I have the same configuration and I recently change my cassandra-sh.yaml to :
MAX_HEAP_SIZE="4G" HEAP_NEWSIZE="200M" I guess it depends on how much you use the cache (which is now in the off-heap memory). I don't use row cache and use the default key cache size. I have no more memory pressure nor OOM. I think that if your off-heap memory is unused, it's better enlarging the heap (with a max limit of 8GB) Hope this will help. Alain 2012/8/21 Tamar Fraenkel <ta...@tok-media.com> > Hi! > I have a question regarding Cassandra heap size. > Cassandra calculates heap size in cassandra-env.sh according to the > following algorythm > # set max heap size based on the following > # max(min(1/2 ram, 1024MB), min(1/4 ram, 8GB)) > # calculate 1/2 ram and cap to 1024MB > # calculate 1/4 ram and cap to 8192MB > # pick the max > > So, for > system_memory_in_mb=7468 > half_system_memory_in_mb=3734 > quarter_system_memory_in_mb=1867 > This will result in > max(min(3734,1024), min(1867,8000)) = max(1024,1867)=*1867MB* or in other > words 1/4 of RAM. > > In http://www.datastax.com/docs/1.0/operations/tuning it says: "Cassandra's > default configuration opens the JVM with a heap size of 1/4 of the > available system memory (or a minimum 1GB and maximum of 8GB for systems > with a very low or very high amount of RAM). Heapspace should be a minimum > of 1/2 of your RAM, but a maximum of 8GB. The vast majority of deployments > do not benefit from larger heap sizes because (in most cases) the ability > of Java 6 to gracefully handle garbage collection above 8GB quickly > diminishes." > *If I understand this correctly, this means it is better if my heap size > will be 1/2 of RAM, 3734MB.* > I am running on EC2 m1.large instance (7.5 GB memory, 4 EC2 Compute Units > (2 virtual cores with 2 EC2 Compute Units each)). > My system seems to be suffering from lack of memory, and I should probably > increase heap or (and?) reduce key cache size. > > Would you recommend changing the heap to half RAM? > > If yes, should I hard-code it in acassandra-env.sh? > > Thanks! > > *Tamar Fraenkel * > Senior Software Engineer, TOK Media > > [image: Inline image 1] > > ta...@tok-media.com > Tel: +972 2 6409736 > Mob: +972 54 8356490 > Fax: +972 2 5612956 > > > >
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