Benedict commented on CASSANDRA-12668:

Come on, let's avoid hyperbole.

Lower throughput != unusable, and if you were to reduce the size of your 
memtables the increased GC burden would probably be coped with too.  Everything 
is about trade-offs, as was the swapping of the data structure in the first 
place.  There's rarely a 100% free lunch.

Still, much more information is needed before anything informative can be said. 
 You've still given very few details; we still have nothing about the size of 
the partitions, their number, the rate of updates (total and per partition), 
the size of the datums, the total size provided for the memtables.  The 
configuration parameters such as flush queue size, memtable_cleanup_threshold 
and concurrent_writes.  No profiling information, no heap numbers.  Just some 
fairly broad qualitative/correlative statements.

> Memtable Contention in 2.1
> --------------------------
>                 Key: CASSANDRA-12668
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-12668
>             Project: Cassandra
>          Issue Type: Bug
>            Reporter: sankalp kohli
> We added a new Btree implementation in 2.1 which causes write performance to 
> go down in Cassandra if there is  lot of contention in the memtable for a CQL 
> partition. Upgrading a cluster from 2.0 to 2.1 with contention causes the 
> cluster to fall apart due to GC. We tried making the defaults added in 
> CASSANDRA-7546 configurable but that did not help. Is there anyway to fix 
> this issue?

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