[Bizgres-general] A bitmap index access method is available in bizgres CVS tip

[Sam Vilain]

On Mon, 2005-12-19 at 21:25 +1300, Mark Kirkwood wrote:
> 10 value bitmap for 10000000 rows requires 10*10000000/8 = 12500000 (~12Mb).
> 
> This is quite small (whereas the 10 value bitmap indexes are ~150Mb).
> 
> To actually use the bitmap you need a map between the bitmap "array" 
> position and blocknumber,itemid (or similar) of the heap relation. I am 
> guessing that is what your "bm_internal_t*" guys do(?).  Is this where 
> the extra space is being used? (the on-disk bm_* are very small, so I 
> guess it is not).

On Oracle at least, this mapping is only necessary if you are using an
"index organised table" (I *think* this maps cleanly to the concept of a
primary unique key in Pg?).

Otherwise it's just one bit, one row... and that's before adding the
compression.

Sam.