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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: Minimizing the impact of compaction on latency and throughput
Date Tue, 13 Jul 2010 13:26:31 GMT
On Tue, Jul 13, 2010 at 6:18 AM, Terje Marthinussen
<tmarthinussen@gmail.com> wrote:
> Due to the need for doing data alignment in the application itself (you are
> bypassing all the OS magic here), there is really nothing portable about
> O_DIRECT.

I'm totally fine with saying "Here's a JNI library for Linux [or even
Linux version >= 2.6.X]" since that makes up 99% of our production
deployments, and leaving the remaining 1% with the status quo.

> O_DIRECT also bypasses the cache completely

Right, that's the idea. :)

> O_DIRECT was made to solve HW performance limitation on servers 10+ years
> ago. It is far from an ideal solution today (but until stuff like fadvice is
> implemented properly, somewhat unavoidable)

Exactly: it the fadvise mode that would actually be useful to us, is a
no-op and not likely to change soon. A bit of history:
http://www.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.18-rc3/2.6.18-rc3-mm1/broken-out/fadvise-make-posix_fadv_noreuse-a-no-op.patch

-- 
Jonathan Ellis
Project Chair, Apache Cassandra
co-founder of Riptano, the source for professional Cassandra support
http://riptano.com

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