Are you using cassandra's caching? If you are then you will need to play around with the RAM setting to find a sweet spot. A low hit rate on the cache (which is counter productive anyway) will cause more GC. A high hit rate, less GC.
If you are not caching, no need to use a large heap as the OS will do a fine job of caching the data files for you. And in fact I would run with a smaller'ish heap to give the OS more room - how much depends on a variety of things (how many column families, how often repair, write/read ratio) - so testing is the best course of action On 10/20/11 6:38 AM, "Maxim Potekhin" <potek...@bnl.gov> wrote: >Hello Aaron, > >I happen to have 48GB on each machines I use in the cluster. Can I >assume that I can't really use all of this memory productively? Do you >have any suggestion related to that? Can I run more than one instance on >Cassandra on the same box (using different ports) to take advantage of >this memory, assuming the disk has enough bandwidth? > >Thanks, >Maxim > >On 9/25/2011 11:37 AM, aaron morton wrote: >> It does seem long and will be felt by your application. >> >> Are you running a 47GB heap ? Most peeps seem to think 8 to 12 is about >>the viable maximum. >> >> Cheers >> >> ----------------- >> Aaron Morton >> Freelance Cassandra Developer >> @aaronmorton >> http://www.thelastpickle.com >> >> On 25/09/2011, at 7:14 PM, Yang wrote: >> >>> I see the following in my GC log >>> >>> 1910.513: [GC [1 CMS-initial-mark: 2598619K(26214400K)] >>> 13749939K(49807360K), 6.0696680 secs] [Times: user=6.10 sys=0.00, >>> real=6.07 secs] >>> >>> so there is a stop-the-world period of 6 seconds. does this sound bad >>> ? or 6 seconds is OK and we should expect the built-in >>> fault-tolerance of Cassandra handle this? >>> >>> Thanks >>> Yang >
