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From "sankalp kohli (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-12668) Memtable Contention in 2.1
Date Mon, 19 Sep 2016 22:46:20 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-12668?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15504919#comment-15504919
] 

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 make. 


"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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