MySQL slow queries, small tables

Corey Edwards tensai at zmonkey.org
Tue Jun 10 15:10:05 MDT 2008


On Tue, 2008-06-10 at 14:45 -0600, Dave Smith wrote:
> I just noticed that vim also suffers like MySQL. If I open a new file in 
> vim, add a line of text and run :w, it can take 1 minute to save while 
> 'cat /dev/zero > /tmp/foo.bin' is running. I think it's probably related 
> to this ext3 fsync bug (thanks Byron for pointing that out to me):
> 
>     http://shaver.off.net/diary/2008/05/25/fsyncers-and-curveballs/

That does sound likely.

> I am now thinking I need to put my MySQL data on a separate partition of 
> its own (so it doesn't have to share a file system with evil doers like 
> cat).

I'm not certain that will have an effect, for two reasons. Last I knew
(which was a few years ago, so this may have changed), the kernel disk
elevator was ignorant of partitions and treated each disk as a whole.
That means that writes to one partition can interfere with writes to
another.

Second, from that post it sounds like fsync is flushing all of the
kernel disk buffers regardless of which partition they're headed to. I
could be mistaken her though. I guess if you put MySQL on a non-ext3
partition that might do the trick. Maybe try a RAM disk. I bet it would
be a lot faster. :)

Corey

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