Re: On-disk bitmap index patch

Tom,

On 7/26/06 7:26 AM, "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> I wonder
> whether they oughtn't use 16-bit instead of 8-bit HRL_WORDs

We tried variations from 8-bit to 32-bit and came to the conclusion that
8-bit was a better match for the more general case. For the moment I forget
exactly why (maybe Jie or Ayush will recall). It's a #define I believe, so
you can play with it to find out.

There's a lot more to be done with this - I think we've got some big gains
ahead.

BTW - lots of excitement here at OSCON about bitmap index, and there's a
fellow who is using the current Bizgres version, but wants *higher*
cardinality support, so I discussed Jie's thoughts about implementing
binning on values, basically combining bit vectors into value bins as the
cardinality increases.

I am still puzzled why our index creation time increases so dramatically as
we approach cardinality 10,000. I know that we found that index page
traversal for append began to take a lot of time as we started to increase
the number of bitvector pages - we had talked about aggregating the append
operations into groups before they were implemented to sequentialize the
access.

- Luke