Hi, To me it seems like a noticable layering violation for dbsize.c to directly stat() files in the filesystem, without going through smgr.c. And now tableam.
This means there's code knowing about file segments outside of md.c - which imo shouldn't be the case. We also stat a lot more than necessary, if the relation is already open - when going through smgr.c we'd only need to stat the last segment, rather than all previous segments. Always going through smgr would have the disadvantage that we'd probably need a small bit of logic to close the relation's smgr references if it previously wasn't open, to avoid increasing memory usage unnecessarily. dbsize.c directly stat()ing files, also means that if somebody were to write a tableam that doesn't store data in postgres compatible segmented files, the size can't be displayed. I think we should change dbsize.c to call RelationGetNumberOfBlocksInFork() for relkinds != TABLE/TOAST/MATVIEW, and a new AM callback for those. Probably with the aforementioned additional logic of closing smgr references if they weren't open before the size computation. Imo this pretty clearly is v13 work. I'd assume that pg_database_size*() would continue the same way it does right now. Greetings, Andres Freund
