Negative caching

Karl F. Larsen klarsen1 at
Fri Jun 19 06:20:00 UTC 2009

Hash: SHA1

Hal Burgiss wrote:
> On Fri, Jun 19, 2009 at 03:24:19AM -0700, Steve Lamb wrote:
>> Hal Burgiss wrote:
>>> I think I've figured out why recent Ubuntu has such abysmal performance. Very
>>> cleverly over a period of time, it takes all the free memory and uses it to
>>> store useless junk that you will never ever use. And then holds on to the
>>> useless stuff as long as it possibly can. And then you are forced to
>>> work out of swap.
>>      Uhm... no.  Simple as that.  Whatever your problem is has no relation to 
>> caching or buffers.  At least if it is you certainly have quite a further 
>> distance to go to prove it than what you've presented in your message.  The 
>> cached pages, for all intents an purposes, can be considered free.  The 
>> difference between a cached page and a free page is just a couple of bits in a 
>> memory map.
> Actually I was trying to blend a little humor with a bad situation that I
> don't fully understand. I have been a Linux only user since Redhat4 (late
> 90's). The last version of windows I owned personally was 3.1. The current
> Ubuntu (desktop) is the poorest performing Linux systems I have experienced in
> that time. On Redhat, I have had desktop X sessions that lasted over a year.
> That is unthinkable now. I am living in terms of weeks, before the system is
> either so slow or slow flaky, a reboot is the best remedy. I have both home
> and work systems on 9.04. And both are problematic. Both ran fine on 8.04. I
> have a number of 8.04 servers that are also fine (but I never run X on
> servers). 
> [hal at admin1 clients]$ uptime
>  07:58:31 up 353 days, 21:25,  2 users,  load average: 0.00, 0.00, 0.00
> That's a 8.04 LAMP server that seems to run flawlessly.
>>      Your speed settings have to the result of something else going on because 
>> the caching that the kernel does, if it were the cause, would be evident to 
>> more people with heavier usage patterns than you.  It is the most commonly 
>> maligned function the kernel performs.  ;)
> I am totally open to other causes/solutions. But what is a better explanation
> of a previously happy system whose performance degrades consistently and
> severely over time? And when left idle for long periods of time, goes
> completely in the toilet, to the point of it taking seconds for windows to
> show any response whatsover to mouse clicks, seconds for keystrokes to appear
> in text terminals, and minutes for new windows to open? A reboot or a restart
> of X will bring back "normal" responsiveness immediately, only to degrade
> again in days/weeks. There is no sign of excessive CPU usage, and no single
> program is taking excessive memory (at least as reported). It seems to have
> all the earmarks of a really wacky swap problem. If not, its doing a good
> imitation of one. 
> I am also a victim of the intel chipset trainwreck, so that may be a
> complicating factor (on my home system), but doesn't explain a slow,
> consistent degration that eventually makes the system unusuable. The work
> desktop does not degrade as badly and I use compiz effects on that one, so
> that might be another complicating factor there. 
> Thanks! 
	Slow can be a shortage of RAM. And I think you have lots but it might
not all may be working. Use a Terminal with top to measure your RAM and
swap usage. Let us know what it shows when you you slow down.

73 Karl

- --

	Karl F. Larsen, AKA K5DI
	Linux User
        Key ID = 3951B48D

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