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


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:
>             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|]

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