[Gllug] Swap Restrictions

[Alain Williams]

On Tue, Apr 18, 2006 at 03:16:16PM +0100, Christian Smith wrote:

> Ask why they want 16G of swap. If it's the old 2x RAM rule, then they are
> about two decades out of date.
> 
> If they are epecting to use more than 8G of RAM, then I'd recommend they
> spend the money on that extra RAM instead of admin time on swap.

Yep. The only sorts of things that should end up on swap are the shell scripts
that invoked long running applications & the login shells on the unused virtual terminals.

> If an Oracle server is having memory paged out to swap and discarded, then
> that is defeating the Oracle caching.
> 
> The swap file is used in Linux (and Solaris, and HP-UX, and AIX ...) for
> anonymous data only. As such, only anonymous data like heaps, stacks and
> shared memory segments will compete for swap, and if you have an anonymous
> memory usage of anywhere near 2x RAM, then your machine is too overloaded.
> 
> Linux will write memory to swap speculatively in order to be able to
> discard anonymous memory with no delay should it need to. If the server is
> properly sized, then a nominal amount of swap should be sufficient. Just
> give the servers a single 2G swap partition.

-- 
Alain Williams
Parliament Hill Computers Ltd.
Linux Consultant - Mail systems, Web sites, Networking, Programmer, IT Lecturer.
+44 (0) 787 668 0256  http://www.phcomp.co.uk/

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