloaded anyways or not at all.
Some apps create ridiculous amounts of files in their cache folders, some during normal operations, some because of bugs. Large amounts of small files can negatively impact app performance as traversing all these files costs time. There are cases where apps use buggy analytics software that causes them to never transmit and or delete their analytics files, leading to over ~50.000 files to accumulate and slowing down the app (through the slowed down analytics software). It's also possible that apps screwed app their own cache management and start to display wrong files or fail to load, clearing their cache might help and is often less effort than reinstalling the app and setting it up again.
- Include System-Apps: Whether system apps should be included in the results.
- Sort mode: How the results should be sorted.
- Minimum cache age: SD Maid can filter out files that are below a minimum cache age (in days). Note that SD Maid can not enforce this for all files on unrooted devices. See FAQ on why some exclusions don't work.
- Skip running apps: Skip currently running apps. If running apps are not skipped they are killed before deleting their cache.
- Show inaccessible items: Some items, especially on 6.0+ without root may be known to SD Maid, but can't be accessed (i.e. deleted).
First lets get something straight: Caches are not a bad thing. Loading files from cache instead of downloading or recalculating them again can make loading faster and save device resources (battery/cpu/bandwidth).
In a perfect app world, all apps manage their cache perfectly and a tool such as this would be unnecessary. But the world isn't perfect and apps missmanage their cache by e.g. not limiting it's size. Often the user is given no control over it except for wiping the whole cache. The AppCleaner aims to provide the user with detailed information and more fine grained control over each apps cache.
The systems cache clearing routines only cover the default caches. This means files that within the official cache folder in the official app data locations (e.g. /data/data/<pkg>/cache and <sdcard>/Android/data/<pkg>/cache).
But apps may also create directories and files on the root of the sdcard and save their cache in those directories or use weird constelations such .cache or /files/cache.
The AppCleaner deletes individual application caches. Clearing cache via recovery wipes the /cache partition which is unrelated to app caches and contains system.
On older Android versions (around 2.3?) the cache partition was heavily used to store temporary files when downloading an app through the Android Market. Today it's not that much in use on a daily base. AFAIK some built in backup code uses it, as well as recovery and OTA updates, though there is much variance between ROMs. In essence is not used by normal apps due to special permissions being required to access it.
The AppCleaner differs slightly between rooted and unrooted device. The cleanable amount is roughly the same, but unrooted devices can't clean some files individually, meaning that to remove certain files, you have to press the "Delete all" button. This is necessary because without root we have to abuse a hidden system function called freeStorageAndNotify which tricks the system into running it's own cache routine which deletes the official private app caches we can't access on unrooted devices.
This is means that you can still click an entry and it will clean just that app, but there might be additional files belonging to this app that can only be removed if you use the 'clean all' routine. Such entries are labeled with an extra and icon and will also display "20+? Elements" (this entry has 20 files/folders plus an unknown amount of extra items). It's unfortunately the only way to achieve this without the luxury of root as we can't access the files directly, but instead have to ask the system for this information and this is all the information/options we get.
The aforementioned freeStorageAndNotify is no longer available since Android 6.0. This means that SD Maid is no longer able to use this trick to clear private app cache on unrooted devices. SD Maid will still process caches on public storage. A lot of other "cache cleaner" app are not aware of this change in Android 6.0 and act like they still work, but on further investigation nothing is deleted. This also breaks many other apps that solely relied on this trick to for file deletion (even on public storage that is accessible).
If you are using the AppCleaner on an unrooted device, you may have noticed that despite creating an exclusion for a specific app, it is still part of the scan results. This happens because we have to use the freeStorageAndNotify trick to delete the private cache files. Using this trick means that not SD Maid, but the system itself does the deletion and the system does not know about SD Maids exclusions. Since SD Maid v4.2.0+ freeStorageAndNotify can be turned off in the settings.