Hi, I don't think I can't help with code review, but I loaded our largest customer's schema into pg12dev and tested with this patch. It's working well - thanks for your work.
Details follow. We have tooo many tables+indices so this vastly improves planning speed. Our large customers have ~300 parent tables and total ~20k child tables with total ~80k indices. Our largest tables heirarchies have ~1200 child tables, which may have as many as 6-8 indices each. And 5-10 of the largest heirarchies are unioned together in a view. Running pg11.1, explaining query for the largest view with condition eliminates all but today's tables can take several minutes with a cold cache, due to not only stat()ing every file in every table in a partition heirarchy, before pruning, but also actually open()ing all their indices. Running 11dev with your v10 patch applied, this takes 2244ms with empty buffer cache after postmaster restarted on a totally untuned instance (and a new backend, with no cached opened files). I was curious why it took even 2sec, and why it did so many opens() (but not 20k of them that PG11 does): [pryzbyj@database postgresql]$ cut -d'(' -f1 /tmp/strace-12dev-explain |sort |uniq -c |sort -nr 2544 lseek 1263 open ... It turns out 1050 open()s are due to historic data which is no longer being loaded and therefor never converted to relkind=p (but hasn't exceeded the retention interval so not yet DROPped, either). Cheers, Justin