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<[email protected]> 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 >
