[mythtv] mysql 5 bug affecting mythtv

Colin Guthrie mythtv at colin.guthr.ie
Thu Jan 31 21:31:17 UTC 2008


Daniel Kristjansson wrote:
> On Thu, 2008-01-31 at 14:39 +0000, Colin Guthrie wrote:
>> Dan Wilga wrote:
>>> At 2:09 PM -0800 1/30/08, Rob Smith wrote:
>>>> As for the mysql binary logs, that's done because mysql recommends and
>>>> defaults to having binlogs enabled. I personally think not having
>>>> binlogs is encouraging a foot shooting.
>>> IMHO, the only reason you would want to turn binary logs on is if you 
>>> are intending to use the replication or cluster features of MySQL. 
>>> Otherwise, all you're doing is eating up lots of disk space and a 
>>> non-trivial amount of CPU cycles.
>>>
>>> There is little benefit in keeping binlogs as a form of backup, 
>>> because on a busy system it would be very difficult to figure out 
>>> exactly where to start playing them back in order to recreate a 
>>> working system. They would have to be exactly synchronized with the 
>>> most recent file-based (mysqlhotcopy or equivalent) backup.
>> I find binlogs pretty useful in terms of a backup TBH.
>>
>> Every night I flush the logs, close all the db tables and take an LVM
>> snapshot of the database partition and back it up to a separate disk.
>> This is very quick to do, doesn't interrupt the service (much) and is
>> very quick to restore from too. Every hour I flush the binary logs and
>> copy them to a separate disk. That way even with a hideous server crash
>> the worst case scenario is 1 hour of data loss. The good thing with
>> snapshots is that it prevents the whole problem of backing up
>> non-transactional tables such as MyISAM.
>>
>> A replicated slave server would be better but if you can't justify the
>> expense of that, this is a pretty good system.
> 
> I disagree with the idea of having binlogs turned on by default, but
> the real problem was that they were not being rotated when Gentoo
> first introduced this default so they quickly filled up the var
> partition leading to data loss (the data loss on a full filesystem
> itself is arguably a mysql bug). I believe they are now rotated,
> but I'm not sure since I turn off binary logging immediately on my
> one remaining Gentoo box. The 'debug' problem happened because I began
> running Gentoo on my development box because I could easily make debug
> builds of everything, so I always have the debug use flag set, on the
> expectation that "-g" will be used whenever this doesn't mess up the
> build (some packages can't be compiled with debugging.) But whoever
> made the mysql ebuild decided to use the generic 'debug' flag to enable
> a  'mysql debug build' which creates a special build that is known to
> crash pretty much as soon as you connect to it on the Linux, OSX and
> AIX operating systems; instead they should have used a new flag like
> "mysqldebug" so if someone really wanted this very specialized build
> they could still enable it, but it wouldn't hurt everyone who just
> wanted the more useful core files that debug normally produces.
> 
> But even on other distros such as Ubuntu, Mandriva and Fedora I find
> that if the packaged version of an application doesn't work, compiling
> that application from source usually fixes the problem. So I don't mean
> to single Gentoo out, except to note that I've had two problems with
> the mysql build in the past. I don't particularly like the mythtv
> packages used by any of the distro's. Ubuntu's is probably my favorite
> since they moved to using the profile target + stripping, but it doesn't
> turn on rtc for better playback when OpenGL V-Sync isn't available.
> The Gentoo ebuild's biggest sin is that there are some dangerous USE
> flags and the only warning you get scrolls by quickly as you build all
> your packages. This is not a general problem with the warnings issued by
> the Gentoo packages, they are buried in trivial status output from the
> compile process itself unless you install each packages manually and
> don't use the nifty dependency resolving features of the ports system.
> 
> We're getting way off topic here, so I'll stop responding unless this
> thread is moved over to the user's mailing list. Just to summarize, I
> highly recommend rebuilding mysql & mythtv by reading the build guides
> and using "./configure --help" and without ebuild assistance.

If there is anything you'd recommend packaging wise, I'm all ears as
I've not long ago taken over the Mandriva package. :)

Col

-- 

+------------------------+
|     Colin Guthrie      |
+------------------------+
| myth(at)colin.guthr.ie |
| http://colin.guthr.ie/ |
+------------------------+


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