Re: MarkBufferDirtyHint() and LSN update

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.
--
Michael