[jira] [Commented] (CASSANDRA-10249) Reduce over-read for standard disk io by 16x

["Chris Burroughs (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-10249?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14727278#comment-14727278 ] 

Chris Burroughs commented on CASSANDRA-10249:
---------------------------------------------

This isn't a 2.1 regression right?  It's been 65536 since 2011 or so.

> Reduce over-read for standard disk io by 16x
> --------------------------------------------
>
>                 Key: CASSANDRA-10249
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-10249
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Albert P Tobey
>             Fix For: 2.1.x
>
>         Attachments: patched-2.1.9-dstat-lvn10.png, stock-2.1.9-dstat-lvn10.png, yourkit-screenshot.png
>
>
> On read workloads, Cassandra 2.1 reads drastically more data than it emits over the network. This causes problems throughput the system by wasting disk IO and causing unnecessary GC.
> I have reproduce the issue on clusters and locally with a single instance. The only requirement to reproduce the issue is enough data to blow through the page cache. The default schema and data size with cassandra-stress is sufficient for exposing the issue.
> With stock 2.1.9 I regularly observed anywhere from 300:1  to 500 disk:network ratio. That is to say, for 1MB/s of network IO, Cassandra was doing 300-500MB/s of disk reads, saturating the drive.
> After applying this patch for standard IO mode https://gist.github.com/tobert/10c307cf3709a585a7cf the ratio fell to around 100:1 on my local test rig. Latency improved considerably and GC became a lot less frequent.
> I tested with 512 byte reads as well, but got the same performance, which makes sense since all HDD and SSD made in the last few years have a 4K block size (many of them lie and say 512).
> I'm re-running the numbers now and will post them tomorrow.



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