[mythtv-users] Sudden seemingly-random database issues

[Brian S]

Apologies if this comes through twice - mail reader bonked out while 
sending previously and it doesn't appear to have sent. At this point, 
waiting to see what other computing device I can goof up this week, heh.

> On Mon, Sep 22, 2014 at 8:01 PM, Brian S <inanimatecrbnrod at hotmail.com 
> <mailto:inanimatecrbnrod at hotmail.com>> wrote:
>
>  --- Wall of text deleted ---
>
> I think one of the fixes posted here will probably help:
>
> http://askubuntu.com/questions/127264/cant-start-mysql-mysql-respawning-too-fast-stopped
>
> Tom
>

Thanks for the response, and my apologies on the wall-of-text...using a 
mail reader now which should play nicer.

Using the information in the link above, I'm making a little progress, 
but I'm having trouble figuring out exactly what is causing the issue 
and therefore which fix on the link could solve the problem. Given I'm 
green with this sort of thing, I'm hesitant to start changing things 
like apparmor or reinstalling mysql unless I'm reasonably certain that's 
the cause, if that makes sense.

Below is the terminal output from 'sudo mysqld --verbose' which I assume 
is trying to help me narrow down what the issue is. The output suggests 
there is a possibility of DB corruption, which given how the issue of 
the database just kinda vanishing while the BE was running and then not 
being able to connect upon reboot might make sense, but is there some 
way to verify the DB actually is corrupt before attempting to 
fix/restore? (And I don't think I can run the backup/restore scripts 
anyway unless I can get mysql up and running anyway maybe?)
I searched for the error in the output below, and there is some 
suggestion of changing a flag in my.cnf to " innodb_force_recovery = 4" 
to get it to go again, which maybe then I could at least to a 
backup/restore? My concern here would be could I possibly trash 
something even worse, or am I already far enough up a creek that there's 
nothing to really worry about?
So I guess longish post made short, based on below, what should I be 
looking for next? There's a link below that explains how to recover a DB 
- I can try that, but again I'm not sure if that's what I should try.


140924 19:08:47 [Note] Plugin 'FEDERATED' is disabled.
140924 19:08:47 InnoDB: The InnoDB memory heap is disabled
140924 19:08:47 InnoDB: Mutexes and rw_locks use GCC atomic builtins
140924 19:08:47 InnoDB: Compressed tables use zlib 1.2.3.4
140924 19:08:47 InnoDB: Initializing buffer pool, size = 128.0M
140924 19:08:47 InnoDB: Completed initialization of buffer pool
140924 19:08:47 InnoDB: highest supported file format is Barracuda.
140924 19:08:47  InnoDB: Waiting for the background threads to start
140924 19:08:48 InnoDB: 1.1.8 started; log sequence number 148327708
140924 19:08:48 [Note] Server hostname (bind-address): '0.0.0.0'; port: 
3306
140924 19:08:48 [Note]   - '0.0.0.0' resolves to '0.0.0.0';
140924 19:08:48 [Note] Server socket created on IP: '0.0.0.0'.
140924 19:08:48  InnoDB: Assertion failure in thread 140657319352064 in 
file trx0purge.c line 829
InnoDB: Failing assertion: purge_sys->purge_trx_no <= 
purge_sys->rseg->last_trx_no
InnoDB: We intentionally generate a memory trap.
InnoDB: Submit a detailed bug report tohttp://bugs.mysql.com 
<http://bugs.mysql.com/>.
InnoDB: If you get repeated assertion failures or crashes, even
InnoDB: immediately after the mysqld startup, there may be
InnoDB: corruption in the InnoDB tablespace. Please refer to
InnoDB:http://dev.mysql.com/doc/refman/5.5/en/forcing-innodb-recovery.html
InnoDB: about forcing recovery.
00:08:48 UTC - mysqld got signal 6 ;
This could be because you hit a bug. It is also possible that this binary
or one of the libraries it was linked against is corrupt, improperly built,
or misconfigured. This error can also be caused by malfunctioning hardware.
We will try our best to scrape up some info that will hopefully help
diagnose the problem, but since we have already crashed,
something is definitely wrong and this may fail.

key_buffer_size=16777216
read_buffer_size=131072
max_used_connections=0
max_threads=151
thread_count=0
connection_count=0
It is possible that mysqld could use up to
key_buffer_size + (read_buffer_size + sort_buffer_size)*max_threads = 
346679 K  bytes of memory
Hope that's ok; if not, decrease some variables in the equation.

Thread pointer: 0x0
Attempting backtrace. You can use the following information to find out
where mysqld died. If you see no messages after this, something went
terribly wrong...
stack_bottom = 0 thread_stack 0x30000
mysqld(my_print_stacktrace+0x29)[0x7fed6c8ab459]
mysqld(handle_fatal_signal+0x483)[0x7fed6c7711d3]
/lib/x86_64-linux-gnu/libpthread.so.0(+0xfcb0)[0x7fed6b4c5cb0]
/lib/x86_64-linux-gnu/libc.so.6(gsignal+0x35)[0x7fed6ab35445]
/lib/x86_64-linux-gnu/libc.so.6(abort+0x17b)[0x7fed6ab38bab]
mysqld(+0x5e1b14)[0x7fed6c93eb14]
mysqld(+0x5e1f31)[0x7fed6c93ef31]
mysqld(+0x6a6d8f)[0x7fed6ca03d8f]
mysqld(+0x69d955)[0x7fed6c9fa955]
mysqld(+0x5e3dfe)[0x7fed6c940dfe]
mysqld(+0x5d4d9c)[0x7fed6c931d9c]
mysqld(+0x5d91a3)[0x7fed6c9361a3]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x7e9a)[0x7fed6b4bde9a]
/lib/x86_64-linux-gnu/libc.so.6(clone+0x6d)[0x7fed6abf14bd]
The manual page athttp://dev.mysql.com/doc/mysql/en/crashing.htmlcontains
information that should help you find out what is causing the crash.