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Re: Can a segment span more than one datafiles

From: Paul Brewer <paul_at_paul.brewers.org.uk>
Date: Thu, 15 May 2003 23:00:45 +0100
Message-ID: <3ec4117a_3@mk-nntp-1.news.uk.worldonline.com>


"Peter" <peter_at_nomorenewsspammin.ca> wrote in message news:cff6cvkedqaugm85sugg6mag2v47dv08rv_at_4ax.com...
> A tablespace can span more than one datafiles, but can a segment span
> more than one datafiles? I am just wondering what is the smallest
> Oracle unit that can span different datafiles.
> How about data block spanning datafiles? How about an extent?
>

We need to separate the physical from the logical here, I think.

A tablespace is a logical entity which consists of one or more datafiles. A datafile is just a file in the file system (raw devices excluded here). A segment is also a logical entity (for example a table or an index) which physically consists of one or more extents. The various extents may exist in different datafiles, but each extent will reside in a single datafile.

An extent is a collection of contiguous blocks in a datafile. The block is the lowest physical unit as far as Oracle is concerned.

Does this help?

Regards,
Paul Received on Thu May 15 2003 - 17:00:45 CDT

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