[mythtv] mythconverg on RAM drive?

Jack Perveiler perveilerj at yahoo.com
Fri Aug 4 20:46:51 UTC 2006

I can't claim to be an expert... I actually got the idea/technique of switching
to innodb from this archived mythtv-dev thread:


I then used the mysql docs for info on performance-tuning for innodb.


--- Steven Adeff <adeffs.mythtv at gmail.com> wrote:

> On 8/3/06, Jack Perveiler <perveilerj at yahoo.com> wrote:
> > >
> > > if you're having issues with MySQL taking too long, i suggest you first
> look
> > > at converting those tables from MyISAM to InnoDB.
> > >
> > > for many kinds of tables, InnoDB can be anywhere between 1.5x to 30x
> > > 'faster' -- _particularly_ when there are SQL 'DELETE' operations
> involved.
> >
> > InnoDB also has the advantage of having the actual db rows kept in memory
> by
> > mysql.  mysql only caches myisam indexes and lets the filesystem handle the
> row
> > caching, but with innodb you can tell mysql how much mem to allocate for
> the
> > rows (I think the parameter was something like "buffer_pool_size").
> >
> > I have a gig of ram, but when recording a number of high-bitrate programs
> the
> > filesystem cache filled up with recording data.  Going to disk to get the
> db
> > was causing me IOBOUND errors (this was back before Daniel vastly improved
> on
> > the IOBOUND errors in general), despite having all that ram.  Moving to
> innodb,
> > giving mysql something like a 300 meg buffer_pool, and turning my kernel
> > swappiness way down made a world of difference.  Everything from starting
> to
> > view a recording to scheduler re-schedules just became much snappier
> > (previously my disk would grind when starting either of those).
> >
> > I imagine this is one of those "your milage my vary" issues, but it
> certainly
> > helped my situation.  And having mysql handle the syncing to disk seems a
> lot
> > more safe than managing ramdisk-to-disk syncs on your own.
> >
> > --Jack
> I've found at times (like when in the Watch Recordings screen) where
> my wa% is quite high but my recordings drive is not anywhere near the
> read or write speeds I've seen the RAID array acheive before, though
> the system drive where my sql files are is high (though not that high
> from what I would figure).  I've also seen this happen randomly at
> other times, and MythWeb seems excruciatingly slow to bring up the
> Recorded Programs page. So perhaps its just MySQL processing things...
> Jack, how do I convert to InnoDB, etc?
> Thanks!
> (and sorry for having this on dev, but like I said in the OE, no one
> there had any thoughts)
> -- 
> Steve
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> http://www.mythtv.org/wiki/index.php/Frequently_Asked_Questions
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