From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mikado Subject: Re: Question regarding to store file system metadata in database Date: Sun, 19 Mar 2006 12:07:42 +0700 Message-ID: <441CE71E.5090503@gmail.com> References: <4ae3c140603182048k55d06d87ufc0b9f0548574090@mail.gmail.com> Reply-To: mikado4vn@gmail.com Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Return-path: Received: from zproxy.gmail.com ([64.233.162.198]:63200 "EHLO zproxy.gmail.com") by vger.kernel.org with ESMTP id S1751392AbWCSFEO (ORCPT ); Sun, 19 Mar 2006 00:04:14 -0500 Received: by zproxy.gmail.com with SMTP id o37so972817nzf for ; Sat, 18 Mar 2006 21:04:13 -0800 (PST) To: Xin Zhao In-Reply-To: <4ae3c140603182048k55d06d87ufc0b9f0548574090@mail.gmail.com> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 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 > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.2.1 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFEHOceNWc9T2Wr2JcRAsKKAJ9t1fRZ1xczAaeruDUqTNeLMcGuiwCfeTNt 31pFUK79Q7BE1AptbmNqr9Q= =LbiF -----END PGP SIGNATURE-----