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https://issues.apache.org/jira/browse/CASSANDRA-6746?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13944821#comment-13944821
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Benedict commented on CASSANDRA-6746:
-------------------------------------
@enigmacurry looks kosher.
It won't be eliminating any drop at the start, it is just moving the timing of
the drops (and making them shorter). I think we should rename this ticket to
"compaction destroys page cache" and split out a new ticket for [~xedin]'s
changes ("page cache population is suboptimal") which may be sensible in
principle. In practice, moving the WILLNEED into the getSegment() call is
dangerous as the segment is used past the initial 64Kb, and if we rely on
ourselves only for read-ahead this could result in very substandard performance
for larger rows. We also probably want to only WILLNEED the actual size of the
buffer we expect to read for compressed files. But this was only a
proof-of-concept, and in principle the idea is probably sound.
> 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-buffered-io-tweaks.png,
> 6746-patched.png, 6746.blockdev_setra.full.png,
> 6746.blockdev_setra.zoomed.png, 6746.buffered_io_tweaks.logs.tar.gz,
> 6746.buffered_io_tweaks.write-flush-compact-mixed.png,
> 6746.buffered_io_tweaks.write-read-flush-compact.png, 6746.txt,
> buffered-io-tweaks.patch, 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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