Re: Feature improvement: can we add queryId for pg_catalog.pg_stat_activity view?

On Mon, Oct  5, 2020 at 07:58:42PM -0300, Álvaro Herrera wrote:
> On 2020-Oct-05, Tom Lane wrote:
> 
> > FWIW, I think this proposal is a mess.  I was willing to hold my nose
> > and have a queryId field in the internal Query struct without any solid
> > consensus about what its semantics are and which extensions get to use it.
> > Exposing it to end users seems like a bridge too far, though.  In
> > particular, I'm afraid that that will cause people to expect it to have
> > consistent values across PG versions, or even just across architectures
> > within one version.
> 
> I wonder if it would help to purposefully change the computation so that
> it is not -- for instance, hash the system_identifier as initial value.
> Then users would be forced to accept that it'll change as soon as it
> migrates to another server or is upgraded to a new major version.

That seems like a good idea, but it would prevent cross-cluster
same-major-version comparisons, which seems like a negative.  Perhaps we
should add the major version into the hash to handle this.  Ideally,
let's just put a queryid-hash-version into to the hash, so if we change
the computation, we just update the hash version and nothing matches
anymore.

I do think the queryid has to display independent of pg_stat_statements,
because I can see people using queryid for log file and pg_stat_activity
comparisons.  I also think the ability to have queryid accessible is an
important feature outside of pg_stat_statements, so I do think we need a
way to move this idea forward.

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EnterpriseDB                             https://enterprisedb.com

  The usefulness of a cup is in its emptiness, Bruce Lee