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https://issues.apache.org/jira/browse/CASSANDRA-1214?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12881226#action_12881226
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James Golick commented on CASSANDRA-1214:
-----------------------------------------
I have tried many levels of swappiness (including 0) without any change in
behaviour. Additionally, I haven't seen much if any change in performance with
standard IO.
Continuing to iterate on the mmap code might be a good idea. But, it's the
wrong default. Especially now that we've agreed that it is currently broken.
It's possible that it may be a sensible default in the future, but right now,
it's not a good choice for production (in most cases).
> Make standard IO the default
> ----------------------------
>
> Key: CASSANDRA-1214
> URL: https://issues.apache.org/jira/browse/CASSANDRA-1214
> Project: Cassandra
> Issue Type: Bug
> Affects Versions: 0.7
> Reporter: James Golick
>
> 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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