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

[Kevin Kuphal]

On Tue, Feb 3, 2009 at 10:35 AM, Brian Wood <beww at beww.org> wrote:

> On Tuesday 03 February 2009 09:13:18 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.
>
> Other tasks, such as commflagging, transcoding, watching recordings,
> mythfilldatabase etc. will effect your load. Most likely your disk I/O will
> give up the ghost first, at least that's what I discovered. I went with a
> RAID0 array to improve the disk performance, and that helped a lot.


Another quick and common suggest is to keep your database on a separate
drive from your recordings.  There is alot of I/O going to/from the DB
during recordings, commflagging, and playback.

Kevin
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