At Mon, 28 Mar 2022 12:17:50 -0400, Robert Haas <robertmh...@gmail.com> wrote in > On Mon, Mar 21, 2022 at 3:02 PM Alvaro Herrera <alvhe...@alvh.no-ip.org> > wrote: > > > 2. Why not instead change the code so that the operation can succeed, > > > by creating the prerequisite parent directories? Do we not have enough > > > information for that? I'm not saying that we definitely should do it > > > that way rather than this way, but I think we do take that approach in > > > some cases. > > > > It seems we can choose freely between these two implementations -- I > > mean I don't see any upsides or downsides to either one. > > What got committed here feels inconsistent to me. Suppose we have a > checkpoint, and then a series of operations that touch a tablespace, > and then a drop database and drop tablespace. If the first operation > happens to be CREATE DATABASE, then this patch is going to fix it by > skipping the operation. However, if the first operation happens to be > almost anything else, the way it's going to reference the dropped > tablespace is via a block reference in a WAL record of a wide variety > of types. That's going to result in a call to > XLogReadBufferForRedoExtended() which will call > XLogReadBufferExtended() which will do smgrcreate(smgr, forknum, true) > which will in turn call TablespaceCreateDbspace() to fill in all the > missing directories.
Right. I thought that recovery avoids that but that's wrong. This behavior creates a bare (non-linked) directly within pg_tblspc. The directory would dissapear soon if recovery proceeds to the consistency point, though. > I don't think that's very good. It would be reasonable to decide that > we're never going to create the missing directories and instead just > remember that they were not found so we can do a cross check. It's > also reasonable to just create the directories on the fly. But doing a > mix of those systems doesn't really seem like the right idea - > particularly because it means that the cross-check system is probably > not very effective at finding actual problems in the code. > > Am I missing something here? No. I agree that mixing them is not good. On the other hand we already doing that by heapam. AFAICS sometimes it avoid creating a new page but sometimes creates it. But I don't mean to use the fact for justifying this patch to do that, or denying to do that. regards. -- Kyotaro Horiguchi NTT Open Source Software Center
