Re: improve transparency of bitmap-only heap scans

On Tue, Mar 24, 2020 at 10:54:05AM +0530, Amit Kapila wrote:
> On Fri, Mar 20, 2020 at 7:09 AM James Coleman <jtc331(at)gmail(dot)com> wrote:
> >
> > Awesome, thanks for confirming with an actual plan.
> >
> > > I don't think it matters in nontext mode, but at least in text mode, I think
> > > maybe the Unfetched blocks should be output after the exact and lossy blocks,
> > > in case someone is parsing it, and because bitmap-only is a relatively new
> > > feature. Its output is probably less common than exact/lossy.
> >
> > I tweaked that (and a comment that didn't reference the change); see attached.
> >
>
> Few comments:
> 1.
> -
> - if (tbmres->ntuples >= 0)
> + else if (tbmres->ntuples >= 0)
> node->exact_pages++;
>
> How is this change related to this patch?

Previously, a page was either "exact" or "lossy".
Now it's one of exact/lossy/skipped.
(But not exact/lossy but in either case might be skipped).

if (skip_fetch)
{
/* can't be lossy in the skip_fetch case */
Assert(tbmres->ntuples >= 0);

/*
* The number of tuples on this page is put into
* node->return_empty_tuples.
*/
node->return_empty_tuples = tbmres->ntuples;
+ node->unfetched_pages++;
}
else if (!table_scan_bitmap_next_block(scan, tbmres))
{
/* AM doesn't think this block is valid, skip */
continue;
}
-
- if (tbmres->ntuples >= 0)
+ else if (tbmres->ntuples >= 0)
node->exact_pages++;
else
node->lossy_pages++;

--
Justin