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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-6746) Reads have a slow ramp up in speed
Date Thu, 13 Mar 2014 18:23:47 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-6746?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13933805#comment-13933805
] 

Jonathan Ellis commented on CASSANDRA-6746:
-------------------------------------------

The 2635 issue description is from a production cluster.  ("We've applied this patch locally
in order to turn of page skipping...  It's better than completely disabling DONTNEED because
the cache skipping does make sense and has no relevant (that I can see) detrimental effects
in some cases, like when dumping caches.")

This replaced an approach of DONTNEEDing the old sstables, which would crater read requests
since old sstables will still be in use during compaction before the new ones are completely
live.

> 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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