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maximum number of extents in per undo segment [message #232289] Fri, 20 April 2007 01:20 Go to next message
Dipali Vithalani
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hi friends,
from one book, i read that
"For an undo tablespace with a block size of 8KB, the default maximum number of extents per undo segment is 32765"
I want to know, this calculation is done on which basis?
Please let me know, if anyone know it...

Thanks..

Regards..
Re: maximum number of extents in per undo segment [message #232292 is a reply to message #232289] Fri, 20 April 2007 01:23 Go to previous messageGo to next message
Michel Cadot
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What do you read that?
2*1024*1024*1024 extents for the whole undo tablespace, no limit per undo segment.

Regards
Michel
Re: maximum number of extents in per undo segment [message #232296 is a reply to message #232292] Fri, 20 April 2007 01:28 Go to previous messageGo to next message
Dipali Vithalani
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"What do you read that?"
I think you mean to ask, "where do you read that?"
Right?
Re: maximum number of extents in per undo segment [message #232298 is a reply to message #232296] Fri, 20 April 2007 01:30 Go to previous messageGo to next message
Michel Cadot
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Right! sorry for the wrong word.

Regards
Michel
Re: maximum number of extents in per undo segment [message #232312 is a reply to message #232298] Fri, 20 April 2007 02:07 Go to previous messageGo to next message
Dipali Vithalani
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Book : Sybex - Oca 10g administration I study guide Izo.042
Page no : 405
line no : 9th..
lines are like : Each segment must have a minimum of two extents; the maximum number of extents in an undo segment is high: for an undo tablespace with a block size of 8KB, the default maximum number of extents per undo segment is 32,765.
Re: maximum number of extents in per undo segment [message #232316 is a reply to message #232312] Fri, 20 April 2007 02:19 Go to previous messageGo to next message
Michel Cadot
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After verification this seems correct but there is no mention of that in documentation.
Even if you have no limit on tablespace (that is a limit of 2G), Oracle seems to create its undo segments with a limit of 32765 extents (for 8K blocks, didn't check for others).

Thanks
Michel
Re: maximum number of extents in per undo segment [message #232319 is a reply to message #232316] Fri, 20 April 2007 02:25 Go to previous messageGo to next message
Dipali Vithalani
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Registered: March 2007
Location: India
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After verification this seems correct but there is no mention of that in documentation.

Sorry sir, i can understand only this line from last reply...
Does it mean that, no limit on number of extents in undo segment?
I also read that, even if we specify "unlimited" , maximum 2 billion extents can be allocated to a segment.
Is this correct?
If yes, is it applied on Undo segment?
Re: maximum number of extents in per undo segment [message #232323 is a reply to message #232319] Fri, 20 April 2007 02:37 Go to previous messageGo to next message
Michel Cadot
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It seems correct that 32765 is the limit of number of extents for an undo segment.
I checked for other block size. The limit is alsways 32765.

Theorically, 2 billion is the limit in a LMT but it seems Oracle chooses to make an exception for undo segments.

Regards
Michel
Re: maximum number of extents in per undo segment [message #232325 is a reply to message #232323] Fri, 20 April 2007 02:52 Go to previous messageGo to next message
Dipali Vithalani
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Registered: March 2007
Location: India
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So, as a conclusion, i can note that
- maximum limit for extents in undo segment is 32765 ( for block size is 8kb),
- and for other type of segments, conceptually, 2 billion.
am i right?

And the question was, how the oracle calculats that for 8kb block size, it can allocate maximum 32765 extents... On which basis, this maximum size is decided..

Thanks..

Regards..
Re: maximum number of extents in per undo segment [message #232329 is a reply to message #232325] Fri, 20 April 2007 03:05 Go to previous messageGo to next message
Michel Cadot
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The limit is 32765 extents per undo segment for any block size as per my tests (no documentation in technet nor metalink).

I feel that limit is "small int" but can't really say.

Regards
Michel

Re: maximum number of extents in per undo segment [message #232335 is a reply to message #232329] Fri, 20 April 2007 03:33 Go to previous message
Dipali Vithalani
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Registered: March 2007
Location: India
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I can relay on your test sir.
Thanks for the help
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