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https://issues.apache.org/jira/browse/CASSANDRA-6746?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13935923#comment-13935923
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Benedict edited comment on CASSANDRA-6746 at 3/15/14 1:31 AM:
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bq. I'm not sure how are you doing that, can you elaborate? it's only possible
to set POSIX_FADV_RANDOM when disk_access_mode is "standard" in yaml, by
default we use we do mmap which requires us to do madvice for RANDOM instead of
fadvice, so your slowdown is kind of expected there.
-Good point, this is exactly what I was doing.-
No, I was using fadvise, assuming the functions are correctly named. We use
fadvise DONTNEED, and I simply used POSIX_FADV_RANDOM.
Sounds like we're agreeing with the other stuff already :-)
was (Author: benedict):
bq. I'm not sure how are you doing that, can you elaborate? it's only possible
to set POSIX_FADV_RANDOM when disk_access_mode is "standard" in yaml, by
default we use we do mmap which requires us to do madvice for RANDOM instead of
fadvice, so your slowdown is kind of expected there.
Good point, this is exactly what I was doing.
Sounds like we're agreeing with the other stuff already :-)
> 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, 6746-patched.png, 6746.txt,
> cassandra-2.0-bdplab-trial-fincore.tar.bz2,
> cassandra-2.1-bdplab-trial-fincore.tar.bz2
>
>
> 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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