On Fri, Mar 13, 2026 at 8:12 PM Tomas Vondra <[email protected]> wrote: > > On 3/5/26 21:25, Andres Freund wrote: > > Hi, > > > > On 2026-03-05 10:52:03 -0800, Noah Misch wrote: > >> On Thu, Mar 05, 2026 at 12:10:11PM -0500, Andres Freund wrote: > >>> Tomas encountered a crash with the index prefetching patchset. One of the > >>> patches included therein is a generalization of the gistGetFakeLSN() > >>> mechanism, which is then used by other indexes as well. That triggered an > >>> occasional, hard to locally reproduce, ERROR or PANIC in CI, about > >>> > >>> ERROR: xlog flush request 0/01BD2018 is not satisfied --- flushed only > >>> to 0/01BD2000 > >> > >>> To be safe, this code would need to use a version of GetXLogInsertRecPtr() > >>> that does use XLogBytePosToEndRecPtr() instead of XLogBytePosToRecPtr(). > >> > >> I agree. Thanks for diagnosing it. Feel free to move forward with that > >> strategy, or let me know if you'd like me to do it. > > > > I'd appreciate if you could do it. > > > > Here's a fix for master (and backpatching). It introduces a new function > GetXLogInsertEndRecPtr() and then uses that in gistGetFakeLSN(). I still > need to test this a bit more, but it did fix the issue in our dev branch > (where we saw regular failures). So I'm 99% sure it's fine. > > After writing the fix I had the idea to grep for GetXLogInsertRecPtr > calls that might have similar issue (being passed to XLogFlush), and > sure enough walsender does this: > > XLogFlush(GetXLogInsertRecPtr()); > > Which AFAICS has the same issue, right? Funnily enough, this is a very > new call, from 2026/03/06. Before 6eedb2a5fd88 walsender might flush not > far enough, now it may be flushing too far ;-) AFAIK it should call the > same GetXLogInsertEndRecPtr() once we have it.
Yes, this is already being discussed at [1], and Anthonin has also proposed a patch there that adds GetXLogInsertEndRecPtr(). Regards, [1] https://postgr.es/m/vzguaguldbcyfbyuq76qj7hx5qdr5kmh67gqkncyb2yhsygrdt@dfhcpteqifux -- Fujii Masao
