[mythtv-users] Tracing Instability

Ken Smith kens at kensnet.org
Sun Aug 14 21:40:15 UTC 2011

Brian J. Murrell wrote:
> On 08/13/2011 05:32 PM, Ken Smith wrote:
>> Hi, I'm on the trail of some instability (random hanging) of my
>> Mythbackend.
> Welcome to the club.
>> I've set up a script based on
>> http://tweakingmythtv.wordpress.com/2011/01/11/mythbackend-deadlocks-and-auto-restart-script/
>> to catch the problem and restart the backend.
> Interesting.  The only problem with that script is that it might restart
> the backend while it's recording something (mine seems to only lock up
> when recordings are in progress) and no clients are needing to connect,
> needlessly interrupting a recording.
Yes it does that. I had an hour long recording in 6 parts the other 
day... A few days ago I ran a backup app that loaded the machine very 
heavily and the Mythbackend was restarted, by my heartbeat script, on 
average every 4 mins over a period of 4 hours. Fortunately nothing was 
scheduled to record at the time. In the end I stopped myth and let the 
backup complete. It was seeing that happen that pointed me toward the 
theory that the mythbackend hangs might be related to CPU load. It's on 
14,000 bogomips at the moment.
>> mythtv-backend-0.24.1-275  (atrpm's build)
>> mysql-5.0.77-4.el5_6.6
>> 2.6.18-238.12.1.el5.centos.plus 64 bit
> So, now we have one on Ubuntu (me) one on Gentoo (IIRC) (warpme) and one
> on CentOS.  It is an interesting data point that it's not isolated to a
> single distribution.
>> Any suggestions as to what I should look at to narrow this down.
> Well, you can start by searching the very recent archives for a long
> thread about this issue.
Yes, re-read those and the bug reports today.

As a datapoint, I am using the OTA program guide and I don't run 
commflagging. I also have a few applications that make occasional use of 
other databases in mysql.

As another datapoint, mysql's files are on a raid5 ext3 file system 
hosted on a 3ware controller with IDE physical disks. The video files 
are on a single non raid sata disk. The performance of the 3ware isn't 
that spectacular and I see average 8% iowait according to sar. Also, I 
have noticed that the machine has used the swap file in the last few 
days so I have another Gig of ram on its way.

Currently I've set my mythbackend and mysql to run at nice -3 to give 
those processes priority over the slew of other things that server does. 
No restarts since I did that about 12 hours ago.

How different is the 0.23 schema from 0.24? All I would need to save is 
my recorded programs. The rest can be recreated. Is a downgrade at all 
possible until maybe this problem is fixed in 0.25?

For now I'll see if my nice -3 setting and another gig of ram helps 
before I do anything more drastic.

Thanks.... Ken

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