What version of cassandra are you using ?
What are the JVM settings? (check with ps aux | grep cassandra)


OOM in cassandra 1.2+ is rare but there is also https://issues.apache.org/jira/browse/CASSANDRA-5706 and https://issues.apache.org/jira/browse/CASSANDRA-6087

One instance of "org.apache.cassandra.db.ColumnFamilyStore" loaded by "sun.misc.Launcher$AppClassLoader @ 0x613e1bdc8" occupies 984,094,664 (11.64%) bytes.
938MB is a bit of memory, the CFS and data tracker are dealing with the memtable. This may indicate things are not being flushed from memory correctly. 

•java.lang.Thread @ 0x73e1f74c8 CompactionExecutor:158 - 839,225,000 (9.92%) bytes.
•java.lang.Thread @ 0x717f08178 MutationStage:31 - 809,909,192 (9.58%) bytes.
•java.lang.Thread @ 0x717f082c8 MutationStage:5 - 649,667,472 (7.68%) bytes.
•java.lang.Thread @ 0x717f083a8 MutationStage:21 - 498,081,544 (5.89%) bytes.
•java.lang.Thread @ 0x71b357e70 MutationStage:11 - 444,931,288 (5.26%) bytes.
maybe very big rows and/or very big mutations. 

hope that helps. 

-----------------
Aaron Morton
New Zealand
@aaronmorton

Co-Founder & Principal Consultant
Apache Cassandra Consulting
http://www.thelastpickle.com

On 15/11/2013, at 12:34 pm, Mike Koh <defmikekoh@gmail.com> wrote:

I am investigating Java Out of memory heap errors. So I created an .hprof file and loaded it into Eclipse Memory Analyzer Tool which gave some "Problem Suspects".

First one looks like:
----
One instance of "org.apache.cassandra.db.ColumnFamilyStore" loaded by "sun.misc.Launcher$AppClassLoader @ 0x613e1bdc8" occupies 984,094,664 (11.64%) bytes. The memory is accumulated in one instance of "org.apache.cassandra.db.DataTracker$View" loaded by "sun.misc.Launcher$AppClassLoader @ 0x613e1bdc8".
----

If I click around into the verbiage, I believe I can pick out the name of a column family but that is about it. Can someone explain what the above means in more detail and if it is indicative of a problem?


Next one looks like:
-----
•java.lang.Thread @ 0x73e1f74c8 CompactionExecutor:158 - 839,225,000 (9.92%) bytes.
•java.lang.Thread @ 0x717f08178 MutationStage:31 - 809,909,192 (9.58%) bytes.
•java.lang.Thread @ 0x717f082c8 MutationStage:5 - 649,667,472 (7.68%) bytes.
•java.lang.Thread @ 0x717f083a8 MutationStage:21 - 498,081,544 (5.89%) bytes.
•java.lang.Thread @ 0x71b357e70 MutationStage:11 - 444,931,288 (5.26%) bytes.
------
If I click into the verbiage, they above Compaction and Mutations all seem to be referencing the same column family. Are the above related? Is there a way I can tell more exactly what is being compacted and/or mutated more specifically than which column family?