Peter Eisentraut <peter.eisentr...@enterprisedb.com> wrote: > On 04.07.22 18:35, Antonin Houska wrote: > >> Attached is a new version of the patch, to evaluate what the API use in the > >> backend could look like. I haven't touched places where the file is > >> accessed > >> in a non-trivial way, e.g. lseek() / fseek() or pg_pwrite() / pg_pread() is > >> called. > > Rebased patch set is attached here, which applies to the current master. > > (A few more opportunities for the new API implemented here.) > > I don't understand what this patch set is supposed to do. AFAICT, the thread > originally forked off from a TDE discussion and, considering the thread > subject, was possibly once an attempt to refactor temporary file access to > make integrating encryption easier? The discussion then talked about things > like saving on system calls and excising all OS-level file access API use, > which I found confusing, and the thread then just became a general TDE-related > mini-discussion.
Yes, it's an attempt to make the encryption less invasive, but there are a few other objectives, at least: 1) to make the read / write operations "less low-level" (there are common things like error handling which are often just copy & pasted from other places), 2) to have buffered I/O with configurable buffer size (the current patch version still has fixed buffer size though) It's true that the discussion ends up to be encryption-specific, however the scope of the patch is broader. The first meassage of the thread references a related discussion https://www.postgresql.org/message-id/CA+TgmoYGjN_f=fcerx49bzjhng+gocty+a+xhnrwcvvdy8u...@mail.gmail.com which is more important for this patch than the suggestions about encryption. > The patches at hand extend some internal file access APIs and then sprinkle > them around various places in the backend code, but there is no explanation > why or how this is better. I don't see any real structural savings one might > expect from a refactoring patch. No information has been presented how this > might help encryption. At this stage I expected feedback from the developers who have already contributed to the discussion, because I'm not sure myself if this version fits their ideas - that's why I didn't elaborate the documentation yet. I'll try to summarize my understanding in the next version, but I'd appreciate if I got some feedback for the current version first. > I also suspect that changing around the use of various file access APIs needs > to be carefully evaluated in each individual case. Various code has subtle > expectations about atomic write behavior, syncing, flushing, error recovery, > etc. I don't know if this has been considered here. I considered that, but could have messed up at some places. Right now I'm aware of one problem: pgstat.c does not expect the file access API to raise ERROR - this needs to be fixed. -- Antonin Houska Web: https://www.cybertec-postgresql.com
