On Thu, Feb 1, 2018 at 7:21 PM, Simon Riggs <si...@2ndquadrant.com> wrote: > Yes, it would be about 99% of the time. > > But you have it backwards - we are not assuming that case. That is the > only case that has risk - the one where an old WAL record starts at > exactly the place the latest one stops. Otherwise the rest of the WAL > record will certainly fail the CRC check, since it will effectively > have random data in it, as you say.
OK, I get it now. Thanks for explaining. I think I understand now why you think this problem can be solved just by controlling the way we recycle segments, but I'm still not sure if that can really be made fully reliable. Michael seems concerned about what might happen after multiple recyclings, and Tom has raised the issue of old data reappearing after a crash. I do agree that it would be nice if we could make it work - saving 8 bytes per WAL record would be significant. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company
