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  2. MIDRANGE-L
  3. November 2007

RE: Porting Guide and Statement made about Char Vs VarChar

That link has an interesting comment in it in the "Using LOBs and
VARCHAR in the same table" part:

"When a column stored in the overflow storage area is referenced,
currently all of the columns in that area are paged into memory. ... For
example, A VARCHAR(256) column retrieved by application has side-effect
of paging in two 5 MB BLOB columns that are in the same row."

Ouch! While I'm sure there a good reason for that, I can't imagine what
it is. Since the data is by definition variable in length it's not like
the storage for the variable length and LOB columns are allocated
contiguously, at least I hope they aren't. Therefore what's the point in
paging in all the data? What if the LOB was 50MB, or 500?

I'm now off to confirm that this isn't true on another DBMS where I
regularly use LOBs and VarChar fields in the same row. :)

-Walden


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