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From "Edward Capriolo (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-6746) Reads have a slow ramp up in speed
Date Sun, 16 Mar 2014 07:26:48 GMT


Edward Capriolo commented on CASSANDRA-6746:

FWIW, I'd be okay with dropping mmap mode entirely since compression has been the default
for almost two years now.
Are you implying that because compression is the default no one uses uncompressed tables any
more? If so I disagree. In cases with small rows 1-10 columns compression can hurt your performance.
I am assuming what happens is de serializing compressed blocks 4 k blocks when rows are small
creates much more young gen and ends up being a bottleneck. Several operators have told me
they do not use compression on high read column families. 

> Reads have a slow ramp up in speed
> ----------------------------------
>                 Key: CASSANDRA-6746
>                 URL:
>             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.txt, cassandra-2.0-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|]

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