You probably want to look at your bloom filters.  Be forewarned though, they're difficult to change; changes to bloom filter settings only apply to new SSTables, so they might not be noticeable until a few compactions have taken place.

If that is your issue, and your usage model fits it, a good alternative to the slow propagation of higher miss rates is to switch to LCS (which doesn't use bloom filters), which won't require you to make the jump to 1.2.

On Fri, Feb 15, 2013 at 4:06 AM, Reik Schatz <> wrote:

recently we are hitting some OOM: Java heap space, so I was investigating how the heap is used in Cassandra 1.2+

We use the calculated 4G heap. Our cluster is 6 nodes, around 750 GB data and a replication factor of 3. Row cache is disabled. All key cache and memtable settings are left at default.

Is the primary key index kept in heap memory? We have a bunch of keyspaces and column families.



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