On Fri, Aug 14, 2009 at 12:37:14PM +, Scara Maccai wrote:
I'm asking because since the page layout includes a null bitmap that
If it is present it begins just after the fixed header and occupies
enough bytes to have one bit per data column, I guess that when all
the bits in the bitmap are used when I add a column (even a nullable
one) the table gets rewritten (to add a new byte to the nullable
bitmap); is this true?
Sort of; there is indeed a null bitmap saying which columns are null.
But there's also a number saying how many columns there are and hence
each row knows if a new column is going to be off the end and means it
doesn't need to rewrite the table when adding a new NULLable column.
I made a suggestion about how to generalize this to non-NULLable columns
with a default value, but haven't written any code to make it do this
yet.
--
Sam http://samason.me.uk/
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