[Bizgres-general] Re: Mapping from bitmap array position to heap location (was : A bitmap index access method is available...)

[Simon Riggs]

On Tue, 2006-01-03 at 11:05 +1300, Mark Kirkwood wrote:
> Jie Zhang wrote:

> > One interesting point is that you choose 2048 as max offset number. Is this
> > true for all cases? If so, we can set the word size to 8-bit to further
> > increase the bitmap compression rate.

> If sizeof(ItemIdData) is always *at least* 4 bytes (which seems 
> reasonable) then the biggest MaxOffsetNumber can be is 32768/4 = 8192 
> (i.e if you choose 32K pages).

We're always pointing to heap blocks, for which the fixed overhead is
always at least another 28 bytes. So the actual maximum with 32K pages
is about 1000, even assuming the table is 1 column, nullable, with null
value. 

Best Regards, Simon Riggs