There appears to be a GC issue due to memory pressure in the 0.6 branch. You can see this by starting the server and performing many inserts. Quickly the jvm will consume most of its heap, and pauses for stop-the-world GC will begin. With verbose GC turned on, this can be observed as follows:
[GC [ParNew (promotion failed): 79703K->79703K(84544K), 0.0622980 secs][CMS[CMS-concurrent-mark: 3.678/5.031 secs] [Times: user=10.35 sys=4.22, real=5.03 secs]
(concurrent mode failure): 944529K->492222K(963392K), 2.8264480 secs] 990745K->492222K(1047936K), 2.8890500 secs] [Times: user=2.90 sys=0.04, real=2.90 secs]
After enough inserts (around 75-100 million) the server will GC storm and then OOM.
jbellis and I narrowed this down to patch 0001 in
CASSANDRA-724. Switching LBQ with ABQ made no difference, however using batch mode instead of periodic for the commitlog does prevent the issue from occurring. The attached screenshot shows the heap usage in jconsole first when the issue is exhibiting, a restart, and then the same amount of inserts when it does not.