Re: explain analyze rows=%.0f

On Wed, Feb 12, 2025 at 5:10 AM Ilia Evdokimov
<ilya(dot)evdokimov(at)tantorlabs(dot)com> wrote:
> I think the idea of keeping two significant digits after the decimal
> point is quite reasonable. The thing is, rows=0.000001 or something
> similar can only occur when loops is quite large. If we show the order
> of magnitude in rows, it will be easier for the user to estimate the
> order of total rows. For example, if we see this:
>
> rows=0.000056 loops=4718040
>
> the user can quickler approximate the order of total rows for analyzing
> the upper levels of the query.

I agree that showing 2 digits after the decimal point in all cases is
not ideal, but I suggest that we take a practical approach. Figuring
out dynamically what number of decimal digits to display in each case
sounds complicated and we may spend a bunch of time arguing about the
details of that and get nothing committed. If we just show 2 digits
after the decimal point, it will not be perfect, but it will be 10^2
times better than what we have now.

If I'm honest, what I actually think we should do is stop dividing
values by nloops before printing them out. Every time I'm looking at a
quantity that has been divided by nloops, the very first thing I do is
try to figure out what the original value was. The whole reason I want
to display at least a couple of decimal digits here is so that I can
do that more accurately, but of course the dream would be not having
to reverse engineer it like that at all. However, I expect fierce
opposition to that idea, and no matter how misguided I may think that
opposition might be, a patch in the tree is worth two in the
CommitFest.

--
Robert Haas
EDB: http://www.enterprisedb.com