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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 19:58:21 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-12668?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15504501#comment-15504501
] 

sankalp kohli commented on CASSANDRA-12668:
-------------------------------------------

By "always synchronous" I assume you mean always locking instead of using CAS? 

We did a test where you always write to a few CQL partition simultaneous to create contention.
We have seen 2.0 has a higher throughput than 2.1 and looking at allocation points to this
memtable issue.

Then we made the configuration changes added in  7546 to always lock and that reduced the
throughput. 

Looking at the heap dumps did not point that memtable is smaller in 2.1 vs 2.0. So I dont
think this is an issue. 

Apart from the testing, the only clusters this is an issue is where we have contention and
hence this is change is an issue. 

> 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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