[mythtv-users] Multiple backends

Raymond Wagner raymond at wagnerrp.com
Sun Mar 20 15:50:39 UTC 2011

On 3/20/2011 07:58, tim draper wrote:
> i have (a fairly power-hungry) mythtv FE/BE machine. this is put into 
> suspend when not in-use. (aka PC1)
> i also have a low powered server that runs 24/7.
> what i'd like todo is build a VM on the server, as a mythtv BE, with 
> the sole purpose of viewing tv listings. this VM would not have a tv 
> card present (not enough PCIe slots) and would rely soly on the data 
> from the PC1 BE

At current, the master backend requires a tuner card.  With no tuner 
card, the backend will shutdown, complaining about a failed sanity check 
in the scheduler.  This is planned to be resolved with 0.25 and the 
rewritten web setup.  Also in planning is breaking out the jobqueue, 
recorder, and scheduler/housekeeper into individual programs rather than 
keep them in a monolithic backend.  With the 
master/scheduler/housekeeper in a separate process, lacking tuners, it 
will be possible to set something up like you suggest, however there 
will still be some stipulations.

The scheduler requires that it know what tuners are actually 
accessible.  When you have slave backends going into standby, the 
scheduler must have ordered it, or it will assume that machine and its 
tuners are unusable.  Similarly, if you restart the process running the 
scheduler, each slave backend must be brought online and reconnected to 
it, so it has a survey of what tuners are available.

Even with recording and the jobqueue (and intensive transcoding and 
commflagging) out of the picture, you still must have the scheduler, and 
for simplicity in hardware, the database, on your low power server.  The 
scheduler is a very intensive bit of code.  With hundreds of channels 
across multiple sources with multiple tuners, it takes a whole lot of 
power to run.  It does not scale linearly, so as you start adding tuners 
and virtual tuners, it can get real messy real fast.  Once your 
scheduler runs start taking over a minute, it really starts being 
disruptive, and can cause delayed recordings.

Last, don't use a VM.  There is very little reason for any home user to 
need to use them.

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