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From "Ryan McGuire (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (CASSANDRA-6746) Reads have a slow ramp up in speed
Date Mon, 17 Mar 2014 19:05:45 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-6746?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13938214#comment-13938214
] 

Ryan McGuire edited comment on CASSANDRA-6746 at 3/17/14 7:04 PM:
------------------------------------------------------------------

Playing around with 'blockdev --setra' does have a rather dramatic effect.

Here's four runs, with read ahead set to 0, 128, 256, and 4096:

!6746.blockdev_setra.full.png!

The setting for 0 dwarfs the other results, so here it is zoomed in on just 128, 256, and
4096:

!6746.blockdev_setra.zoomed.png!

[raw data is here|http://riptano.github.io/cassandra_performance/graph/graph.html?stats=stats.6746.blockdev_readahead.json&metric=op_rate&operation=read&smoothing=1]

The double bump in the run for 4096 is something that [~benedict] and I have seen on other
runs before.


was (Author: enigmacurry):
Playing around with 'blockdev --setra' does have a rather dramatic effect.

Here's four runs, with read ahead set to 0, 128, 256, and 4096:

!6746.blockdev_setra.full.png!

The setting for 0 dwarfs the other results, so here it is zoomed in on just 128, 256, and
4096:

!6746.blockdev_setra.zoomed.png!

[raw data is here|http://riptano.github.io/cassandra_performance/graph/graph.html?stats=stats.6746.blockdev_readahead.json&metric=op_rate&operation=read&smoothing=1]

> 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.blockdev_setra.full.png,
6746.blockdev_setra.zoomed.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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