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Re: DB Block Size in Linux

From: Noons <wizofoz2k_at_yahoo.com.au>
Date: 13 Jan 2004 23:25:15 -0800
Message-ID: <73e20c6c.0401132325.2074a207@posting.google.com>


toby_brown_at_optusnet.com.au (Toby Brown) wrote in message news:<2a84f50c.0401121622.6ccd9a4a_at_posting.google.com>...
> I gather that I can choose the filesystem block size (perhaps during
> Linux installation). So I assume when I'm installing RehHat Linux 8
> and selecting the ext2 filesystem to be the filesystem for that Linux
> installation, I would be able to choose a filesystem block size (I'd
> probably go 4k).

Actually, you can choose the filesystem block size ANYTIME you create a new file system, not just during installation. In fact that would be the best option: create a file system of default block size to keep all your Linux-related software at install time, THEN create additional ones to keep the Oracle data, which you will optimize for Oracle db block size. Not all the Linux install routines will allow you the flexibility of specifying the f/s block size.

> Then creating an Oracle9i database with a db block size larger than 4k
> (e.g. 8k) shouldn't be a problem since the filesystem buffer cache
> would cache a multiple of the filesystem blocks, in this case, a
> multiple of 4k blocks, meaning that an 8k database block size wouldn't
> induce any additional IO (behind the scenes) as I had feared before.

I think so too. The important bit is to use a db block size that is an exact match to the f/s block size or an exact 2-multiple (a multiple of twice its size).
Never, never, a sub-multiple. Unless you plan on doing only FTS.

The other thing like I said, is to make absolutely sure you are creating your database datafiles in an otherwise freshly made and empty file system. It is surprising how many problems can be caused by f/s space management issues, hidden inside the f/s management software itself. Start with a brand new f/s and you have eliminated the vast majority of those.  

> I'm a novice with Oracle+Linux so I hope I haven't over simplified
> this issue above.

Not a worry. I'm no expert either, although Linux is not that far from Unix and that I do know.

Cheers
Nuno Souto
wizofoz2k_at_yahoo.com.au.nospam Received on Wed Jan 14 2004 - 01:25:15 CST

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