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

On Mon, Oct 05, 2020 at 11:23:50PM -0400, Bruce Momjian wrote:
> On Tue, Oct  6, 2020 at 11:11:27AM +0800, Julien Rouhaud wrote:
>> Maybe we could add a new hook for only queryid computation, and add a
>> GUC to let people choose between no queryid computed, core computation
>> (current pg_stat_statement) and 3rd party plugin?
> 
> That all seems very complicated.  If we go in that direction, I suggest
> we just give up getting any of this into core.

A GUC would have at least the advantage to make the computation
consistent for any system willing to consume it, with the option to
not pay any potential performance impact, though I have to admit that
just moving the query ID computation of PGSS into core may not be the
best option as a query ID of 0 means the same thing for a utility, for
an initialization, and for a backend running a query with an unknown
value, but that could be worked out.

FWIW, I think that adding the system ID in the hash is too
restrictive, as it could be interesting for users to do stat
comparisons across multiple systems running the same major version.
It would be better to not give any strong guarantee that the query ID
computed will remain consistent across major versions so as it is
possible to keep improving it.  Also, if nothing has been done that
changes the hashing computation, I see little benefit in forcing a
breakage by adding something like PG_MAJORVERSION_NUM or such in the
hash computation.
--
Michael