Subject Blob levels
Author Dmitry Yemanov

Now we have three blob levels (0, 1, 2) which define how the blob is
physically stored. Level 0 means on-page data, level 1 contains pointers to
data pages, level 2 contains pointers to pointers to data pages. Hence a
maximum blob size is somewhere near:

(page_size / 4) * (page_size / 4) * page_size

which means ~64MB for 1K pages and ~4GB for 4K pages.

I don't know whether this restriction is documented somewhere or not. But
the real problem is that the code never checks whether a level 2 blob can be
overfilled. Just try to load a 65MB blob into a 1K page size database and
the engine bugchecks. I've just added an overflow check into v2.0 to report
a better error message instead. But I have a question: do we consider this
limitation okay? Or perhaps we could extend the current scheme to have level
3, 4 etc blobs to address bigger data? Of course, this talk is not about