[mythtv-users] 0.27: Stalls and other niggles
Michael T. Dean
mtdean at thirdcontact.com
Thu Jan 16 18:27:00 UTC 2014
On 01/16/2014 11:32 AM, Mike Thomas wrote:
> What I have noticed is mysqld almost always seems to be the process
> doing the most I/O at the moment of the stall, but is rarely doing any
> I/O at other times. It is almost as if mysqld is batching updates to
> its tables and logs.
Sounds like you're storing your MySQL data on a file system with
barriers enabled, so mysqld writes data to disk and the file system
barriers cause it to block until all data is physically written to disk
platters (not just to disk cache)--which takes a long time. During this
time, MythTV (and everything else) is unable to access required data in
MySQL.
The proper fix is /not/ just disabling barriers, instead making it so
that data can be written safely--using barriers--fast enough to prevent
impacts to system services. There are many things you can do to fix
this, each with its own advantages/disadvantages (and costs), but before
going there, I'd recommend just remounting your MySQL-data-containing
file system with barriers disabled to see if this is, in fact, the
problem you need to fix. If so, then come back to find the best fix for
you.
Mike
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