Re: improve transparency of bitmap-only heap scans

On Fri, Mar 20, 2020 at 7:09 AM James Coleman <jtc331@gmail.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?

2.
+ * unfetched_pages    total number of pages not retrieved due to vm
  * prefetch_iterator  iterator for prefetching ahead of current page
  * prefetch_pages    # pages prefetch iterator is ahead of current
  * prefetch_target    current target prefetch distance
@@ -1591,6 +1592,7 @@ typedef struct BitmapHeapScanState
  Buffer pvmbuffer;
  long exact_pages;
  long lossy_pages;
+ long unfetched_pages;

Can we name it as skipped_pages?

3. Can we add a test or two for this functionality?



-- 
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com