Thread: size of cache

size of cache

From
Jean-Max Reymond
Date:
with my application, it seems that size of cache has great effect:
from 512 Kb of L2 cache to 1Mb boost performance with a factor 3 and
20% again from 1Mb L2 cache to 2Mb L2 cache.
I don't understand why a 512Kb cache L2 is too small to fit the data's
does it exist a tool to trace processor activity and confirm that
processor is waiting for memory ?
does it exist a tool to snapshot postgres activity and understand
where we spend time and potentialy avoid the bottleneck ?

thanks for your tips.

--
Jean-Max Reymond
CKR Solutions Open Source
Nice France
http://www.ckr-solutions.com

Re: size of cache

From
Simon Riggs
Date:
On Wed, 2005-07-13 at 10:20 +0200, Jean-Max Reymond wrote:
> with my application, it seems that size of cache has great effect:
> from 512 Kb of L2 cache to 1Mb boost performance with a factor 3 and
> 20% again from 1Mb L2 cache to 2Mb L2 cache.

Memory request time is the main bottleneck in well tuned database
systems, so your results could be reasonable.

> I don't understand why a 512Kb cache L2 is too small to fit the data's
> does it exist a tool to trace processor activity and confirm that
> processor is waiting for memory ?

You have both data and instruction cache on the CPU. It is likely it is
the instruction cache that is too small to fit all of the code required
for your application's workload mix.

Use Intel VTune or similar to show the results you seek.

Best Regards, Simon Riggs