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From "Aleksey Yeschenko (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-10249) Make buffered read size configurable
Date Wed, 11 Nov 2015 18:48:11 GMT


Aleksey Yeschenko commented on CASSANDRA-10249:

[~tobert] Sure, I'm okay with committing to just 2.1 and 2.2. The provided 2.1 patch doesn't
merge with 2.2, though, so I need that version.


> Make buffered read size configurable
> ------------------------------------
>                 Key: CASSANDRA-10249
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Albert P Tobey
>            Assignee: Albert P Tobey
>             Fix For: 2.1.x, 2.2.x, 3.0.x
>         Attachments: Screenshot 2015-09-11 09.32.04.png, Screenshot 2015-09-11 09.34.10.png,
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
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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