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

[Jim Kinney]

If swap fills to 100%, cache is dropped to make room for more app use of
RAM.  Once that last non-active ram is used up, the system will begin
delivering oom errors. If the oom occurs on an application, the application
will either halt or crash (depends on code - halt is recommended). If the
oom occurs on a kernel process, the system will crash (usually).
A process halted by an oom error is still in memory and will ned to be
closed out to free ram.

It's pretty easy to add more swap space. Anthing over 2G is pretty useless
though. The kernel is good abouttracking swap use so it won't try and write
1.1G to a 1G swap.

On Fri, Jun 27, 2008 at 6:01 PM, Jerry Yu <jjj863 at gmail.com> wrote:

> On a db server with 16G ram and 1G swap, swap is nearly full. (It
> swang between 88 and 96% last week). What's the worst-case scenarios
> in terms of performance and/or availabilitu, when kernel decides to
> page out a few extra idle pages (more than the free space in swap)
> from physical ram?
>
> Assume the following,
> * Free physical ram is at 5G, or 9G including buffer/cache.
> * no new program will be launched, except stock RHEL 5.1 cron jobs and
> a few ssh sessions
> * OLTP transaction load against the db may spike 5 times over the
> weekly average, with more client connections to db server
> * swappiness is at default
> * db is the only non-os process running. Mem for db is preallocated.
> No tweaks is done to prevent db pages from being paged out
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-- 
-- 
James P. Kinney III
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