[mythtv-users] Backend hanging

[Mark Smith]

Ever since upgrading to MythTV 0.22 I've been suffering from an issue
where the backend hangs, seemingly on a random basis. This often
results in failed recordings, usually with the backend having set up
an entry in the recordings table, but not actually recorded anything
(the Recorded Programs view in Mythweb shows the length as 'B').

Further investigation suggests that it's related to database
transactions failing to start and probably blocking threads in the
backend as a result:

mysql> show innodb status;

------------
TRANSACTIONS
------------
Trx id counter 0 21840
Purge done for trx's n:o < 0 7024 undo n:o < 0 0
History list length 6
LIST OF TRANSACTIONS FOR EACH SESSION:
---TRANSACTION 0 21839, not started, process no 8077, OS thread id
140659755308816
MySQL thread id 141, query id 6347259 localhost mythtv
---TRANSACTION 0 0, not started, process no 8077, OS thread id 140659867965200
MySQL thread id 140, query id 6347263 localhost root
show innodb status
---TRANSACTION 0 21838, not started, process no 8077, OS thread id
140659844314896
MySQL thread id 138, query id 6347117 localhost mythtv
---TRANSACTION 0 21837, not started, process no 8077, OS thread id
140659868763920
MySQL thread id 134, query id 6346878 localhost mythtv

Restarting mysqld when the backend is in this state seems to clear the
blockage, resulting in a series of errors in the log complaining that
the database has gone away (as you might expect) - mostly relating to
a backlog of EIT updates.

The log is otherwise not showing anything of relevance, though I'll
have a look at setting more verbose database logging for next time it
occurs.

Questions:

Has anyone experienced any problems similar to this?

Is there any way of finding out more information about these database
transactions in mysql in the hope of understanding why they are stuck
in this state?

Any other suggestions?

--
Mark Smith - Hampshire, UK
http://www.chez-moi.org.uk/