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Concept of Data and Index pages


Concept of Data and Index pages

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sql crazy kid
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Data pages stores data other than text,varchar(max),Image..etc .
Index page stores index entries.

If i created a clustered index ,that physically sorted as the actual data available on the leaf node.
When i query data based on my clustered key,does this get data from index page,or from the data page?
If this from Index page, same data stored in data page as well?

Please help me to understand the concept of Data and Index Pages.;-)

GilaMonster
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The leaf level of the clustered index are data pages (and are not necessarily stored in physical order). The non-leaf levels of the clustered index are index pages. Leaf and non-leaf levels of nonclustered indexes are index pages


Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

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sql crazy kid
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Really helpful... Thanks
sql crazy kid
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Clustered index always seen sorted table in physical order, As per the previous this is not necessarily stored in physical order,Is there any specific case clustered index not sorted in physical order?

"The leaf level of the clustered index are data pages (and are not necessarily stored in physical order)."

Thanks in advance
GilaMonster
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sql crazy kid (12/27/2013)
Is there any specific case clustered index not sorted in physical order?


No specific case. It's the norm in fact.

Don't mistake query results order (which results from logical storage order and query processor behaviour) with physical storage order.


Gail Shaw
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LutzM
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I recently came across an index defintion I thought to be inefficient:


CREATE TABLE myTable (myId INT IDENTITY(1,1))
CREATE CLUSTERED INDEX weird_index ON myTable(myId DESC)



The reson for being inefficient from my point of view:
The values of myId are increasing but the sort order of the clustered index is descending.
Wouldn't this lead to a high frequence of page splits since the next identity value would be physically stored "before" the previous value?

Or am I missing something here?



Lutz
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sql crazy kid
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Kindly give some more ideas about Internal architecture of Non Leaf nodes.
As per my understanding this having page header,index rows[key and pointer] which helps to find next Non Leaf node/Leaf node.
Correct me if i am wrong .
How this finding works with page header and index rows[key and pointer].
GilaMonster
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http://www.sqlservercentral.com/articles/Indexing/68439/
http://www.sqlservercentral.com/articles/Indexing/68563/
http://www.sqlservercentral.com/articles/Indexing/68636/


Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
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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Jeff Moden
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As well as the marvelous articles that Gail posted, Books Online has some great information in it (if you don't know what Books Online is, post back... you cannot live without it) under an index search of "index architecture [SQL Server]".

--Jeff Moden

RBAR is pronounced ree-bar and is a Modenism for Row-By-Agonizing-Row.
First step towards the paradigm shift of writing Set Based code:
Stop thinking about what you want to do to a row... think, instead, of what you want to do to a column.
Although they tell us that they want it real bad, our primary goal is to ensure that we dont actually give it to them that way.
Although change is inevitable, change for the better is not.
Just because you can do something in PowerShell, doesnt mean you should. Wink

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sql crazy kid
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Jeff Moden (12/29/2013)
As well as the marvelous articles that Gail posted, Books Online has some great information in it (if you don't know what Books Online is, post back... you cannot live without it) under an index search of "index architecture [SQL Server]".


Hello Jeff,
Kindly post the link of Books Online . That would be additional for me to which Gail has posted ,
Go


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