It depends on a lot of things: schema size, caches, work load etc. If your are just starting out I would recommend using a machine with 8gb or 16gb total ram. By default cassandra will take about 4gb or 8gb (respectively) for the JVM.
Once you have a feel for how things work you should be able to estimate the resources your application will need. Hope that helps. ----------------- Aaron Morton Freelance Developer @aaronmorton http://www.thelastpickle.com On 13/04/2012, at 2:19 AM, Vasileios Vlachos wrote: > Hello Aaron, > > Thank you for getting back to me. > > I will change to m1.large first to see how long it will take Cassandra node > to die (if at all). If again not happy I will try more memory. I just want to > test it step by step and see what the differences are. I will also change the > cassandra-env file back to defaults. > > Is there an absolute minimum requirement for Cassandra in terms of memory? I > might be wrong, but from my understanding we shouldn't have any problems > given the amount of data we store per day (currently approximately 2-2.5G / > day). > > Thank you in advance, > > Bill > > > On Wed, Apr 11, 2012 at 7:33 PM, aaron morton <aa...@thelastpickle.com> wrote: >> 'system_memory_in_mb' (3760) and the 'system_cpu_cores' (1) according to our >> nodes' specification. We also changed the 'MAX_HEAP_SIZE' to 2G and the >> 'HEAP_NEWSIZE' to 200M (we think the second is related to the Garbage >> Collection). > It's best to leave the default settings unless you know what you are doing > here. > >> In case you find this useful, swap is off and unevictable memory seems to be >> very high on all 3 servers (2.3GB, we usually observe the amount of >> unevictable memory on other Linux servers of around 0-16KB) > Cassandra locks the java memory so it cannot be swapped out. > >> The problem is that the node we hit from our thrift interface dies regularly >> (approximately after we store 2-2.5G of data). Error message: >> OutOfMemoryError: Java Heap Space and according to the log it in fact used >> all of the allocated memory. > The easiest solution will be to use a larger EC2 instance. > > People normally use an m1.xlarge with 16Gb of ram (you would also try an > m1.large). > > If you are still experimenting I would suggest using the larger instances so > you can make some progress. Once you have a feel for how things work you can > then try to match the instances to your budget. > > Hope that helps. > > ----------------- > Aaron Morton > Freelance Developer > @aaronmorton > http://www.thelastpickle.com > > On 11/04/2012, at 1:54 AM, Vasileios Vlachos wrote: > >> Hello, >> >> We are experimenting a bit with Cassandra lately (version 1.0.7) and we seem >> to have some problems with memory. We use EC2 as our test environment and we >> have three nodes with 3.7G of memory and 1 core @ 2.4G, all running Ubuntu >> server 11.10. >> >> The problem is that the node we hit from our thrift interface dies regularly >> (approximately after we store 2-2.5G of data). Error message: >> OutOfMemoryError: Java Heap Space and according to the log it in fact used >> all of the allocated memory. >> >> The nodes are under relatively constant load and store about 2000-4000 row >> keys a minute, which are batched through the Trift interface in 10-30 row >> keys at once (with about 50 columns each). The number of reads is very low >> with around 1000-2000 a day and only requesting the data of a single row >> key. The is currently only one used column family. >> >> The initial thought was that something was wrong in the cassandra-env.sh >> file. So, we specified the variables 'system_memory_in_mb' (3760) and the >> 'system_cpu_cores' (1) according to our nodes' specification. We also >> changed the 'MAX_HEAP_SIZE' to 2G and the 'HEAP_NEWSIZE' to 200M (we think >> the second is related to the Garbage Collection). Unfortunately, that did >> not solve the issue and the node we hit via thrift keeps on dying regularly. >> >> In case you find this useful, swap is off and unevictable memory seems to be >> very high on all 3 servers (2.3GB, we usually observe the amount of >> unevictable memory on other Linux servers of around 0-16KB) (We are not >> quite sure how the unevictable memory ties into Cassandra, its just >> something we observed while looking into the problem). The CPU is pretty >> much idle the entire time. The heap memory is clearly being reduced once in >> a while according to nodetool, but obviously grows over the limit as time >> goes by. >> >> Any ideas? Thanks in advance. >> >> Bill > >
