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From Geoffrey Hendrey <geoff_hend...@yahoo.com>
Subject Re: Derby speedup by not using page caches?
Date Sun, 01 Mar 2009 01:13:24 GMT

I think I saw that in java 7 they are allowing ByteBuffer to accept a long. This means no
more 2gb limit for memory mapped io (it was never 4 gb because ByteBuffer pukes on negative
integers).

I've been astonished by how fast memory mapped io is in java. So thumbs up for memory mapped
derby pages.

On Feb 28, 2009, at 5:00 PM, Kurt Huwig <k.huwig@iku-ag.de> wrote:

Hi,

I just stumbled upon this page

http://varnish.projects.linpro.no/wiki/ArchitectNotes

where the author writes that caching of disk files within the application hurts 
performance on current operating systems. Right now, the data is in memory at 
least twice: the OS cache and the Derby cache which sounds suboptimal. And it 
gets worse if the OS decides to swap out the application's cache.

With the widespread use of 64-bit machines and therefore a huge address space, 
is it possible to (optionally) disable the page cache and use memory mapped 
files instead? This would also solve the "how much page cache to use?"-problem. 
Sure on 32 bit you are limited to a database size of 1-3 GB but you should 
still see the speedup, especially on low memory systems.
-- 
Kurt
GnuPG 1024D/99DD9468 64B1 0C5B 82BC E16E 8940  EB6D 4C32 F908 99DD 9468


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