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https://issues.apache.org/jira/browse/CASSANDRA-1214?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12992350#comment-12992350
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Yang Yang commented on CASSANDRA-1214:
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Jonathan:
why is MCL_CURRENT chosen? I thought you would want to use MCL_FUTURE (ignoring
the discussion above that these 2 seem to have the same value).
with MCL_CURRENT, supposedly SSTables that you mmap() later will still have the
possibility to be paged out. or maybe I am not understanding it correctly?
Thanks
Yang
> Force linux to not swap the JVM
> -------------------------------
>
> Key: CASSANDRA-1214
> URL: https://issues.apache.org/jira/browse/CASSANDRA-1214
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Reporter: James Golick
> Assignee: Jonathan Ellis
> Fix For: 0.6.5, 0.7 beta 2
>
> Attachments: 1214-v3.txt, 1214-v4.txt, Read Throughput with mmap.jpg,
> mlockall-jna.patch.txt, trunk-1214.txt
>
>
> The way mmap()'d IO is handled in cassandra is dangerous. It allocates
> potentially massive buffers without any care for bounding the total size of
> the program's buffers. As the node's dataset grows, this *will* lead to
> swapping and instability.
> This is a dangerous and wrong default for a couple of reasons.
> 1) People are likely to test cassandra with the default settings. This issue
> is insidious because it only appears when you have sufficient data in a
> certain node, there is absolutely no way to control it, and it doesn't at all
> respect the memory limits that you give to the JVM.
> That can all be ascertained by reading the code, and people should certainly
> do their homework, but nevertheless, cassandra should ship with sane defaults
> that don't break down when you cross some magic unknown threshold.
> 2) It's deceptive. Unless you are extremely careful with capacity planning,
> you will get bit by this. Most people won't really be able to use this in
> production, so why get them excited about performance that they can't
> actually have?
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