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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-6746) Reads have a slow ramp up in speed
Date Fri, 28 Feb 2014 16:32:22 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-6746?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13915949#comment-13915949
] 

Jonathan Ellis commented on CASSANDRA-6746:
-------------------------------------------

bq. The result being that we do not "skip IO cache" in 2.0.

Well, we do if JNA is installed -- the difference is that we don't ship JNA out of the box.
:)

bq. if we're compacting live data we will actively destroy the page cache when the OS listens
stringently to the DONTNEED

The behavior on flush and compaction is actually slightly different:

* on flush, we actively DONTNEED unless populate_io_cache_on_flush is enabled [false by default]
* on compact, we WILLNEED partitions that are "hot" in the key cache, unless compaction_preheat_key_cache
is disabled [true by default].  Nothing is WONTNEEDed.

We should probably create tables for short tests with populate_io_cache_on_flush enabled.
 /cc [~enigmacurry] [~mshuler]


> 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
>
>
> 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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