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From Erick Erickson <erickerick...@gmail.com>
Subject Re: Strange performance behaviour when concurrent requests are done
Date Fri, 29 Apr 2011 12:29:58 GMT
I'd guess that what's happening is that you're pegging the CPU with 4
threads, serving up the absolute maximum that the machine will
handle. The thing to look at is the throughput rather than avg
response time (although that's going down but not as rapidly, which
is still a bit puzzling).

Usually, adding more threads can increase throughput by allowing
threads to steal some cycles while other threads block on,
say, I/O. But if the CPU utilization is 100% adding more threads will
not increase throughput, they just wait for each other.

So your average response time includes the time threads are waiting, the
context switching that Grijesh spoke of.

So look at your machine with a performance monitor and see if your
CPU is pegged. Or, more accurately, whether your CPU is pegged
when 4 threads are active.

Best
Erick

On Fri, Apr 29, 2011 at 7:43 AM, Marc Sturlese <marc.sturlese@gmail.com> wrote:
> That's true. But the degradation is so big. If you use lunch concurrent
> requests to a web app taht doesn't use Solr the time per request won't
> degradate that much. For me, it looks more like a synchronized is happening
> somewhere in Solr or Lucene and is causing this.--
> View this message in context: http://lucene.472066.n3.nabble.com/Strange-performance-behaviour-when-concurrent-requests-are-done-tp505478p2878856.html
> Sent from the Solr - User mailing list archive at Nabble.com.
>

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