From mboxrd@z Thu Jan  1 00:00:00 1970
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Date: Thu, 17 Jul 2008 12:04:07 +0200
From: Kernel Panic <cinap_lenrek@gmx.de>
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To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
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Subject: Re: [9fans] 8 cores
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Charles Forsyth wrote:
>> I could imagine that databases use mmap() havily
>>
>
> it's a little mystery for me why they would do that since it's slower (or ought to be),
> because the trap path and fault recovery must do more work than syscall (perhaps much more).
> it's also difficult then to optimise the replacement strategy for the application
> without madvise calls (and you trust those implicitly?) but those are system calls that cost time.
>
>
makes sense of course...

but at least mysql uses mmap() for some table types as a caching mechanism.
http://www.mysqlperformanceblog.com/2006/05/26/myisam-mmap-feature-51/

this may just be an exception and real databases use read()/write() syscalls
and implement the caching themself.

but where should i know... i dont need/use databases and have not looked
at the sourcecode of one.

cinap