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libuv - posix_fadvise() on windows
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Liam  
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 More options Nov 27 2011, 5:30 pm
From: Liam <networkimp...@gmail.com>
Date: Sun, 27 Nov 2011 14:30:25 -0800 (PST)
Local: Sun, Nov 27 2011 5:30 pm
Subject: libuv - posix_fadvise() on windows
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posix_fadvise(fd, start, end, advice) allows one to specify that a
file should be omitted from the filesystem cache after a read(), among
other things.

http://www.kernel.org/doc/man-pages/online/pages/man2/posix_fadvise.2...

I've added a libuv issue: https://github.com/joyent/libuv/issues/256

Anyone have insights on Windows APIs for these features?

Should libuv provide an fadvise() api with the posix semantics, or
distinct functions with descriptive names?


 
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Discussion subject changed to "libuv issue ignored & closed (was: libuv - posix_fadvise() on windows)" by Liam
Liam  
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 More options Nov 29 2011, 5:29 pm
From: Liam <networkimp...@gmail.com>
Date: Tue, 29 Nov 2011 14:29:47 -0800 (PST)
Local: Tues, Nov 29 2011 5:29 pm
Subject: libuv issue ignored & closed (was: libuv - posix_fadvise() on windows)
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I filed a libuv issue for posix_fadvise (which probably should have
been titled "enable omitting pages from filesystem cache on/after
read"), and someone labeled it API & Unix, and then Bert closed it
without comment. I don't get it.

Reading a large collection of files once each (as for backup,
indexing, synchronization) will wipe out the filesystem cache,
impacting performance. I'd think that libuv needs to handle this.

Even if I made my own binding for posix_fadvise() it's not obvious how
to integrate that into a createReadStream(file) object.

On Nov 27, 2:30 pm, Liam <networkimp...@gmail.com> wrote:


 
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Bert Belder  
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 More options Nov 30 2011, 5:15 am
From: Bert Belder <bertbel...@gmail.com>
Date: Wed, 30 Nov 2011 02:15:37 -0800 (PST)
Local: Wed, Nov 30 2011 5:15 am
Subject: Re: libuv issue ignored & closed (was: libuv - posix_fadvise() on windows)
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On Nov 29, 11:29 pm, Liam <networkimp...@gmail.com> wrote:

> I filed a libuv issue for posix_fadvise (which probably should have
> been titled "enable omitting pages from filesystem cache on/after
> read"), and someone labeled it API & Unix, and then Bert closed it
> without comment. I don't get it.

Wut - sorry, I didn't mean to close it (which does not mean that I am
now enthusiastic about the feature.).

 
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Liam  
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 More options Nov 30 2011, 8:31 am
From: Liam <networkimp...@gmail.com>
Date: Wed, 30 Nov 2011 05:31:54 -0800 (PST)
Local: Wed, Nov 30 2011 8:31 am
Subject: Re: libuv issue ignored & closed (was: libuv - posix_fadvise() on windows)
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On Nov 30, 2:15 am, Bert Belder <bertbel...@gmail.com> wrote:

> On Nov 29, 11:29 pm, Liam <networkimp...@gmail.com> wrote:

> > I filed a libuv issue for posix_fadvise (which probably should have
> > been titled "enable omitting pages from filesystem cache on/after
> > read"), and someone labeled it API & Unix, and then Bert closed it
> > without comment. I don't get it.

> Wut - sorry, I didn't mean to close it (which does not mean that I am
> now enthusiastic about the feature.).

Thanks. I renamed the issue. Insights on how to do this in Windows?

 
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Bert Belder  
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 More options Nov 30 2011, 7:11 pm
From: Bert Belder <bertbel...@gmail.com>
Date: Wed, 30 Nov 2011 16:11:02 -0800 (PST)
Local: Wed, Nov 30 2011 7:11 pm
Subject: Re: libuv issue ignored & closed (was: libuv - posix_fadvise() on windows)
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On Nov 30, 2:31 pm, Liam <networkimp...@gmail.com> wrote:

> On Nov 30, 2:15 am, Bert Belder <bertbel...@gmail.com> wrote:

> > On Nov 29, 11:29 pm, Liam <networkimp...@gmail.com> wrote:

> > > I filed a libuv issue for posix_fadvise (which probably should have
> > > been titled "enable omitting pages from filesystem cache on/after
> > > read"), and someone labeled it API & Unix, and then Bert closed it
> > > without comment. I don't get it.

> > Wut - sorry, I didn't mean to close it (which does not mean that I am
> > now enthusiastic about the feature.).

> Thanks. I renamed the issue. Insights on how to do this in Windows?

There is no equivalent of fadvise() on windows.

A flag FILE_FLAG_NO_BUFFERING exists that is specified when opening
the file, similar to O_DIRECT on linux. But it adds constraints when
issuing a read call; you now have to read a multiple of 512 bytes and
your buffers need to be page-aligned.

You can also specify FILE_FLAG_SEQUENTIAL_SCAN which tells windows
that you want to read sequentially. It's probably closer to what you
need.


 
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Liam  
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 More options Nov 30 2011, 9:12 pm
From: Liam <networkimp...@gmail.com>
Date: Wed, 30 Nov 2011 18:12:14 -0800 (PST)
Local: Wed, Nov 30 2011 9:12 pm
Subject: Re: libuv issue ignored & closed (was: libuv - posix_fadvise() on windows)
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On Nov 30, 4:11 pm, Bert Belder <bertbel...@gmail.com> wrote:

> You can also specify FILE_FLAG_SEQUENTIAL_SCAN which tells windows
> that you want to read sequentially. It's probably closer to what you
> need.

It's too bad Node doesn't have a file abstraction; that'd make
accommodating this difference easy.

How about offering both an O_SEQENTIAL flag for fs.open() (a noop on
Unix) and an fs.fadvise() function (a noop on Windows)?


 
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