Re: Benchmarking a large server

On Mon, 9 May 2011, David Boreham wrote:

> On 5/9/2011 6:32 PM, Craig James wrote:
>> Maybe this is a dumb question, but why do you care?  If you have 1TB RAM 
>> and just a little more actual disk space, it seems like your database will 
>> always be cached in memory anyway.  If you "eliminate the cach effect," 
>> won't the benchmark actually give you the wrong real-life results?
>
> The time it takes to populate the cache from a cold start might be important.

you may also have other processes that will be contending with the disk 
buffers for memory (for that matter, postgres may use a significant amount 
of that memory as it's producing it's results)

David Lang

> Also, if it were me, I'd be wanting to check for weird performance behavior 
> at this memory scale.
> I've seen cases in the past where the VM subsystem went bananas because the 
> designers
> and testers of its algorithms never considered the physical memory size we 
> deployed.
>
> How many times was the kernel tested with this much memory, for example ? 
> (never??)
>
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