Re: improve transparency of bitmap-only heap scans

> Looking at the discussion where the feature was added, I think changing the
> EXPLAIN just wasn't considered.

I think this is an oversight. It is very useful to have this on
EXPLAIN.

> The attached patch adds "avoided" to "exact" and "lossy" as a category
> under "Heap Blocks".

It took me a while to figure out what those names mean. "unfetched",
as you call it on the code, may be more descriptive than "avoided" for
the new label. However I think the other two are more confusing. It
may be a good idea to change them together with this.

> I think the name of the node should also be changed to "Bitmap Only Heap
> Scan", but I didn't implement that as adding another NodeTag looks like a
> lot of tedious error prone work to do before getting feedback on whether
> the change is desirable in the first place, or the correct approach.

I am not sure about this part. In my opinion it may have been easier
to explain to users if "Index Only Scan" had not been separate but
"Index Scan" optimization.