> > but the opposite may be > > not necessarily true: a query ID could be associated with multiple > > plan patterns (aka multiple plan IDs). What this offers is that we > > know about which plan one query is currently using in live, for a > > given query ID. > Okay, as I've said before, it seems practical. I just worry because I > see that people don't understand that queryId is a more or less > arbitrary value that may or may not group queries that differ only by > constants to a single "Query Class". I think the same attitude will be > paid to planId. It is okay for statistics. However, non-statistical > extensions need more guarantees and want to put different logic into > these values. > For now, we have examples of only statistical extensions in open-source > and may live with a proposed solution.
statistical/monitoring reasons are an important use case. Detecting plan changes, load attributed to a specific plan, etc. However, I also do see other extensions that could implement a plan_id that has meaning beyond statistical/monitoring purposes. Plan management/enforcement is another use-case. > >> So, it seems that extensions may conflict with the same field. Are we sure > >> that will happen if they are loaded in different orders in neighbouring > >> backends? > > > > Depends on what kind of computation once wants to do, and surely > > without some coordination across the extensions you are using these > > cannot be shared, but it's no different from the concept of a query > > ID. > Hmm, queryId generation code lies in the core and we already came to > terms that this field has only a statistical purpose. Do you want to > commit planId generation code? But, extensions don't necessarily need to rely on the core queryId. They can generate their own queryId. We have it documented for compute_query_id as such [0] "Note that an external module can alternatively be used if the in-core query identifier computation method is not acceptable" [0] https://www.postgresql.org/docs/current/runtime-config-statistics.html#GUC-COMPUTE-QUERY-ID -- Sami Imseih Amazon Web Services (AWS)
