Size of the NULL bitmap

When working out the storage requirements on a per-row basis, how is the size of the NULL bitmap determined?

I know that there are CEILING(n / 8) bytes of NULL bitmap per n columns - but what I don't know is whether there are always two column count bytes or not.

Can anyone confirm / deny?
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asked Apr 21, 2011 at 02:04 AM in Default

Matt Whitfield gravatar image

Matt Whitfield ♦♦
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I'm sure Klaus covered this in his talk at SQLBits... but I can't remember
Apr 21, 2011 at 02:20 AM ThomasRushton ♦
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1 answer: sort voted first

According the MSDN, there are the 2 bytes alwas: Null_Bitmap = 2 + ((Num_Cols + 7) / 8)

Estimating the Size of a Heap

[Estimating the Size of a Clustered Index][2]

[2]: http://msdn.microsoft.com/en-us/library/ms178085.aspx
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answered Apr 21, 2011 at 02:47 AM

Pavel Pawlowski gravatar image

Pavel Pawlowski
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Awesome, cheers - was clearly having an information finding fail day :)
Apr 21, 2011 at 05:12 AM Matt Whitfield ♦♦
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asked: Apr 21, 2011 at 02:04 AM

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Last Updated: Apr 21, 2011 at 02:04 AM