Re: 64-bit queryId?

On Tue, Oct 3, 2017 at 5:55 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:

> On Mon, Oct 2, 2017 at 8:07 PM, Alexander Korotkov
> <a(dot)korotkov(at)postgrespro(dot)ru> wrote:
> > +1,
> > I see 3 options there:
> > 1) Drop high-order bit, as you proposed.
> > 2) Allow negative queryIds.
> > 3) Implement unsigned 64-type.
> >
> > #1 causes minor loss of precision which looks rather insignificant in
> given
> > context.
> > #2 might be rather unexpected for users whose previously had non-negative
> > queryIds. Changing queryId from 32-bit to 64-bit itself might require
> some
> > adoption from monitoring software. But queryIds are user-visible, and
> > negative queryIds would look rather nonlogical.
> > #3 would be attaching hard and long-term problem by insufficient reason.
> > Thus, #1 looks like most harmless solution.
>
> I think we should just allow negative queryIds. I mean, the hash
> functions have behaved that way for a long time:
>
> rhaas=# select hashtext('');
> hashtext
> -------------
> -1477818771
> (1 row)
>
> It seems silly to me to throw away a perfectly good bit from the hash
> value just because of some risk of minor user confusion. I do like
> Michael's suggestion of outputing hexa-like text, but changing the
> types of the user-visible output columns seems like a job for another
> patch. Similarly, if we were to adopt Andres's suggestions of a new
> type or using numeric or Alexander's suggestion of implementing a
> 64-bit unsigned type, I think it should be a separate patch from this
> one.
>
> I would note that such a patch will actually create real
> incompatibility -- extension upgrades might fail if there are
> dependent views, for example -- whereas merely having query IDs start
> to sometimes be negative only creates an incompatibility for people
> who assumed that the int64 type wouldn't actually use its full range
> of allowable values. I don't deny that someone may have done that, of
> course, but I wouldn't guess that it's a common thing... maybe I'm
> wrong.
>

BTW, you didn't comment Tom's suggestion about dropping high-order bit
which trades minor user user confusion to minor loss of precision.
TBH, for me it's not so important whether we allow negative queryIds or
drop high-order bit. I would be anyway very good to have 64-(or 63-)bit
queryIds committed.

------
Alexander Korotkov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company