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SQL IO in pages

when SQL requests data, it gets one extent(64k) at a time from Windows. But isn't SQL IOs done in multiple's of 8k pages?

What pattern in SQL Activity determines if the SQL IO comes in 1 or 2 or 3 or 4 or 5 or 6 or 7 or 8 pages, at one time? Is it different for data, log, indexes etc

Thanks
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anushahanna
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anushahanna
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chapmandewCommented:
>> SQL IOs done in multiple's of 8k pages?

No, it is done at the extent level.

>>What pattern in SQL Activity determines if the SQL IO comes in 1 or 2 or 3 or 4 or 5 or 6 or 7 or 8 pages, at one time?

Everything in SQL is done at the extent level.  
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chapmandewCommented:
by the way,and extent is 8-8K pages.  = 64 K
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anushahannaAuthor Commented:
so even if only one or two pages are involved for a read or a write, still an extent will be 'spent' for IO?
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chapmandewCommented:
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chapmandewCommented:
I would also recommend this book if you are super interested with how sql works under the covers...very neat stuff.

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anushahannaAuthor Commented:
correct me if i am wrong:
you  mean to say If it is 8 pages or more then it uses uniform extent for IO and if it is less than 59k of data, then it uses Mixed extent?
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anushahannaAuthor Commented:
thanks for the book reco.
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chapmandewCommented:
I am not sure if 59K is the correct figure, but a table will use mixed extents to the point where it has 8 full pages..then it uses uniform extents.
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