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why does oracle need EXTENTS? [message #226615]

Sun, 25 March 2007 22:25

kssarayu
Messages: 18
Registered: March 2007

Junior Member

hi,
I want to know why oracle really has a concept called EXTENTS
I know that
---> Block is the lowest storage unit
---> EXTENT Is collection of contiguous Blocks
---> SEGMENT has EXTENTS
---> TABLESPACE will consists different SEGMENTS

My doubt is, what is the real need of EXTENTS? Why can't we talk directly in number of blocks for segments instead of extents?

Was EXTENT used because it represents contiguous blocks or is there any other reason.

Thanks in advance.

Regards,
Sarayu K.S.

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Re: why does oracle need EXTENTS? [message #226616 is a reply to message #226615]

Sun, 25 March 2007 22:34

BlackSwan
Messages: 26766
Registered: January 2009
Location: SoCal

Senior Member

Why post question here & possible get incorrect response(s) when you can simply read the fine manuals found at http://tahiti.oracle.com & get authoritative answers?
http://download-west.oracle.com/docs/cd/B19306_01/server.102/b14220/logical.htm#sthref297

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Re: why does oracle need EXTENTS? [message #226617 is a reply to message #226615]

Sun, 25 March 2007 22:42

nmacdannald
Messages: 460
Registered: July 2005
Location: Stockton, California - US...

Senior Member

When a tablespace fills up it allocates another extent. The extent must be a contiguous number of disk blocks.
Oracle wants to talk to the data and having extents lets it do that regardless of the o/s block size or o/s type. Same thing with tablespaces. Think kernel and schell.

There are usually two reasons Oracle does things in a certain way:
1) To make the db correct.
2) To make the db fast.

[Updated on: Sun, 25 March 2007 22:47]

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Re: why does oracle need EXTENTS? [message #226618 is a reply to message #226615]

Sun, 25 March 2007 22:46

kssarayu
Messages: 18
Registered: March 2007

Junior Member

Thanks anacedent for your quick reply.

I have two points to mention.

1) For beginners, who read the oracle documentation, we may have some doubts which we want to get clarified. We choose forums like orafaq.com, because we get quick replies from experts in oracle.
Even if someone posts incorrect responses, i strongly beleive there are many experts who can correct them.
2) I did go through the documentation and thats how i gave some information on whatever i know.

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Re: why does oracle need EXTENTS? [message #226619 is a reply to message #226615]

Sun, 25 March 2007 22:48

BlackSwan
Messages: 26766
Registered: January 2009
Location: SoCal

Senior Member

>I did go through the documentation and thats how i gave some information on whatever i know.
Then post the source URL so everyone can benefit from context of statement/question.

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