“According to Konstantin Knizhnik, there are about 2,000 such variables currently used by the PostgreSQL server.”
PostgreSQL spawns one process per client, and Andres Freund says the TLB misses add up once connections pile up. The fix means taming about 2,000 global variables, and Tom Lane calls the whole plan “a disaster” that will ship “more than one security-grade bug”. Knizhnik already built a threaded port, and almost nobody looked at it. Nobody has volunteered to do the work either, so the consensus is about a project with no staff.