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From "Benedict (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (CASSANDRA-6746) Reads have a slow ramp up in speed
Date Sat, 15 Mar 2014 01:31:45 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-6746?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13935923#comment-13935923
] 

Benedict edited comment on CASSANDRA-6746 at 3/15/14 1:31 AM:
--------------------------------------------------------------

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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