[mythtv-users] Excessive disk usage in remotecache on Raspberry Pi

[Michael T. Dean]

On 12/02/2016 11:16 AM, Peter Bennett wrote:
> One of my raspberry Pi's started acting strangely a few days ago and I
> found it had run out of disk space.
>
> The raspberry Pi disk is an 8 GB SD card.
>
> I found that the directory ~/.mythtv/cache/remotecache was using 1.2 GB.
> On a normal frontend this may not be an issue but on a Raspberry Pi with
> only 8 GB available this can be a problem. This directory has many files
> with names like 3707_20161124170000.ts.png.
>
> Can anybody tell me if this directory ever gets cleaned up by the system
> or will it go on increasing forever. Do those files get deleted when the
> relevant recording is deleted?

No.  No one has yet implemented any cleanup there.  Users can 
(occasionally/at shutdown/before startup/...) delete the 
~/.mythtv/remotecache directory as desired (as well as any other cache 
in ~/.mythtv, including themecache, thumbcache, and Cache-*). The only 
downside to doing so is that any images required during running will 
have to be transferred (and scaled/...) when needed.

Remember that any automatic cleanup would have to consider that there's 
potentially a copy on each frontend-running system.  So, event-based 
(such as on-delete) cleanup would require messages to all running 
frontends--and would miss any disconnected/not-running frontends.  Also, 
determining that the image is no longer necessary/used is very 
difficult, especially for metadata images (some of which are used by any 
episode of the series, or for episodes that don't have any specific 
image, or ...).

For a resource-constrained device like the pi, you could just clean it 
up in a shell script using find...

find ~/.mythtv/remotecache -atime +7 -delete

to delete any that haven't been accessed in the last 7 days, or whatever 
you like.  Put this in the startup or shutdown script for mythfrontend 
and it's semi-automatic.

I'd actually suggest a similar type approach if you want to automate it 
(but not using find).  You could run a task in the frontend HouseKeeper 
that deletes any remotecache images that haven't been accessed in the 
last month or so?  Ideally you'd pick a number that just works for 
people, rather than having a setting to adjust it--and since you're 
using one of the most-resource-constrained devices, you should be able 
to find an appropriate value.  (FWIW, I don't know if Qt has a way to 
find a file's access times--it may not since not all file systems 
support ctime/mtime/atime--but if nothing else, you can use C/C++ code.)

Mike