[mythtv-users] Backend crashes after using Mythweb

James Guard james at quiver.net
Mon Dec 5 13:01:32 EST 2005


Backend crashes after using Mythweb have been mentioned on the list before. 
No one seemed to know what was causing it and there didn't seem to be a
resolution to the problem (or maybe I didn't search for long enough...).

While I don't have a resolution I do seem to have stumbled across the
cause (or at least where the cause might be found).

I have half a dozen or so programs that I record, with between 1 and 190 or
so episodes for each title.

Doing a "Show recordings" in Mythweb for each program title group causes no
problems except for one program title group and the "All recordings" group. 
As soon as I view this program title group or "All recordings", mythbackend
starts starts using all the CPU, but still "works" (ie. I can do other
things via Mythweb - eg. look at recording schedules, or listings).
mythbackend continues to use all spare CPU until it is restarted

If I delete a recording from one of the "safe" program title groups there is
no problem with mythbackend.

If I delete a recording from the "unsafe" program title group (after
restarting mythbackend), mythbackend uses all the CPU and no longer responds
to other requests.
A strace at this point shows:

Process 5566 attached - interrupt to quit
futex(0x82f4ee4, FUTEX_WAIT, 2, NUL

I have to restart mythbackend at this point.

This problem is relatively recent (within the last month or so).  I have
been running a myth system since June and I have made no recent changes to
either the frontend or backend before this problem occurred.

It seems to me that there might something in the database related to this
program title group that is causing the problem when using the web frontend.

I was going to send the email at this point, but I looked a bit further...

I've had a look at the "recordedprogram" section of a database dump and
there are no control characters in the data.

I put some debugging and sleeps in recorded_programs.php and narrowed it
down to a single recording that was causing this.  After deleting the
recording the problem no longer occurs.

I cannot see anything wrong with the entry as dumped from the database
before I deleted it.

The only thing that sticks in my mind about the nuv file is that it was
exactly 1024MByte in size (as reported by Mythweb).

Hopefully this might help someone else with a similar problem in the future.



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