You don't GC storm without legitimately having a too-full heap. It's normal to see occasional full GCs from fragmentation, but that will actually compact the heap and everything goes back to normal IF you had space actually freed up.
You say you've played w/ memtable size but that would still be my bet. Most people severely underestimate how much space this takes (10x in memory over serialized size), which will bite you when you have lots of CFs defined. Otherwise, force a heap dump after a full GC and take a look to see what's referencing all the memory. On Fri, May 6, 2011 at 12:25 PM, Serediuk, Adam <adam.sered...@serialssolutions.com> wrote: > We're troubleshooting a memory usage problem during batch reads. We've spent > the last few days profiling and trying different GC settings. The symptoms > are that after a certain amount of time during reads one or more nodes in the > cluster will exhibit extreme memory pressure followed by a gc storm. We've > tried every possible JVM setting and different GC methods and the issue > persists. This is pointing towards something instantiating a lot of objects > and keeping references so that they can't be cleaned up. > > Typically nothing is ever logged other than the GC failures however just now > one of the nodes emitted logs we've never seen before: > > INFO [ScheduledTasks:1] 2011-05-06 15:04:55,085 StorageService.java (line > 2218) Unable to reduce heap usage since there are no dirty column families > > We have tried increasing the heap on these nodes to large values, eg 24GB and > still run into the same issue. We're running 8GB of heap normally and only > one or two nodes will ever exhibit this issue, randomly. We don't use key/row > caching and our memtable sizing is 64mb/0.3. Larger or smaller memtables make > no difference in avoiding the issue. We're on 0.7.5, mmap, jna and jdk > 1.6.0_24 > > We've somewhat hit the wall in troubleshooting and any advice is greatly > appreciated. > > -- > Adam > -- Jonathan Ellis Project Chair, Apache Cassandra co-founder of DataStax, the source for professional Cassandra support http://www.datastax.com
