sankalp kohli commented on CASSANDRA-12668:

The assertions are from real cluster as well but we also did the same work in 
testing as well. 

"Of course, it may well also be that for your test case it is inherently worse; 
not every use case can be improved."
I agree you cannot improve every use case but here we have made a use case 
worse here. 

The reason in lower thought-put is due to locking added in 7546. But the root 
cause is still still the memtable Btree change. 

I will try with different fan-factor and see if it helps.  

> 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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