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Old 04-22-2010, 04:52 PM
Alan McKinnon
 
Default gentoo-box stopping services

On Thursday 22 April 2010 18:24:08 Stefan G. Weichinger wrote:
> Am 22.04.2010 17:50, schrieb Alan McKinnon:
> >> Shouldn't the kernel *swap* then ?
> >
> > No, the OOM killer kicks in when the kernel has no more virtual memory,
> > including swap. Either way, more RAM is the answer. Or fidn the app with
> > the memory leak if you are unlucky enough to have one of those running
> > around.
>
> The added swapfile with one GB won't help here for a start?

It will certainly help. If your core problem is simply not enough RAM, then 1G
more might be all you need. You'd have to run checks and do some monitoring to
see if performance is affected.

I haven't followed the full thread so I don't know what you are running; and
some daemons perform really badly if they have to touch swap. Apache for
example, a busy MTA for another - disks are thousands of times slower than
RAM, so if a webserver has to swap memory back in from disk, it almost
instantly brings the server to a grinding halt.

On my web and mail servers I have no swap at all, they do have lots and lots
of RAM; my Sybase database servers have enormous amounts of swap. Each server
has been profiled so it is set up to be as close to ideal as I can determine.

--
alan dot mckinnon at gmail dot com
 
Old 04-22-2010, 09:16 PM
walt
 
Default gentoo-box stopping services

On 04/22/2010 09:52 AM, Alan McKinnon wrote:


On my web and mail servers I have no swap at all, they do have lots and lots
of RAM; my Sybase database servers have enormous amounts of swap...


Hm. Does that mean your database servers are allowed to be slower than the web
and mail servers?
 
Old 04-22-2010, 09:46 PM
Alan McKinnon
 
Default gentoo-box stopping services

On Thursday 22 April 2010 23:16:56 walt wrote:
> On 04/22/2010 09:52 AM, Alan McKinnon wrote:
> > On my web and mail servers I have no swap at all, they do have lots and
> > lots of RAM; my Sybase database servers have enormous amounts of swap...
>
> Hm. Does that mean your database servers are allowed to be slower than the
> web and mail servers?

No, it means that the database software intelligently handles swap.

An enterprise grade db like this one will load many megabytes of data in huge
chunks on and off disk in one action. If you are dealing with tables
containing many millions of rows, you really do want this behaviour. Without
swap, the db will still load and unload many megs of data at a time on and off
disk, so there is no appreciable downgrade of performance, but I do have the
benefit of keeping data in virtual memory for longer using swap. The database
code pages are never swapped by design - doing that is just plan stupid.

The web and mail servers on the other hand deal with millions of small files,
on the order of 10k each. Allowing that to swap is catastrophic.


--
alan dot mckinnon at gmail dot com
 
Old 04-23-2010, 03:28 AM
Stroller
 
Default gentoo-box stopping services

On 22 Apr 2010, at 17:24, Stefan G. Weichinger wrote:


Am 22.04.2010 17:50, schrieb Alan McKinnon:


Shouldn't the kernel *swap* then ?


No, the OOM killer kicks in when the kernel has no more virtual
memory,
including swap. Either way, more RAM is the answer. Or fidn the app
with the
memory leak if you are unlucky enough to have one of those running
around.


The added swapfile with one GB won't help here for a start?


Yes, it will. If it's running out of RAM+swap, then more swap will help.

Stroller.
 
Old 04-23-2010, 08:17 AM
"Stefan G. Weichinger"
 
Default gentoo-box stopping services

Am 23.04.2010 05:28, schrieb Stroller:

>> The added swapfile with one GB won't help here for a start?
>
> Yes, it will. If it's running out of RAM+swap, then more swap will
> help.

I watch the system now, only 6 MB of RAM free now ... the AV-scanners
grab the most ... I already deactivated f-secure (fsavd) because it
timed out while scanning a 10k text-mail :-(

Gotta get some RAM, yes.

S
 

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