[mythtv] Ticket #9773: Deadlocked BE

Daniel Kristjansson danielk at cuymedia.net
Mon May 16 01:46:58 UTC 2011

On Sun, 2011-05-15 at 22:57 +0200, Warpme wrote:
> On 5/15/11 8:30 PM, MythTV wrote:
> > #9773: Deadlocked BE
> > Comment (by danielk):
> >   It looks like in Thread #3 we are perhaps stuck waiting for a reply from
> >   the DB.
> On host with BE I have also running zoneminder (hause monitoring app).
> Zoneminder uses the same DB engine. During BE deadlock ZM was working OK 
> so I don't believe issue was because of hung/dead DB.
> If You can hint me for any checks I should do on deadlocked BE - pls 
> give me short guide. I'll be more than happy to do so !

No idea. I looked at the backtrace expecting to find that there was a
locking order problem caused by some lock in the EIT code + the
listening lock in mpegstreamdata. I expected to see the EIT code grab
a lock and then call an mpegstreamdata method that took the listening
lock + another thread that grabbed that same lock when processing an
mpegstreamdata callback where the listening lock was held. But if that
is happening, I missed it.

Instead what I noticed was threads waiting for the locks held by a piece
of code accessing the database. Perhaps it's just that piece of code
that is blocked, not whole full database. This could happen because of
table locking. My guess is that would depend on the database engine you
are using. Anyway, I'm not looking into this more right now. Perhaps
someone else will see "blocking on database" and have some ideas as to
what might be causing that.


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