[mythtv-users] Are there any throttling features in Mythtv?

[Mike Perkins]

Brad DerManouelian wrote:
> On Feb 3, 2009, at 8:01 AM, Mike Perkins wrote:
> 
>> Sunday evening, we sat down to watch a film I'd recorded just before 
>> Christmas, 2 hours long. This was about 7:45 pm. An hour and a half 
>> later, the whole system hung. There was not the slightest sign that 
>> anything was wrong up to the point it froze.
>>
>> After some investigation of the front end[1] I discovered that the 
>> back end had hung. This was because at 8:55 pm the back end had begun 
>> three simultaneous recordings on three DVB-T tuners. Apparently my 
>> back end couldn't cope with reading and writing four streams 
>> simultaneously[2].
>>
>> Now, before you all scream "throw more hardware at it!" I would like 
>> to point out that whatever system you've got, a point will come when 
>> you are likely to stress it. So it occurred to me to wonder if there 
>> was any kind of throttling or warning available in mythtv, apart from 
>> "max # of jobs to run on this backend".
>>
>> For example, if I were to play a long film that happened to overlap a 
>> period of heavy recording, would it be possible for the system to say 
>> something like "this probably isn't a good idea, go and watch 
>> something shorter"? Or for it to show me what's likely to happen 
>> within the playing time of the selected program?
>>
>> I wouldn't want to go as far as rescheduling, but some kind of 
>> information screen might be useful. At the moment, to find out what's 
>> scheduled involves going into "schedule programs" then "upcoming 
>> recordings" to see a list, then backing out and going to "watch 
>> recordings" to find something to watch. Anyone any suggestions?
>>
>> [1] see separate post. The front end was ok in this instance.
>> [2] recording three simultaneous streams is known to work ok. 
>> Recording 2 streams and watching one is known to work ok.
> 
> When I add tuners, I always set them all to record to make sure my 
> system can handle it. It's possible for me to record 8 things at the 
> same time. My system doesn't fall down when it happens (never happened 
> naturally, only when I forced it to happen). How is mythtv supposed to 
> know that your system can't handle 3, but mine can handle 8 and at what 
> point will my system not be able to handle any more? I haven't found my 
> limit.
> 
Yup, did that, see [2] above. In fact, the system lasted 16 minutes with three 
recording and one playing before it quit. How long a test do you suggest I make? 
Fortunately all the recorded streams in question were able to be re-recorded, so 
nothing [in this case] was lost. What happens when you can't re-record something?

I know nothing is likely to be done to assist my particular circumstances. I 
just want to point out that it can happen to anyone, and might there be some 
method of reducing the impact, or even making sure it can't happen. I wanted to 
get people thinking.

As for how is mythtv supposed to know that my system can't handle 3 (actually 
4), but your can handle > 8, that's straightforward. Have a limit such that # of 
input + # of output streams <= # of tuners as a default, with it being a backend 
setup field that can be adjusted by the user as experience of the system 
improves. Again, just a thought idea.

-- 

Mike Perkins