On Tue, Oct 18, 2022 at 12:59 PM Tom Lane <t...@sss.pgh.pa.us> wrote: > There is no text suggesting that it's okay to miss, or to double-return, > an entry that is present throughout the scan. So I'd interpret the case > you're worried about as "forbidden by POSIX". Of course, it's known that > NFS fails to provide POSIX semantics in all cases --- but I don't know > if this is one of them.
Yeah, me neither. One problem I see is that, even if the behavior is forbidden by POSIX, if it happens in practice on systems people actually use, then it's an issue. We even have documentation saying that it's OK to use NFS, and a lot of people do -- which IMHO is unfortunate, but it's also not clear what the realistic alternatives are. It's pretty hard to tell people in 2022 that they are only allowed to use PostgreSQL with local storage. But to put my cards on the table, it's not so much that I am worried about this problem myself as that I want to know whether we're going to do anything about it as a project, and if so, what, because it intersects a patch that I'm working on. So if we want to readdir() in one fell swoop and cache the results, I'm going to go write a patch for that. If we don't, then I'd like to know whether (a) we think that would be theoretically acceptable but not justified by the evidence presently available or (b) would be unacceptable due to (b1) the potential for increased memory usage or (b2) some other reason. -- Robert Haas EDB: http://www.enterprisedb.com
