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https://issues.apache.org/jira/browse/CASSANDRA-6746?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13938214#comment-13938214
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Ryan McGuire edited comment on CASSANDRA-6746 at 3/17/14 7:04 PM:
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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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