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Why there is a Limitations on Index size (900...
Why there is a Limitations on Index size (900 Bytes)?
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SQL*
SQL*
Posted Wednesday, August 01, 2012 3:46 AM
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Hi,
Is it correct that all the pages, index/data/iam..etc pages does have the 8KB in size? if yes, why we have this limitation. if not what is the size of the each and every page by tyep. i.e., what is the size of the Index page? What is the max size of the Data Page?
Thank you,
Post #1338394
GilaMonster
GilaMonster
Posted Wednesday, August 01, 2012 3:49 AM
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Yes, all pages are 8kb in size.
Limitation probably to keep the size of the index tree down. Wouldn't make any sense to have 8kb index key, the index tree would be incredibly deep and very inefficient.
Gail Shaw
Microsoft Certified Master: SQL Server 2008, MVP
SQL In The Wild
: Discussions on DB performance with occasional diversions into recoverability
We walk in the dark places no others will enter
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Post #1338397
SQL*
SQL*
Posted Wednesday, August 01, 2012 5:14 AM
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GilaMonster (8/1/2012)
Yes, all pages are 8kb in size.
Limitation probably to keep the size of the index tree down. Wouldn't make any sense to have 8kb index key, the index tree would be incredibly deep and very inefficient.
What about the remaining free space? Around 7 Kb of space will be empty or will it contain any information?
Is the statement is correct that you have provided?
Thanks,
Post #1338425
Lowell
Lowell
Posted Wednesday, August 01, 2012 5:47 AM
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it's not a one to one relationship. more than one index value will be able to fit in each 8k page;
so an index will be made up of as many pages it needs to hold all it's data.
i think you were thinking each index key goes on it's own page, and that's not how the space would be used.
Lowell
--
There is no spoon, and there's no default ORDER BY in sql server either.
Actually, Common Sense is so rare, it should be considered a Superpower. --my son
Post #1338440
GilaMonster
GilaMonster
Posted Wednesday, August 01, 2012 7:31 AM
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SQL* (8/1/2012)
GilaMonster (8/1/2012)
Yes, all pages are 8kb in size.
Limitation probably to keep the size of the index tree down. Wouldn't make any sense to have 8kb index key, the index tree would be incredibly deep and very inefficient.
What about the remaining free space? Around 7 Kb of space will be empty or will it contain any information?
What happens to a data page when you create a row of only 900 bytes? Same thing with an index page.
SQL doesn't put one row per page, it fills the page with as many rows as possible. In the case of 900 byte rows, fitting 9 rows to the page.
I think you may want to revise basic index architecture.
http://www.sqlservercentral.com/articles/Indexing/68439/
http://www.sqlservercentral.com/articles/Indexing/68563/
http://www.sqlservercentral.com/articles/Indexing/68636/
Is the statement is correct that you have provided?
Err... yes.
Gail Shaw
Microsoft Certified Master: SQL Server 2008, MVP
SQL In The Wild
: Discussions on DB performance with occasional diversions into recoverability
We walk in the dark places no others will enter
We stand on the bridge and no one may pass
Post #1338517
SQL*
SQL*
Posted Thursday, August 02, 2012 6:35 AM
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Thank you all (GilaMonster), for your answers.
Post #1339096
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