Re: Bitmap index status

On Tue, 19 Sep 2006, Heikki Linnakangas wrote:

> Jie Zhang wrote:
> > Hi Heikki and all,
> >
> > Please find the latest bitmap index patch in the attachment. This patch is
> > generated against the postgresql cvs head.
> >
>
> Thanks.
>
> The handling of stream and hash bitmaps looks pretty complicated to me.
> All the bitmap-related nodes have logic to handle both types slightly
> differently. It all seems to come down to that if a subnode (or
> amgetbitmap in a bitmap index scan node) returns a StreamBitmap, the
> caller needs to call the subnode many times, until it returns a NULL.
> With a HashBitmap, the caller only calls the subnode once.
>
> I think amgetbitmap should be called just once per index scan, and it
> should return either a hash bitmap or a stream bitmap. The same applies
> to all the executor nodes that return bitmaps, they would only return a
> single HashBitmap or StreamBitmap, and the upper node would call
> tbm_iterate repeatedly on that.
>
> StreamBitmap would contain a callback (filled by the indexam) that
> tbm_iterate would call to fill the next TBMIterateResult.

Right, this was the approach taken by an earlier version of the patch I
had worked on. It was significantly uglified by the need to keep the index
state around and to be careful about what amrescan might do behind out
back. I will, however, introduce the idea again because it makes the code
much cleaner and more logical, as you seem to suggest.

Thanks,

Gavin