sankalp kohli commented on CASSANDRA-12668:

"Lower throughput != unusable"

The cluster was working in 2.0 and is no longer working in 2.1. That is 
unusable. Applications needs a certain throughput otherwise they will have ever 
increasing backlog. 

"Everything is about trade-offs, as was the swapping of the data structure in 
the first place. There's rarely a 100% free lunch."
The tradeoff where a use case is made unusable is not a trade off we should 

"Just some fairly broad qualitative/correlative statements."
These are not statements but practical experience with a cluster which has been 
made unusable in 2.1. I will give out more information that you are asking.  

> 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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