[mythtv-users] Lengthy delay watching recordings

[Terjesen Jens Peder]

-----Original Message-----
On 22. mai 2012 9:46 Michael T. Dean wrote:

On 05/22/2012 02:19 PM, Rich West wrote:
> I noticed that going to 0.25 about a month back that the delay to 
> start playing an HD video had increased substantially and was curious 
> as to what might be the cause.
>
> As I looked further, I realized that it is with all video, but HD 
> content appears to be the most obvious offender.  It can take up to 31 
> seconds from the moment the user selects the video to play before it 
> actually starts playing.
>
> My backend system is well used, but from the graphs I have, it's not 
> hurting with CPU or memory.  Network to the frontends are all 
> hardwired (backend is gig, frontends are 100 meg).  From a utilization 
> perspective, the drives on the backend server are always hovering at 
> around 85% utilization, which is good, and the general I/O on the 
> drives is not such that it would cause a negative impact.
>
> I am using commercial detection, so I do suspect that there is some 
> form of buffering going on, but for 31 seconds?  No network errors on the
> switch or the interface for the frontend or the backend.    CPU
> utilization on the frontend is low.. basically idle.
>
> I'm just wondering if there is a particular place within MythTV to 
> look (for example, I recently found that it was recommended that 
> "quick tuning" should be enabled for the hdhomerun)..
>

/me guesses you have MySQL data on a file system with barriers enabled.

Mike
-----Original Message-----

I don't have this problem but get irregular periods of freezes on the frontend.
I am not so sure that barriers enabled or not is the cause of this, based on the following observations.

On my combined FE/BE I was running 0.24 until the beginning of December 2011 without any problems like this.
I then switched to the development 0.25-pre version because of frequent tuning problems, and updated regularly until 0.25 was released.

Up until some time early in 2012, probably around February/March there were still no problems with freezing.
After this point in time I started to get 30-120 second freezes on the frontend. After some time I found that the mysqld process was using near 100% of one core for very long periods, and the freezes coincided with this.

After getting an UPS working for the FE/BE I disabled barriers on the OS/database partition which is EXT4.
The rescheduling time went down from about 25-30 seconds to about 15 seconds, but the freezes where still the same.

Using SHOW PROCESSLIST; in mysql showed that insertions and modifications of the program table had a status of LOCKED for long periods of time while the mysqld CPU load was at near 100%.
http://www.gossamer-threads.com/lists/mythtv/users/510064#510064

Being a little desperate I deleted all recording rules, and the freezes and high CPU load where all gone.
Well a PVR without any recording rules isn't of much value, so after monitoring for a while I started adding recording rules back. With just a few recording rules the system worked fine. Now when I am more or less back at the same number of recording rules I see freezes lasting from 10-25 seconds.

Jens