On 2018-01-12 10:45:54 -0500, Tom Lane wrote: > Robert Haas <robertmh...@gmail.com> writes: > > On Sat, Dec 30, 2017 at 5:32 AM, Simon Riggs <si...@2ndquadrant.com> wrote: > > I have some reservations about whether this makes the mechanism less > > reliable. > > Yeah, it scares me too.
Same here. > The xl_prev field is our only way of detecting that we're looking at > old WAL data when we cross a sector boundary. Right. I wonder if it be reasonable to move that to a page's header instead of individual records? To avoid torn page issues we'd have to reduce the page size to a sector size, but I'm not sure that's that bad? > > Of course, we also have xl_crc, so I'm not sure whether there's any > > chance of real harm... > > The CRC only tells you that you have a valid WAL record, it won't clue > you in that it's old data you shouldn't replay. Yea, I don't like relying on the CRC alone at all. Greetings, Andres Freund
