Re: Admission Control

On 09/07/10 14:26, Robert Haas wrote:
> On Thu, Jul 8, 2010 at 10:21 PM, Mark Kirkwood
> <mark.kirkwood@catalyst.net.nz>  wrote:
>    
>> Purely out of interest, since the old repo is still there, I had a quick
>> look at measuring the overhead, using 8.4's pgbench to run two custom
>> scripts: one consisting of a single 'SELECT 1', the other having 100 'SELECT
>> 1' - the latter being probably the worst case scenario. Running 1,2,4,8
>> clients and 1000-10000 tramsactions gives an overhead in the 5-8% range [1]
>> (i.e transactions/s decrease by this amount with the scheduler turned on
>> [2]). While a lot better than 30% (!) it is certainly higher than we'd like.
>>      
> Isn't the point here to INCREASE throughput?
>
>    

LOL - yes it is! Josh wanted to know what the overhead was for the queue 
machinery itself, so I'm running a test to show that (i.e so I have a 
queue with the thresholds set higher than the test will load them).

In the situation where (say) 11 concurrent queries of a certain type 
make your system become unusable, but 10 are fine, then constraining it 
to have a max of 10 will tend to improve throughput. By how much is hard 
to say, for instance preventing the Linux OOM killer shutting postgres 
down would be infinite I guess :-)

Cheers

Mark