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From Benedict Elliott Smith <belliottsm...@datastax.com>
Subject Re: [jira] [Commented] (CASSANDRA-6746) Reads have a slow ramp up in speed
Date Thu, 27 Feb 2014 21:06:49 GMT
I've been investigating this, but a bit slowly as was looking in the wrong
place. I haven't yet confirmed, but I have a strong suspicion of the
problem. Could you confirm the total physical memory on the nodes? If 8gb
or less, try applying the not yet committed patches in CASSANDRA-6692
(atomic b tree improvements), and setting the memtable_cleanup_threshold to
0.2, if you are looking at this today. I suspect it will fix it, although
if so it doesn't quite adequately explain the behaviour exactly. If you let
me know the cluster you're using I can test the same environment to make
sure I'm testing like for like as well.
On 27 Feb 2014 20:58, "Ryan McGuire (JIRA)" <jira@apache.org> wrote:

>
>     [
> https://issues.apache.org/jira/browse/CASSANDRA-6746?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13915038#comment-13915038]
>
> Ryan McGuire commented on CASSANDRA-6746:
> -----------------------------------------
>
> I tried re-running this with a 'nodetool flush' on each node after it's
> done with the write. It looked the same as above. I'm running a test with a
> 5 minute wait between the write and read to see if that causes a change.
>
> > Reads have a slow ramp up in speed
> > ----------------------------------
> >
> >                 Key: CASSANDRA-6746
> >                 URL:
> https://issues.apache.org/jira/browse/CASSANDRA-6746
> >             Project: Cassandra
> >          Issue Type: Bug
> >          Components: Core
> >            Reporter: Ryan McGuire
> >            Assignee: Benedict
> >              Labels: performance
> >             Fix For: 2.1 beta2
> >
> >         Attachments: 2.1_vs_2.0_read.png
> >
> >
> > On a physical four node cluister I am doing a big write and then a big
> read. The read takes a long time to ramp up to respectable speeds.
> > !2.1_vs_2.0_read.png!
> > [See data here|
> http://ryanmcguire.info/ds/graph/graph.html?stats=stats.2.1_vs_2.0_vs_1.2.retry1.json&metric=interval_op_rate&operation=stress-read&smoothing=1
> ]
>
>
>
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