[Gllug] Swap Restrictions

[Ian Northeast]

Christian Smith wrote:
> On Wed, 12 Apr 2006, Steve Nelson wrote:
> 
> 
>>Hello All,
>>
>>
>>Finally, I have just built another two machines, both with 8G of RAM.
>>The client requested 16G of swap(!).  There weren't enough partitions
>>to make 8 x 2G partitions, and surely this is overkill anyway, even
>>for a very very busy Oracle server?  I created 3 x 2G.  Just wondered
>>what we think about such large swap partitions, and how they should be
>>created?  More extended partitions and multiples of 2G?
> 
> 
> 
> 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 about two decades out of date.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.
> 
> If an Oracle server is having memory paged out to swap and discarded, then
> that is defeating the Oracle caching.

I have seen one case where this sort of thing was justified. It is a 
test server with about 5 web servers, 3 instances of tomcat, an Oracle 
iAS and a few miscallaneous bits and pieces crammed in. Its production 
equivalent has 7 separate servers. This lot has an enormous memory 
footprint just sitting there doing nothing, which is what it does most 
of the time. So when it had 1GB of swap space and 2.5GB of RAM it kept 
failing because it filled swap. So it ended up with 8GB of swap and 
stabilised.

This is OK for this particular machine as performance isn't critical and 
it isn't even used very much. There isn't much swapping activity, just 
utilisation. On a production machine I would indeed have added RAM.

This has just 2 swap partitions, the original 1G one and a 7G one. It 
seems to work OK but as I said swap activity isn't high.

Regards, Ian

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