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From Michael Greene <michael.gre...@gmail.com>
Subject Re: Cassandra performance
Date Tue, 18 Aug 2009 19:02:00 GMT
According to the HBase guys and confirmed by
http://java.sun.com/javase/technologies/hotspot/gc/gc_tuning_6.html#icms,
on an 8-core machine you are not going to want to enable
-XX:+CMSIncrementalMode -- it is for 1 or 2 core machines that are
using the CMS GC.  This should affect your latency numbers positively,
but I wouldn't see it changing the CPU usage much.

Michael

On Tue, Aug 18, 2009 at 12:51 PM, Huming Wu<huming.wu@gmail.com> wrote:
> Here is the log4j setting (yes, it is just INFO):
> log4j.rootLogger=INFO,stdout,R
>
> I am not sure why the latency dropped during last 24 hours. One stats
> I can see (from other reports) is that disk reads dropped 80% (reads
> per sec) in last 24 hour which may explain the drop (less disk read).
>
> I wanted to bring up this discussion on performance and ultimately
> this is what matters the most to a production system (at least for
> us). And I'd be glad to contribute (still fairly new to Cassandra
> though) in this area. I hoped someone had done some tests and
> therefore numbers can be cross examined. Performance numbers are
> always dependent on the test data. I provided the data profile in my
> original email already.
>
> By the way to measure the performance, I inserted timing code to
> get_slice and batch_insert, for example, for get_slice:
>
> public List<ColumnOrSuperColumn> get_slice(...)
> {
> long t0 = System.currentTimeMillis();
> ....
>
> long lat = System.currentTimeMillis() - t0)/(float)1000.0
> return col;
> }
> And report this latency for every call to our in-house metrics system.
> So this is server side report (not client).
>
> To me, for the sustained read, cassandra uses too much cpu. Anyone has
> seen the same thing?
>
> Thanks,
> Huming
>

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