I have a program to stress test Cassandra. What it does is remove/insert rows with a small set of row keys as fast as possible. Two CFs are involved. When I test against C* 1.2.3 with default configurations, it ran for 24 hours and C* doesn't having any issue. However after I upgraded to C* 2.0.1, C* crashes on OOM within 1-2 minutes. I can consistently reproduce this.
I built C* from the source and found out the last good changeset is cfa097cdd5e28d7fe8204248e246a1fae226d2c0. As soon as I include the next changeset 1e0d9513b748fae4ec0737283da71c65e9272102, C* starts to crash. What's interesting is although it seems the change was reverted by fc1a7206fe15882fd64e7ba8eb68ba9dc320275f. C* built from fc1a7206fe15882fd64e7ba8eb68ba9dc320275f has the same problem - OOM within minutes.
I didn't test against the official 2.0.0. But the C* built from 03045ca22b11b0e5fc85c4fabd83ce6121b5709b seems OK. I assume that's what 2.0.0 is.
I use default configurations in all cases. I didn't tune anything.