On Fri, Apr 27, 2012 at 1:51 AM, Josh Berkus <josh@agliodbs.com> wrote:
> 1. Out of 700 columns, columns 301+ are all Null, so we map them away.
> 2. User updates column 688 to non-null
> 3. Suddenly we have a MUCH larger row which will no longer fit on the page.
Note that this is only actually 48 bytes more in the null bitmap in
this scenario. That's part of Tom's point that the null bitmap is so
dense that you have to be talking about some pretty huge number of
columns before the size savings are noticeable. Saving 48 bytes is
nothing to sneeze at but it's hardly an impractical update to handle.
--
greg