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Message-ID: <4ae3c140603190948s4fcd135er370a15003a0143a8@mail.gmail.com>
Date: Sun, 19 Mar 2006 12:48:07 -0500
From: "Xin Zhao" <uszhaoxin@gmail.com>
To: mikado4vn@gmail.com
Subject: Re: Question regarding to store file system metadata in database
Cc: linux-kernel <linux-kernel@vger.kernel.org>, linux-fsdevel@vger.kernel.org
In-Reply-To: <441CE71E.5090503@gmail.com>
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well, the database could reside on another file system. So the
database based file system could be a secondary file system but
provide more features and  better performance. I am not saying that
database-based file system must be the only filesystem on the system.

On 3/19/06, Mikado <mikado4vn@gmail.com> wrote:
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> Where is that database located, on other filesystem or on database-based
> filesystem?
>
> Xin Zhao wrote:
> > I was wondering why only few file system uses database to store file
> > system metadata. Here, metadata primarily refers to directory entries.
> > For example, one can setup a database to store file pathname, its
> > inode number, and some extended attribution. File pathname can be used
> > as primary key. As such, we can achieve pathname to inode mapping as
> > well as many other features such as fast search and extended file
> > attribute management. In contrast, storing file system entries in
> > directory files may result in slow dentry search. I guess that's why
> > ReiserFS and some other file systems proposed to use B+ tree like
> > strucutre to manage file entries. But why not simple use database to
> > provide the same feature? DB has been heavily optimized to provide
> > fast search and should be good at managing metadata.
> >
> >  I guess one concern about this idea is  performance impact caused by
> > database system. I ran a test on a mysql database: I inserted about
> > 1.2 million such kind of records into an initially empty mysql
> > database. Average insertion rate is about 300 entries per second,
> > which is fast enough to handle normal file system burden, I think.  I
> > haven't try the query speed, but I believe it should be fast enough
> > too (maybe I am wrong, if so, please point that out.).
> >
> > Then I am a little curious why only few people use database to store
> > file system metadata, although I know WinFS plans to use database to
> > manage metadata. I guess one reason is that it is difficult for kernel
> > based file system driver to access database. But this could be
> > addressed by using efficient kernel/user communication mechanism.
> > Another reason could be the worry about database system. If database
> > system crashes, file system will stop functioning too. However, the
> > feature needed by file system is really a small part of database
> > system, A reduced database system should be sufficient to provide this
> > feature and be stable enough to support a file system.
> >
> > Can someone point out more issues that could become obstables to using
> > database to manage metadata for a file system?
> >
> > Many thanks!
> > Xin
> > -
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