Antonin Houska <a...@cybertec.at> wrote: > Michael Paquier <mich...@paquier.xyz> wrote: > > > On Mon, Nov 11, 2019 at 10:03:14AM +0100, Antonin Houska wrote: > > > This looks good to me. > > > > Actually, no, this is not good. I have been studying more the patch, > > and after stressing more this code path with a cluster having > > checksums enabled and shared_buffers at 1MB, I have been able to make > > a couple of page's LSNs go backwards with pgbench -s 100. The cause > > was simply that the page got flushed with a newer LSN than what was > > returned by XLogSaveBufferForHint() before taking the buffer header > > lock, so updating only the LSN for a non-dirty page was simply > > guarding against that. > > Interesting. Now that I know about the problem, I could have reproduced it > using gdb: MarkBufferDirtyHint() was called by 2 backends concurrently in such > a way that the first backend generates the LSN, but before it manages to > assign it to the page, another backend generates another LSN and sets it. > > Can't we just apply the attached diff on the top of your patch?
I wanted to register the patch for the next CF so it's not forgotten, but see it's already there. Why have you set the status to "withdrawn"? -- Antonin Houska Web: https://www.cybertec-postgresql.com
