linux-ext4 - Re: Htree concept

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Message-ID: <mj019e$f8f$1@ger.gmane.org>
Date:	Wed, 13 May 2015 19:22:54 +0200
From:	"U.Mutlu" <for-gmane@...luit.com>
To:	linux-ext4@...r.kernel.org
Subject: Re: Htree concept

Eric Sandeen wrote on 05/13/2015 06:29 PM:
> On 5/13/15 10:37 AM, U.Mutlu wrote:
>> Hi,
>> I'm writing a toy-fs, and discover a major shortcoming
>> (finding a given child (dir/file) as fast as possible),
>> which other developers (ie. ext3/4) had encountered long ago too.
>> They introduced HTree. The info on HTree on the web is scarce
>> or I couldn't find the right texts/papers yet.
>> I wonder how HTree works on a conceptual basis.
>> Could a kind soul enligten me pls. TIA.
>
> Regarding htree details, did you look at:
>
> http://en.wikipedia.org/wiki/HTree
>
> which points to:
>
> http://ext2.sourceforge.net/2005-ols/paper-html/node3.html
> and more specifically,
> http://web.archive.org/web/20131203105316/http://www.linuxshowcase.org/2001/full_papers/phillips/phillips_html/index.html
>
> ?

Thanks, the wiki page and its refs I knew, but needed some more info.

Ok, it is written that HTree uses 32bit (or 64?) hashes for keys.
I wonder if it wouldn't be better if one instead would use that space
(32/64 bit) for storing the first n chars of the key (ie. of the dir/file name)
and keeping the directory entries in a sorted order on the disk,
and then do a bsearch instead of doing sequential table lookup using HTree?
I wonder what the "Tree"-part of HTree stand for in this context.
Am I right in my assumption that HTree mainly means the hashing mechanism,
but does not use any binary search mechanism for searching the key?

-- 
Thx
Uenal

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