Re: [gentoo-user] mysqld invoked oom-killer

[Alan McKinnon]

On Thursday 21 July 2011 17:26:33 kashani did opine thusly:
> On 7/21/2011 4:53 PM, Grant wrote:
> > So swap isn't treated exactly like RAM.  It actually has special
> > handling in Linux which makes it beneficial to have on almost
> > any
> > Linux system?  According to Alan, things get very bad when a
> > Linux system hits swap.  How can behavior like this be
> > beneficial:
> >
> > "When a linux machine hits swap, it does so very aggressively,
> > there is nothing nice about it at all. The entire machine slows
> > to a painstaking crawl for easily a minute at a time while the
> > kernel writes pages out to disk, and disk is thousands of times
> > slower than RAM.
> >
> > It gets so bad that you can't even run a shell properly to try
> > and see what's going on and kill the actual memory hog."
> >
> > Also, aren't you likely to wear out your hard disk sooner using
> > swap?
>
> 1. swap is good. Unless you have a good reason, leave it there. You
> do not have a good reason to remove it and neither does anyone
> else.
>
> 2. Don't use the swap that you have. It's slow. It is not a
> replacement for RAM.
>
> 3. If you use a little bit of swap, 100-200MB, that's fine. It's
> also a sign you need more RAM.
>
> 4. If you're using all your RAM and a couple of GB of swap, you're
> screwed. Avoid this.
>
> 5. Swap that you never write to or read from never needs to hit the
> drives. If you're worried about drive wear, turn off logging.

Excellent summary of swap; says a lot of what I was trying to say but 
didn't succeed.

I might argue with your point #1, but then I would be nit-picking and 
it's very dependant on circumstance anyway. As in all things IT, YMMV

-- 
alan dot mckinnon at gmail dot com