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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: mmap
Date Thu, 15 Jul 2010 21:52:39 GMT
On Thu, Jul 15, 2010 at 3:56 PM, Carlos Alvarez <cbalvarez@gmail.com> wrote:
> On Thu, Jul 15, 2010 at 2:01 PM, Jonathan Ellis <jbellis@gmail.com> wrote:
>> The main problem is not the syscall so much as Java insisting on
>> zeroing out any buffer you create, which is a big hit to performance
>> when you're allocating buffers for file i/o on each request instead of
>> just mmaping things.  Re-using those buffers would be possible but
>> difficult; I think using mlockall to "fix" the mmap approach is more
>> promising.
>
> Sorry if it is a silly question, but what would be the approach? issue
> a mlockall with the current set (MLC_CURRENT) before mmap the files?

right

> Did someone have an opinion on that
> http://delivery.acm.org/10.1145/1820000/1814327/p20-kamp.pdf?key1=1814327&key2=0207229721&coll=GUIDE&dl=GUIDE&CFID=97156491&CFTOKEN=66732025
> ?.
>
> Do you think it could be useful for cassandra to arrange things in the
> files in order to try to have that kind of 'page afinity' in the data
> and minimize the page faults trasversing the data?

that's exactly what the sstable index design is already doing

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

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