[ale] Kernel 2.6 : worst-case scenarios if swap full

[Jeff Lightner]

Maybe but does Linux not do virtual memory pool of both swap and
physical memory?   On UNIX such as HP-UX there is value in having larger
swap simply because it allows a larger preallocation of virtual memory
by processes thereby allowing more to be started at the same time.
This preallocation is for memory that is never really used for the most
part.

 

The key in the OP though was DB and that is a little different.  It
doesn't say what DB.  I haven't done anything with MySQL but Oracle uses
its own SGA which is in Shared Memory for the most part.   Swap really
isn't the issue for DB.  Your DB ought to be using space that isn't
using buffer cache either because it and the SGA's own caching mechanism
interfere with each other.   Since I've only done Oracle on OCFS (Oracle
Cluster Filesystem) or ASM raw devices I haven't investigated disabling
buffer cache for ext3 or other filesystems.  It is something we
routinely do for our Veritas filesystems on HP-UX.

 

________________________________

From: ale-bounces at ale.org [mailto:ale-bounces at ale.org] On Behalf Of Jim
Kinney
Sent: Saturday, June 28, 2008 1:09 PM
To: ale at ale.org
Subject: Re: [ale] Kernel 2.6 : worst-case scenarios if swap full

 

 

On Sat, Jun 28, 2008 at 10:42 AM, Ed L. Cashin <ecashin at noserose.net>
wrote:

2008/6/28 Jim Kinney <jim.kinney at gmail.com>:
...

> It's pretty easy to add more swap space. Anthing over 2G is pretty
useless
> though.

I think there was a time when the kernel could not use more
than 2 GB from a swap partition, but unless there has been
a regression, I would expect today's kernels to use large swap
areas without trouble.


It is not a problem for the kernel to TB's of swap. It simply becomes
useless due to access speeds after about 2GB. 

	
	
	If there's a limit, though, I'd like to know about it.  So any
	references where I could read about it would be appreciated.
	
	--
	 Ed Cashin <ecashin at noserose.net>

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-- 
-- 
James P. Kinney III
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