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From "sankalp kohli (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-12668) Memtable Contention in 2.1
Date Mon, 19 Sep 2016 21:08:21 GMT


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:
>             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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