On Mon, Apr 25, 2022 at 9:42 PM Michael Paquier <mich...@paquier.xyz> wrote: > On Mon, Apr 25, 2022 at 10:24:52AM -0500, David Christensen wrote: > > On Mon, Apr 25, 2022 at 6:03 AM Bharath Rupireddy > > <bharath.rupireddyforpostg...@gmail.com> wrote: > >> Thanks for working on this. I'm just thinking if we can use these FPIs > >> to repair the corrupted pages? I would like to understand more > >> detailed usages of the FPIs other than inspecting with pageinspect. > > > > My main use case was for being able to look at potential corruption, > > either in the WAL stream, on heap, or in tools associated with the WAL > > stream. I suppose you could use the page images to replace corrupted > > on-disk pages (and in fact I think I've heard of a tool or two that > > try to do that), though don't know that I consider this the primary > > purpose (and having toast tables and the list, as well as clog would > > make it potentially hard to just drop-in a page version without > > issues). Might help in extreme situations though. > > You could do a bunch of things with those images, even make things > worse if you are not careful enough.
True. :-) This does seem like a tool geared towards "expert mode", so maybe we just assume if you need it you know what you're doing? > >> 10) Along with pg_pwrite(), can we also fsync the files (of course > >> users can choose it optionally) so that the writes will be durable for > >> the OS crashes? > > > > Can add; you thinking a separate flag to disable this with default true? > > We expect data generated by tools like pg_dump, pg_receivewal > (depending on the use --synchronous) or pg_basebackup to be consistent > when we exit from the call. FWIW, flushing this data does not seem > like a strong requirement for something aimed at being used page-level > chirurgy or lookups, because the WAL segments should still be around > even if the host holding the archives is unplugged. I have added the fsync to the latest path (forthcoming), but I have no strong preferences here as to the correct/expected behavior. Best, David
